Flexible organic-inorganic hybrid photodetectors with n ... · Flexible organic-inorganic hybrid photodetectors with ... integrates electronic/optoelectronic devices on flexible substrates,

Nano Res

1

Flexible organic-inorganic hybrid photodetectors with

n-type PCBM and p-type pearl-like GaP nanowires

Gui Chen,† Xuming Xie,

† and Guozhen Shen ()

Nano Res., Just Accepted Manuscript • DOI: 10.1007/s12274-014-0537-5

http://www.thenanoresearch.com on July 7, 2014

© Tsinghua University Press 2014

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Nano Research

DOI 10.1007/s12274-014-0537-5



Gui Chen, Xuming Xie, and Guozhen Shen*

Institute of Semiconductors, Chinese Academy of

Sciences, China

Flexible organic-inorganic hybrid photodetectors were

fabricated on various flexible substrates for the first time with

n-type PCBM and p-type pearl-like GaP nanowires, which

exhibited high mechanical flexibility, good folding strength,

excellent electrical stability and fast response.

Guozhen Shen, http://nanolab.tap.cn

http://nanolab.tap.cn/



Gui Chen,† Xuming Xie,† and Guozhen Shen ()

† G. Chen and X. Xie are visiting students from Huazhong University of Science and Technology. They contribute equally to this

work.

Received: day month year

Revised: day month year

Accepted: day month year

(automatically inserted by

the publisher)

© Tsinghua University Press

and Springer-Verlag Berlin

Heidelberg 2014

KEYWORDS

Nanowires; flexible;

photodetectors; hybrid

ABSTRACT

Flexible photodetectors have become one of the focuses of current researches

becaused of they may fit for some unique applications in various new areas that

require flexible, lightweight, and mechanical shock-resistive sensing elements.

In this work, we designed flexible organic-inorganic hybrid photodetectors on

various flexible substrates, including PET, common sellotape and PDMS, with

n-type PCBM and p-type pearl-like GaP nanowires (NWs) as the active

materials. The as-fabricated hybrid devices exhibited optimized performance

with a fast response time (43 ms) and high on/off ratio (~170) compared with

the device made of pristine GaP NWs. Under different bending condition, the

flexible hybrid photodetectors demonstrated excellent flexibility and electrical

stability, which are very promising for further large-scale, high sensitivity and

high speed photodetector applications.

1 Introduction

Photoresponse is a general property of

semiconductors and photodetection is of great

importance for various applications including

environmental and biological research, sensing,

detection and missile launch. Many kinds of

photodetectors with response to either deep UV light,

visible light, infrared light or broad wavelength

lights have been designed and demonstrated [1-5].

Recently, the use of hybrid nanostructures in

photodetectors has been an emerging research topic

due to their high surface-to-volume ratio, as well as

more freedom in the rational design of material

properties [6-9]. Heterostructures formed between

inorganic and organic materials could lead to many

unique device applications due to their unique

physical properties, such as mechanical flexibility,

large area, low temperature processability and high

performance. These hybrid materials demonstrated

not only the merits of organic polymer and inorganic

semiconductor, but also the advantage of the

interfaces between the components for the

transmission of electrons and holes [6-9]. Among the

investigated hybrid nanostructures, one-dimensional

(1-D) organic-inorganic hybrid nanostructures have

been widely investigated very recently as they

usually demonstrated excellent photovoltaic

behavior, rectification, light-emitting behavior and

photoresponse properties [10-14]. Photodetectors

built on these hybrid materials usually exhibited

superb photoresponse to light irradiation.

Nano Research

DOI (automatically inserted by the publisher)

Address correspondence to [email protected].

Research Article

mailto:[email protected]

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2 Nano Res.

Flexible electronics, referring to the technology that

integrates electronic/optoelectronic devices on

flexible substrates, have gained extensive attention

because of the attractive properties of flexible devices

such as biocompatibility, flexibility, light weight,

shock resistance, softness and transparency, as well

as the potential applications in future wearable

devices, paper displays, sensors and detectors,

energy conversion and storage devices.

In this work, by utilizing n-type

phenyl-C61-butyric acid methyl ester (PCBM) and

p-type GaP NWs as the sensing materials, we

designed high-performance flexible hybrid

photodetectors on various flexible substrates.

