CdSCdSe Quantum dots Co-sensitized TiO2 NanowireNanotube Solar Cells with Enhanced Efficience -LEIDO YA.pdf

7/24/2019 CdSCdSe Quantum dots Co-sensitized TiO2 NanowireNanotube Solar Cells with Enhanced Efficience -LEIDO YA.pdf

1/10

Electrochimica Acta 129 (2014) 379388

Contents lists available at ScienceDirect

Electrochimica Acta

journal homepage: www.elsevier .com/ locate /e lectacta

CdS/CdSe Quantum dots Co-sensitized TiO2Nanowire/Nanotube SolarCells with Enhanced Efficiency

Zhen Li, Libo Yu, Yingbo Liu, Shuqing Sun

Department of Chemistry, Tianjin University, Tianjin300072, P. R. China

a r t i c l e i n f o

Article history:

Received 19November 2013

Received in revised form 12 January 2014Accepted 24 February 2014

Available online 11March 2014

Keywords:

TiO2nanowires/nanotubes

Electrochemical oxidization

CdS

CdSe

Quantum dots sensitized solar cells

a b s t r a c t

Translucent TiO2nanowires/nanotubes (TiO2NW/NT) film would be a promising candidate in construc-

tingphotoelectrochemical solar cells for its advantages in sensitizer loading, charge separation, electronic

transport and light harvesting. In this report, translucent TiO2 NW/NT film was prepared by a two-step

anodizationmethod. The formationmechanisms ofnanowires originated fromnanotubeswere explored.

The hydrogen ions generated by electrolysis ofwater were driven by electric field to form ions flow,

which altered the interfacial stress ofnanotubes, resulting in vertically or spirally splitting the mouth of

nanotubes to form nanowires. The CdS, CdSe and CdS/CdSe quantum dots (QDs) sensitized TiO2NW/NT

solar cells were constructed. Among them, The TiO2NW/NT solar cells co-sensitized with CdS/CdSe QDs

showed higher efficiencies than ones sensitized with CdS or CdSe QDs. By varying successive ionic layer

adsorption and reaction (SILAR) cycles ofCdS/CdSe, itwas found that CdS(9)/CdSe(6)/TiO2NW/NT device

reached to a maximum power conversion efficiency of2.41%, which was 78.5% higher than that of the

CdS(9)/CdSe(6)/TiO2NT solar cell.Theexcellent photoelectrochemical properties ofour solar cell suggest

that the translucent TiO2NW/NT films co-sensitized with CdS and CdSe QDs have potential application

in photovoltaic cells.

2014 Elsevier Ltd. All rights reserved.

1. Introduction

Inexhaustible solar energy is becoming an economically viable

source of energy to provide a clean solution to the current energy

crisis. Recently, semiconductor nanocrystals (NCs), often referred

to as quantum dots (QDs), have been the focus of considerable

research attention for the development of photovoltaic cells due

to their fascinating photoelectric properties [17]. The band gap

of QDs can be tuned by controlling their size to match the solar

spectrum [8,9]. Their large intrinsic dipole moments and high

extinction coefficient can lead to rapid charge separation [10].

Moreover, theQDs provide newopportunitiestogeneratehot elec-

trons andmultipleelectron-holepairswitha singlephotonthrough

impactionization[11,12]. For these reasons,narrowbandgapsemi-

conductors QDs are ideal candidates for the optimization of solar

cell to achieve improved performance.

A typical strategy to construct quantum dots sensitized solar

cells (QDSSCs) is to use semiconductor QDs as light absorber to

sensitize wide band gap metal oxide nanostructure films such

as TiO2[1316], ZnO[17,18], and SnO2[19]. TiO2 films have been

Corresponding author. Tel.: +8613920690912.

E-mail address: [email protected] (S. Sun).

demonstrated to be a promising candidate as photoanodes due to

theirappropriateenergybandpositionandboththermalandchem-

ical stability in solution [20]. To date, TiO2NTs [2126] have been

a focus of investigation to enhance the electron transport owning

to several advantages. First, TiO2 NTs have less grain boundaries

that electrons have to pass [22], which leads to fast transport of

excited electrons. Second, highly ordered TiO2 NTs offer a vertical

path way for electron transport along the tube, which minimizes

electron loss during diffusion process [27]. What ismore, the ver-

tical tubular structure facilitates the filling of QDs sensitizer or

redox couple electrolyte [28]. In spite of these advantages, suf-

ficient QDs loading into TiO2 NTs is still a challenge in practice,

resulting in low light harvesting efficiency. Therefore, the power

conversion efficiency of QDSSCs based on TiO2 NT solar cells is

usually in lower than 1.5% [29]. Design of hierarchical structure

TiO2 film [26,28] is a good approach to overcome the disadvan-

tages of poorsensitizers loading,thereforetranslucent hierarchical

TiO2NW/NTfilmwas designedbyus. Two important issues can be

resolved with application of this translucent TiO2 NW/NT film in

QDSSCs. First,the TiO2nanowires entangledwitheach other on top

ofnanotubesallows the diffusionof QDs sensitizers throughmulti-

plepathwaysto enhance QDs loading andlightharvesting. Second,

theTiO2NW/NTpossessesa largersurfaceexposurearea to theliq-

uid redox couple electrolyte, which increases area of solid-liquid

http://dx.doi.org/10.1016/j.electacta.2014.02.145

0013-4686/ 2014 Elsevier Ltd. All rightsreserved.
http://localhost/var/www/apps/conversion/tmp/scratch_2/dx.doi.org/10.1016/j.electacta.2014.02.145http://www.sciencedirect.com/science/journal/00134686http://www.elsevier.com/locate/electactamailto:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_2/dx.doi.org/10.1016/j.electacta.2014.02.145http://localhost/var/www/apps/conversion/tmp/scratch_2/dx.doi.org/10.1016/j.electacta.2014.02.145mailto:[email protected]://crossmark.crossref.org/dialog/?doi=10.1016/j.electacta.2014.02.145&domain=pdfhttp://www.elsevier.com/locate/electactahttp://www.sciencedirect.com/science/journal/00134686http://localhost/var/www/apps/conversion/tmp/scratch_2/dx.doi.org/10.1016/j.electacta.2014.02.145


2/10

380 Z. Li et al. / Electrochimica Acta 129 (2014) 379388

junction. This can promote the charge separation of the photo-

generated electrons and holes so as to enhance photocurrent. To

our best knowledge, this translucent TiO2 NW/NT film applied to

QDSSCs is rarely reported.

In this report, translucent TiO2 NW/NT films were successfully

fabricated by a two-step anodization approach, and the formation

mechanism of the TiO2 NW/NT was explored as well. The TiO2NW/NT film co-sensitized with CdS/CdSe QDs was used as front

side illuminated photoanode in solar cells. By optimizing the SILAR

cycles of CdS/CdSe QDs, theCdS(9)/CdSe(6)/TiO2NW/NTfilmsolar

cell reached to a maximum power conversion efficiency of 2.41%,

which is significantly higher than that of the CdS(9)/CdSe(6)/TiO2NT filmsolar cell (1.35%). Our CdS/CdSe QDs co-sensitized translu-

cent TiO2NW/NT film solar cells open up a newway for designing

highefficiencyQDSSCs.

2. Experimental

2.1. Materials

The following chemical agentswere used: titanium foils (99.6%

purity, Tianjin, China), ammonium fluoride (NH4F, AR), ethylene

glycol (HOCH2CH2OH, AR), hydrogen peroxide (30wt % H2O2),deionized water (H2O, 18.2Mcm resistivity), cadmium nitrate

(Cd(NO3)24H2O, AR), sodium sulfide (Na2S9H2O, AR), sodium

sulfite (Na2SO3, AR), selenium powder (Se, AR), sulfur powder (S,

AR). All thesematerials were used directly in experimentswithout

further purification.

2.2. Fabrication of translucent TiO2NW/NT film

The TiO2NW/NT filmwas prepared bya two-step electrochem-

ical anodization method. Ti foil with the dimension of 20 mm

10mm0.1mmwasdegreasedby sonicating inacetone,deionized

water and ethanol for 10min respectively, andfinally dried in air.

In the first electrochemical anodizationprocess, the cleaned Ti foil

was anodized in Teflon electrolysis cell with a two-electrode con-figuration, whichTi foil worked asworking electrode andgraphite

sheet (15mm25mm)workedas counter electrode. Thedistance

between the two electrodes was 50mm. The electrolyte consisted

of ethylene glycol, NH4F (0.5wt %) and deionized water (3vol %).

After anodization, the anodized Ti foil was ultrasonically washed

in ethanol for 5min to remove the debris on the surface of sam-

ple, and then dried in air. In order to form anatase TiO2phase, the

anodizedTi foilwascalcined inmuffle furnaceat450Cfor1hwith

heating rateof5 C/min,and thenwascooled to room temperature

with cooling rate of 2 C/min.

After sintering treatment, the first anodized product was

anodized again in the same stock electrolyte at constant poten-

tial of 10V for 3h. Then the second anodized Ti foil was rinsed in

ethanol anddried in air. Subsequently, the product was immersedinto 10wt % H2O2 aqueous solution for 12h. Following this, the

free-standing translucent TiO2 membrane would be separated

automatically or detached by tweezers from the Ti substrate.

2.3. Construction of CdS/CdSe QDs co-sensitized TiO2NW/NT film

on FTOElectrodes

Thefollowingprocedureswereundertaken inorderto construct

photoanode electrodes. First, 2mmol of butyl titanate was added

into the 10mLof anhydrous ethanol under slowly stirring to form

a viscous solution. After a few minutes stirring, two drops of the

solutionwere dropped on theFTOglass (20mm20mm) as adhe-

sive. Then translucent TiO2NW/NT film was covered on the top of

the adhesive and dried in air for a fewminutes. After that, the TiO2

NW/NT film on FTO glass was annealed at 450 C for 30min. The

size of the TiO2NW/NT film was 0.25 cm2 (5mm5mm).

The TiO2 NW/NT films electrodes were sensitized in situ with

CdS and CdSe by SILAR. The electrodes were immersed in 0.1M

Cd(NO3)2 aqueous solution for 3min and rinsed with deionized

water and ethanol for 30s respectively; then dipped for an addi-

tional 3min in 0.1M Na2S aqueous solution and rinsedwith water

andethanol respectively for 30s. All of these processes constituted

one SILAR cycle. The deposition of CdSe was also conducted by

SILARwithalternately immersingelectrodes in0.1MCd(NO3)2and

0.1M NaSeSO3 aqueous solution for 5min, respectively. NaSeSO3solution was prepared by refluxing Se powder and NaSO3at 96

C

[30]. Different SILAR cycles of CdS and CdSe were conducted to

investigate the optimal combination cyclesof the twokinds ofQDs

for the best performance of solar cells. In addition, TiO2 NT filmof

the same thickness to TiO2 NW/NT was also prepared to explore

if the TiO2 NW/NT electrode has significant effect on the power

conversion efficiency of QDSSCs.

2.4. Fabrication of counter electrodes and cell assembly

Cu1.8S/CuS counter electrodes were prepared viahydrothermal

method reported by Kalanur et al. [31]. In brief, FTO glasses

predrilled with two holes for injection of electrolyte were cleanedby sonication in acetone, deionized water and ethanol for 10min

respectively. Then 25mL of 0.1M copper sulfate and 0.05M

thiourea aqueous solution were mixed together. The mixed solu-

tion was quickly transferred to the autoclave, filling 80% volume.

TheFTO substratewasplacedat anangleagainst thewall of Teflon-

liner with the conducting side facing down. The hydrothermal

reactionwas conducted at 150 C for 2h.

The QDs sensitized TiO2 NW/NT electrodes and Cu1.8S/CuS

counter electrodeswere assembled in a sandwich fashion cell. The

Surlyn film with thickness of 60mwas used as spacer. The solu-

tion of0.5M sodiumsulfide and0.1M sulfurdissolvedin deionized

water as liquid electrolyte was injected into the space of solar cell

through one hole on the counter electrode.

2.5. Characterization

Scanning electron microscopy (SEM) images were recorded

using a Hitachi S-4200 field emission SEM equipped with an

energy dispersive X-Ray (EDX) spectrometer. Transmission elec-

tron microscope (TEM) images of samples were obtained by a

Tecnai G2 F20 at 200kV. The crystalline nature and structure of

TiO2NW/NTfilmwere analyzedby X-Raydiffraction(XRD,D/MAX-

2400, Rigaku) using a Cu K source operated at 40kV and 30mA

with scanningrateof 2/min. Theopticalabsorbanceof thesamples

was recorded using a UV2501PC (SHIMADZU) spectrometer with

an ISR-2200 integrating sphere attachment for diffuse reflection

measurement. Thecurrent-voltagecharacteristicswereperformed

with Oriel I-V test station by Newport. A solar simulator (Pecell-L15, Japan)whichcalibrated by standard silicon solar cell (BS-520,

Japan) was used to simulate sunlight with irradiation intensity of

100mW/cm2. The incidentphoto-to-current conversion efficiency

(IPCE)wasmeasured as a function of wavelength from 300nm to

800nmby using a model 7-SCSspec II system.

3. Results and discussion

3.1. The Formation of Translucent TiO2NW/NT Film

The top morphology of TiO2 NT, TiO2 NW/NT and their cor-

responding cross-section images were obtained from FE-SEM. As

shown in Fig. 1a, highly ordered TiO2 NT arrays were formed on

Ti substrate after the first electrochemical anodization at 50V for


3/10

Z. Li et al. / Electrochimica Acta 129 (2014) 379388 381

Fig. 1. Top morphology of (a) TiO2 NT and (b) TiO2 NW/NT. Inset of (b) is optical image of NW/NT film. (c) SEM image of NWs on top of NTs. (d) Cross-section images of

TiO2NT and (e) TiO2 NW/NT. (f)Back side morphology of TiO2 NW/NT. (g) TEM of TiO2 NT. (h) SAEDof TiO2NT without annealing treatmentand (i) TiO2NT with annealing

treatment.

6h. The diameter of the NT is around 110nm and the wall thick-

ness is about 15nm. Fig. 1b gives the top view of translucent TiO2NW/NT film. It shows NWs appeared on the surface of the TiO2

NT arrays after the second anodization at 10V for 3h and thetubular structure beneath the wires still remain ordered, which

indicates this two-step electrochemical anodization approach is

feasible for the synthesis of hierarchical TiO2 NW/NT nanostruc-

ture.Thewhole TiO2NW/NTmembranewith faint yellowcolor and

translucence remained integrity after being peeled off from the Ti

substrate (inset ofFig. 1b), providing its application value as front

illuminated photoanode in QDSSCs. The NWs are about 11.5m

in length and 2030nm in diameter as shown in large magnifica-

tion SEM ofFig. 1c. Although the nanowires originated from the

second anodization, the thickness of NW/NT film is almost unvar-

iedcomparingwith the TiO2NT filmprepared byfirst anodization.

Both Fig. 1d and 1epresent that the thicknesses of the TiO2NTfilm

and TiO2 NW/NT film are about 6m, indicating that the second

anodizationprocessonlycontributedto theformationofnanowiresontop ofTiO2NT arraysand hasno obvious effecton the longitudi-

nal growth of nanotube. Thebackside view of the translucent TiO2NW/NT film in Fig. 1fshows that the nanotubes possessed sealed

ends, and the integrity of the TiO2 NT arrays was preserved well

after the separation from titaniumsubstrate. Fig. 1g is The TEM of

the TiO2NT, showing that thefirst anodizedsamplehas anordered

tubularstructure.The selectedareaelectrondiffraction(SAED)pat-

terns fromtheTEMofTiO2NT before andafterannealing treatment

at 450 C were given in Fig. 1h and Fig. 1i, respectively. Before

the heat treatment, no electronic diffraction rings can be seen in

Fig. 1h, which indicates that the TiO2 NT produced by anodiza-

tion was amorphous. The TiO2 NT transformed from amorphous

to crystalline after the annealing treatment, whichwas proved by

the appearance of electronic diffraction rings in SAED ofFig. 1i.

X-ray diffraction (XRD) patterns were used to further charac-

terize the phase structure transformation of TiO2from amorphous

to crystalline. As shown in Fig. 2a, only diffraction peaks of tita-

nium can be indexed (JCPDS file 44-1294) in the first anodizedTi foil, which means the as-prepared TiO2 NT on Ti substrate

was probably amorphous. This result was in accordance with

the SAED from TEM of un-annealed TiO2 NT. After annealing at

450 C for 1h, the TiO2 transformed from amorphous to anatase

phase. In XRD pattern of anatase TiO2 NT, both diffraction peaks

of Ti and anatase TiO2 (JCPDS file 21-1272) can be indexed. The

typical sharp peak at 25.3 corresponding to the (101) plane

of anatase TiO2 confirms the crystalline phase transformation

from amorphous to anatase at 450 C. For the translucent TiO2NW/NT film, the peaks belonging to Ti have been disappeared,

and all of diffraction peaks can be attributed to the anatase TiO2phase.

The elementary composition analysis of the free-standing TiO2

NT and TiO2 NW/NT films were carried out by energy dispersiveX-Ray (EDX) spectrometer. The peaks corresponding to carbon,

oxygenandtitaniumappeared in thespectra ofFig. 2b and 2c.Eth-

ylene glycol wasabsorbed into TiO2NTs during the process of first

anodizationandwasburnedtoCO2 andH2Oinfurnaceatmosphere.

However, it is possible that not all the ethylene glycol was con-

sumedtoproduceCO2, somemaybe transforminto carbon residing

in TiO2NTs due to the insufficient of oxygen in the furnace, which

resulted in the presence of carbon in EDX spectra. The dominant

elements in the two EDX spectra are titanium and oxygen, imply-

ingthatthefilmsweremainlycomposedofTi andO.However,both

of the two EDX spectra showed that the ratio between Ti and O is

muchmore than 1:2. It seems that there was more Ti than O. The

possible reasonmaybe that amorphousTiwas introduced into the

TiO2 NT and TiO2 NW/NT during the first and second anodization


4/10


Fig. 2. (a) XRD patterns for amorphous TiO2 NT on Ti, anatase TiO2 NT onTi, and

translucent TiO2 NW/NT film, respectively. (b) EDX spectrum of TiO2 NT film. (c)

EDXspectrumof TiO2NW/NT film.

since the XRD did not show any crystalline Ti in the TiO2 NW/NT

film.

The growth of TiO2 NT on Ti substrate was determined by two

main reactions as follows:

Ti + 2H2O TiO2+4H++4e- (1)

TiO2+4H++6F- [TiF6]

2-+2H2O (2)

Thereaction(1) is theprocessofelectrochemicaloxidation(EO),

leading to the formation of amorphous TiO2 barrier layer on the

surface of Ti substrate, and the reaction (2) is called the chemical

etching (CE) processwhichresults in theformationofpits onamor-

phous TiO2surface.Onlywhen thereactionrate of EO is fasterthan

the reaction rate of CE, the TiO2 NTs can be produced according

to previous report [32]. At first, the amorphous TiO2 barrier layer

was formed by EO; meanwhile the F- in electrolyte began to etch

the surface of barrier layer to produce pits, which is called pitting

attack process. Then the pits were developed into tubular struc-

tureby prolonginganodizationtime.A thinamorphousTiO2 barrier

layer would exist between nanotubes layer and Ti substrate due

to the rate of EO superiors to the rate of CE; and after annealing

at 450 C for 1h, the amorphous TiO2 was transformed to anatase

TiO2as shown in first anodization part ofFig. 3.

The formation process of the translucent TiO2 NW/NT film is

summarized in second anodization part ofFig. 3. During the sec-

ond anodization, a lower potential of 10V was applied to the first

anodized samplein thesame stock electrolyte. TheTiO2NWswere

generated from the top of the TiO2 nanotubular arrays in this

step;meanwhile, a newamorphous TiO2barrier layer was formed

again beneath the anatase TiO2 NT arrays. After rinsed in ethanol

and dried in air, the second anodized sample was immersed in

10wt% H2O2 aqueous solution for 3h to dissolve the new formed

amorphous TiO2 layer, and then the TiO2 NW/NT membrane was

separated from theTi substrate.

The possible models for the origination of nanowires from

TiO2 NT arrays are proposed in Fig. 4. We hypothesized that the

nanowires originated from the split of the TiO2 nanotubes.Water

playedan important rolein secondary anodizationwiththe appliedpotentialof 10V. Inthisstage,waterwas electrolyzedat thebottom

of the TiO2tubular anode. Twomain reactions probably happened

as follows:

H2O H++OH

-(3)

2OH- H2O + O

2 (4)

The O2 generated from electrolysis as source of oxygen con-

tributed to the new amorphous TiO2 layer which would be

dissolved by H2O2 to produce free-standing TiO2 NWNT film in

post-treatment, while H+ would help to generate the wires at the

mouth of nanotubes. According to the reported literature [33],

H+ was limited at the bottom of nanotubes under high potential

(>20V), forming a localized acidification atmosphere which wasfavorable to chemical etching for prolonging nanotubes. However,

the voltage of 10V in our second anodization process was nothigh

enough to confine the H+ at the bottomof the tubes in the viscous

ethylene glycolsolution, therefore, the H+ generatedat thebottom

of nanotube would be driven to the cathode by electric field, this

may lead to H+ flow through the bottom to the mouth of nano-

tubes. However, the movingway of H+ flowin nanotubemayhave

two different forms: vertical motion or spiral motion in the nano-

tubes.Atthe tubemouth,theH+ flowcreates an interfacialstressof

nanotubes in theviscous electrolyte.With the assistance of chem-

ical dissolution along this stress on TiO2 nanotubes electrode, the

mouth of nanotubes split vertically or spirally to form nanowires

as depicted in Fig. 4. In addition,waterelectrolysis in ethylene gly-

col mediumwas an inefficient reaction [34], the chemical etchingprocesswas suppressed and the splittingreactionwas also limited

to the mouth of the nanotubes, which led to the nanowires orig-

inated only on the surface of TiO2 nanotubular arrays. The path 1

is similar to the mechanism bamboo-splitting model previously

reported by J. H. Lim [33], and we infer that if the vertical split of

nanotube is the dominant reason for the formation of TiO2 NWs,

the length of the nanotubewould be shorted. However, in contrast

with cross-section image ofFig. 1d and 1e, it can be distinguished

that thelengthsof tubesforTiO2NW/NTandTiO2NTarealmost the

same. Therefore, we proposed the spiral split mechanism (path 2)

to interpret this phenomenon.The diameter of theTiO2NT isabout

110nmwhen prepared at 50V for 6h; hence the circumference of

the tube is about 345nm, which means that only three to four cir-

cles of spiral split are enough for the nanowires length of around


5/10


Fig. 3. The formationprocess of free-standing translucent TiO2 NW/NTmembrane by a two-step anodization approach.

11.5m. No obvious variation of the tubes length between TiO2NW/NTandNTfilmconfirmed therationality of the spiral splitting

mechanism. We believe that both the vertical and spiral splitting

paths contributed to the origination of nanowires from TiO2 NT

arrays in secondary anodization process, and the spiral splitting

may havemore contribution.

3.2. Photoanodes Analysis

QDs sensitized photoanodes were fabricated by variation of

SILAR cycles in Cd, S and Se precursor solution respectively. The

whole surface of TiO2 NW/NT film and CdS(9)/CdSe(6) QDs sensi-

tized TiO2NW/NT film are presented in Fig. 5a and5b respectively.

The surface of CdS(9)/CdSe(6) NW/NT film (Fig. 5b) was obviouslyrougher than that of TiO2 NW/NT film, indicating the successful

deposition of CdS/CdSe QDs on TiO2NW/NT film. Especially in the

area with NWs in Fig. 5b, the surface of the filmwas almost cov-

ered by quantum dots, which suggested that the NWs on top of

NTs boost the adsorption of CdS/CdSe QDs. In addition, TiO2 NTs

beneath wires also adsorbed QDs, which were confirmed by the

decreaseof inner tube diameter asshownin the insetofFig.5b. The

image of TiO2NWs that adsorbedQDs was given by SEM inFig. 5c,

it can be seen that the large amountofQDs werefilled in the inter-

spacesamong the nanowires after theSILAR,and TEMimage (inset

ofFig. 5c) clearly showedthat the distributionof QDs onTiO2NWs.

Fig. 5d is the TEM of the tubular part of the sensitized TiO2NW/NT

film, showing that QDs can also be found inside the nanotubes.

The distribution of QDs in nanowires and nanotubes manifested

that this TiO2 NW/NT hierarchical structure can enlarge the QDs

loading.

The photographs of CdS(15)/TiO2 NW/NT, CdSe(15)/TiO2

NW/NT and CdS(9)/CdSe(6)/TiO2 NW/NT electrodes are shown inFig. 6a, 6c and 6e respectively. Visibly, these samples showed sin-

gle and unique colorswith good uniformity across the surface and

the color changed from yellow to red as the introduction of CdSe

QDs to the NW/NT film. In order to further confirm the successful

Fig. 4. Originationmechanismof nanowires fromTiO2nanotube by secondaryanodization.


6/10


Fig. 5. SEM images of (a) TiO2 NW/NT film and (b) CdS(9)/CdSe(6)/TiO2 NW/NT film, inset is large magnification SEM from tubes area. (c) Large magnification SEM from

wires area, inset is the TEM ofNWs sensitizedwithQDs.(d) TEM ofthe TiO2NTs sensitized with QDs.

depositionofCdS/CdSeQDson TiO2NW/NTfilm,threetypesofpho-

toanodeswereanalyzedbyEDXspectra. Fig.6b, 6dand6fshowthe

EDXspectraof theCdS(15)/TiO2NW/NT,CdSe(15)/TiO2NW/NTand

CdS(9)/CdSe(6)/TiO2NW/NT electrodes. Thecharacteristic peaksof

Cd and S elements are presented in Fig. 6b, indicating that the CdS

QDs have been successfully assembled on the TiO2 NW/NT film.Apparently, atom content of Cd and Se in EDX spectrum ofFig. 6d

is extremely low, which means that only a few CdSe QDs can be

depositedonTiO2NW/NTfilmwith15SILARcycles. However, first

deposition of CdS on TiO2 is favorable for further sensitization of

CdSe QDs, which is verified by EDX spectrum ofFig. 6f. As we can

see, the atom content of Se is greatly enhanced, and the atomic

ratio of S and Se to Cd nearly equal to 1:1 (3.09 At% of Se, 4.24

At% of S and 6.21 At% of Cd). This chemical analysis provides the

evidence of the formation of CdS/CdSe QDs on TiO2 NW/NT film

photoanode. Theeffectivedeposition of thequantumdots can also

be identified by naked eyes, as there is no observable coloration

inhomogeneous across the surface of CdS(9)/CdSe(6)/TiO2NW/NT

electrode in Fig. 6e.

3.3. UV-Visible Diffuse-Reflectance

The UV-vis diffuse reflectance absorbance spectra of our sam-

ples areillustratedin Fig.7. TheTiO2NW/NTfilm(Fig.7a) showeda

mainabsorption edgeat380nm, correspondingto 3.26eV, which

was in accordance with thebandgap of anatase TiO2. However, the

UV-vis spectrumof CdS(9)/TiO2NW/NT film (Fig. 7b) exhibitedred

shift of broad absorption edge to 530nm. This result indicated that

the deposition of CdS QDs on TiO2 NW/NT film enlarged the light

absorption range tovisible region.While in the UV-vis spectrumof

CdS(9)/CdSe(6)/TiO2film (Fig. 7c), a further red shift of adsorption

edge to 700nm implied that successful deposition of CdSe QDs on

CdS/TiO2 NW/NT. This variation demonstrated that the deposition

of CdS/CdSe QDs has significantly extended the photoresponse of

TiO2NW/NT electrodefromultraviolet light tonearly entire visible

light region. The outcome can be interpreted as follows: the CdS

QDs onTiO2 NW/NTmay act as a seed layer to facilitate the nuclea-

tion of CdSe QDs due to the small lattice mismatch between CdS

and CdSe [14]. Therefore, it is anticipated that the CdS/CdSe/TiO2NW/NT film structure is a promising candidate in photovoltaic

devices.

3.4. J-V Performances of the QDSSCs

Various CdS/CdSe co-sensitized TiO2/NW/NT solar cells were

assembled and their photovoltaic performanceswere investigated

by Oriel I-V test station under 1 sun (= 100 mW/cm2 AM1.5G

solar illumination). Fig. 8a compares the current density-voltage

characteristics of three solar cells assembled with CdS(15)/TiO2NW/NT, CdSe(15)/TiO2 NW/NT and CdS(9)/CdSe(6)/TiO2 NW/NT

electrodes. The CdS(15)/TiO2 NW/NT exhibited short circuit cur-

rent (Jsc), open voltage (Voc) and power conversion efficiencyvalues () of 4.78mA/cm2, 0.34V and 0.59%, respectively. While

the CdSe(15)/TiO2 NW/NT showed much lower Jsc (1.94mA/cm2)

due to low coverage of CdSe on TiO2 NW/NT. It is worth noting

that the photovoltaic performance of CdS(9)/CdSe(6)/TiO2 NW/NT

photovoltaic device was significantly improved, possessingJsc, Vocand of 14.73mA/cm2, 0.47V and 2.41%, respectively. Two main

reasons are probably responsible for the improvement. First, CdS

QDs layerswere favorableformore adsorption of CdSe QDs, result-

ing in a complementary effect [16] in light harvesting due to the

expansion of the scope of light absorption (as shown in Fig. 7b and

7c), which benefits for the increase ofJsc. In addition, TiO2NW/NT

filmco-sensitizedwith CdSandCdSe increased the Vocby forming

cascading band structure, which can effectively separate excitons

at the junctions [18].


7/10


Fig. 6. Opticalimagesand EDX spectra ofCdS (a, b), CdSe (c, d), and CdS/CdSe(e, f)sensitized TiO2 NW/NTphotoanode.

Fig.7. Diffuse-reflectanceUV-visible spectraof(a) TiO2NW/NTfilm, (b)CdS(9)/TiO2

NW/NTphotoanode, (c) CdS(9)/CdSe(6)/TiO2 NW/NTphotoanode.

To further investigate the optimal combination of CdS and

CdSe, CdS/CdSe/TiO2NW/NT solar cells with differentSILAR cycles

were fabricated. Fig. 8b depicts the J-Vperformance variation of

these solar cells, and Fig. 8c gives the power conversion effi-

ciency as the function of different SILAR cycles of CdS/CdSe. The

CdS(9)/CdSe(6)/TiO2 NW/NT solar cell yielded the highest of

2.41% with the Jsc, Voc and fill factor (FF) values of 14.73mA/cm2,

0.47V and 0.35 respectively. The performance parameters of vari-oussolar cells aresummarized in Table 1. As it shows, the valuesof

Jsc,Vocand of single CdSor CdSeQDs sensitized TiO2NW/NTsolar

cells are lower than any of CdS/CdSe/TiO2NW/NT solar cells. The

values of co-sensitized solar cells were influenced by the different

SILAR cycles of CdS and CdSe QDs. Appropriate cycles of CdS were

not only beneficial for the absorption of light but also in favor of

the deposition of CdSe, which is helpful for the improvement of.

As illustrated inFig.8c, TheCdS(3)/CdSe(12)/TiO2NW/NTsolar cell

hasa lowervalue (0.77%). The reachedtothemaximumvalueof

2.41%when the SILAR cycles of CdS and CdSewere9 and 6, respec-

tively. However, further increaseSILARcyclesof CdSresulted inthe

reduction of, whichwas presented by the CdS(11)/CdSe(4)/TiO2NW/NT solar cell with of 1.08%. Anexcessive amount of CdS QDs

on TiO2 NW/NT probably provided more recombination sites or


8/10


Fig. 8. IlluminatedJ-Vcharacteristics of (a) TiO2 NW/NT sensitized by CdS(15), CdSe(15) and CdS(9)/CdSe(6). (b) TiO2 NW/NT filmsolar cells with different SILAR cycles of

CdS andCdSe. (c) The power conversion efficiency as the function of different CdS/CdSe SILAR cycles. (d)J-Vcurves of CdS(9)/CdSe(6) devices employing TiO2 NW/NT and

TiO2NT.

led to local block in nanotubes, whichhindered the efficient trans-

port ofphotogeneratedelectrons fromQDs tothe TiO2photoanode,

causing the decrease of the power conversion efficiency.

In order to interpret that the performance of TiO2NW/NT solar

cell is better than TiO2 NT solar cell, the translucent TiO2 NT film

was prepared according to the method proposed by Chen et al.

[35] as comparison group. TheTiO2NT filmpossessed the identical

diameter and thickness to TiO2 NW/NT was obtained by control-

ling reaction conditions to insure only the structure is the factor

that influence the performance of solar cells. Fig. 8d illustrates the

J-Vcharacteristics of TiO2NW/NT and TiO2NT film solar cells sen-

sitized with CdS(9)/CdSe(6) QDs. Both of the solar cells presented

almost sameVocand FF. However, theJscof TiO2NW/NT solar cell

is markedly enhanced in contrast with that of TiO2 NT solar cell.

The increment ofJsc resulted in the enhancement of from 1.35%

to 2.41%.

The incident photo-to-current conversion efficiency (IPCE) of

TiO2NW/NTandTiO2NT solarcellssensitizedwith CdS(9)/CdSe(6)

QDs are shown inFig.9. In general, the IPCE spectra of the twosolar

cells were consistent with the corresponding UV-vis spectrum of

CdS(9)/CdSe(6)/TiO2NW/NTphotoanode (Fig. 7c), which indicated

that most of the visible region light was absorbed by CdS/CdSe

quantum dots and involved in the photocurrent generation. IPCE

values as high as 48.6% can be achieved by the TiO2 NW/NT solar

Table 1

I-Vcurve parameters measured at 1 sun illumination.

Sample Jsc(mA/cm2) Voc (V) FF Efficiency (%)

CdS(15)/TiO2NW/NT 4.78 0.34 0.36 0.59

CdSe(15)/TiO2 NW/NT 1.94 0.34 0.38 0.25

CdS(3)/CdSe(12)/TiO2NW/NT 6.65 0.38 0.30 0.77

CdS(5)/CdSe(10)/TiO2 NW/NT 8.54 0.44 0.33 1.22

CdS(7)/CdSe(8)/TiO2 NW/NT 12.17 0.38 0.39 1.80

CdS(9)/CdSe(6)/TiO2 NW/NT 14.73 0.47 0.35 2.41

CdS(11)/CdSe(4)/TiO2NW/NT 7.96 0.42 0.32 1.08

CdS(9)/CdSe(6)/TiO2 NT 9.02 0.47 0.32 1.35


9/10


Fig. 9. IPCE spectra of theCdS(9)/CdSe(6) based on TiO2 NW/NT and TiO2 NT solar

cells.

cell, but the values obtained by the TiO2 NT device are only about

38.7%. This result indicates that theTiO2NW/NTstructure not only

maintains the advantage of the nanotube such as efficient charge

separation and swift electron transport properties, and even per-forms better than TiO2 NT. The relatively excellent IPCE value of

the CdS/CdSe/TiO2 NW/NT solar cell manifested its great promise

for the construction of high performance quantum dots sensitized

solar cells.

The configurations of our co-sensitized solar cells are depicted

inFig. 10a and10b.Basedon theseschemes,Wehereproposedsev-

eralpossible reasons to interpret theenhancementof performance

for TiO2 NW/NT solar cell: first, the TiO2 NW/NT structure retains

the advantage of the nanotube such as efficient charge separation

and swift electron transport properties, which was confirmed by

IPCE spectra; second, the appearance of nanowires on topof tubes

have significantly enlarged theadsorption of quantum dots, which

was evidenced by SEM and TEM images fromFig. 5; third, thefine

heterojunction formedbetween CdS and TiO2NW/NT is beneficialfor CdS QDs to collect excited electrons fromCdSe QDs to the con-

ductionbandofTiO2 inthe stepwisebandedgealignment asshown

in Fig. 10d; finally, TiO2 NW/NT structure increases the deposi-

tion areas of CdSe, which probably leads to the local existence of

Fig.11. Photocurrentstability of CdS(9)/CdSe(6)/TiO2NW/NTcell undercontinuous

illumination of 100mW/cm2.

CdSe/TiO2 interface that will aggrandize the effect cover area and

consequently improve the photocurrent [36].

The photostability of QDSSC is another very important issue.

Thus the stability of CdS(9)/CdSe(6)/TiO2 NW/NT solar cell wasinvestigatedbyrecordingJscvariationunder thecontinuous illumi-

nation(Fig. 11). Duringthe first 60min of irradiation,a stableshort

circuit current density of 14.714.5mA/cm2 was observed, which

demonstratedanexcellentstability of thesolar cellduringthemea-

surement. The photostability could be attributed to efficient holes

scavenging capability of polysulfide electrolyte, which successfully

suppresses hole-induced anodic corrosionof theCdS/CdSe QDs.

Despite theCdS(9)/CdSe(6)/TiO2NW/NT solar cell hasachieved

an acceptable conversion efficiency of 2.41%, it can be anticipated

that there is stillmuch space for further improvementof thepower

conversion efficiency, in particular by augmentation ofVocand FF.

For instance, a ZnS capping layer[9] and annealing treatmentmay

reduce the undesired surface trapping, or new counter electrode

materials[37,38] being applied to facilitate the catalytic reduction

of the redox electrolyte. This will be the focus of our continuing

research work. In this research, our CdS/CdSe/TiO2 NW/NT solar

cell opens up new avenue for further development of high power

conversion efficiency QDSSCs.

Fig.10. Configurationof CdS/CdSe co-sensitized solar cells based on (a)TiO2 NW/NT and(b) TiO2NT, respectively. (c) Band-edgepositionsof TiO2, CdS,and CdSe inbulk. (d)

Proposed realignment band-edges for CdS/CdSe/TiO2electrode in equilibriumwith the redoxcouples electrolyte.


10/10
http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0190http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0185http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0180http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0175http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0170http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0165http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0160http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0155http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0150http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0145http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0140http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0135http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0130http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0125http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0120http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0115http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0110http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0105http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0100http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0095http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0090http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0085http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0080http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0075http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0070http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0065http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0060http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0055http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-4686(14)00476-9/sbref0050http://refhub.elsevier.com/S0013-

Documents

CdSCdSe Quantum dots Co-sensitized TiO2 NanowireNanotube Solar Cells with Enhanced Efficience -LEIDO YA.pdf