Pearl-like GaP NWs were first grown via a simple

chemical vapor deposition (CVD) method and their

electric transport and photoresponse properties were

investigated by fabricating single NW devices. By dip

coating mixed GaP:PCBM solution on flexible

substrates, including PET, common sellotape and

PDMS, highly flexible photodetectors were then

fabricated, which demonstrated optimized

performance with fast response time (43 ms) and

high on/off ratio (~170) compared with the device

made of pristine GaP NWs.

2 Experiments

2.1 Synthesis and Characterization of pearl-like

GaP nanowires

Pear-like GaP NWs were synthesized in a horizontal

tube furnace through a CVD process. In a typical

process, GaP power (Alfa Aesar, 99.999% purity),

serving as the source material, was loaded into an

alumina boat and positioned at the center of the tube.

Silicon wafers (100) were placed downstream, about

15 cm away from the GaP power to collect the

deposited products. Prior to heating, the reaction

system was purged with high-purity N2 for 1 h in

order to eliminate the remaining oxygen in the tube.

The furnace was heated from the room temperature

to 1000 oC in 30 min and kept at this temperature for

2 h. During the experimental process, a high-purity

N2 flow of 100 sccm was introduced into the reaction

system. After the reaction, the furnace was cooled to

room temperature and a layer of yellow wool-like

product was found on the Si substrate. The

as-synthesized product was characterized by X-ray

diffraction (XRD, X’pert Pro, PANalytical B.V.,

Netherlands), scanning electron microscopy (SEM,

Hitachi S4800) and transmission electron microscopy

(TEM, JEOL JEM-3000F) equipped with an

energy-dispersive X-ray spectrometer (EDS).

Photoluminescence (PL) spectrum was collected at

room temperature with an HORIBA Jobin Yvon

LabRAM Spectrometer HR 800 UV with a He-Cd

laser line at 514 nm as the excitation source.

2.2 Fabrication of field-effect transistors (FETs) and

hybrid photodetectors

Individual pearl-like GaP NW devices were

fabricated according to our previous reported

technique [15]. Briefly, the GaP NWs were first

dispersed in isopropanol and then dropped on a

thermally oxidized Si substrate covered with a 300

nm SiO2 layer. After the wafer was dried in air, UV

lithography, thermal evaporation and lift-off

processes were carried out to pattern the Cr/Au drain

and source electrodes (10 nm/100 nm) on both ends

of the NWs. PCBM (60 mg) was first dissolved in 4

mL of chloroform. A GaP NWs solution (100 μL,

about 80 mg mL-1) and a solution of PCBM (200 μL)

were mixed to from the final solution. To fabricate

the rigid photodetector, the mixed solution with

PCBM and GaP NWs was first dropped on a SiO2

(300 nm)/Si wafer and formed a hybrid film. Parallel

silver wires with an interval of 1 mm were fixed on

the film with silver paste as the binder. Then, the

devices were heated at 100 oC in a vacuum for 2 h to

solidify the silver paste. Similarly, the pure pearl-like

GaP NWs photodetectors on rigid SiO2/Si wafer were

fabricated. Meanwhile, the flexible photodetectors

can be also constructed on the flexible substrate (PET,

common sellotape and PDMS) by using a similar

process for the rigid device.

2.3 Electrical transport and photoresponse

measurements

The electrical transport measurements of single GaP

NW devices were conducted by the four-probe

station with a semiconductor characterization system

(Keithley 4200-SCS). The incident power of the light

was measured by an Ophir NOVA power meter.

Monochromatic light from a source composed of a

tungsten lamp (300 W) and a monochromator

(WDG15-Z) was focused and guided onto the

semiconductor NW. All measurements were

performed in air and at room temperature.

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

3 Nano Res.

3 Results and discussion

The representative morphology of the product was

characterized by a SEM and the coresponding SEM

images were shown in Figure 1a-b. Figure 1a shows

the low-magnification SEM image of the product,

which reveals that the products are mainly composed

of pearl-like NWs with length ranging from several

to several tens of micrometers. The yield of the

pearl-like nanostructures is estimated to be about

90%. Figure 1b shows the high-magnification SEM

image of the as-grown product. It can be seen that,

for a single pearl-like NW, the diameter of the bulb

parts is in the range of 100-400 nm, and the diameter

of the trunk is about 150 nm.

The crystal structure of the as-synthesized product

was characterized by X-ray diffraction (XRD), as

shown in Figure. S1. All diffraction peaks can be

indexed to pure zinc blende (cubic) GaP (JCPDS No.

32-0397). No peaks from Ga2O3 or other crystalline

phase were detected, indicating the formation of

pure GaP phases. Figure 1c shows a typical PL

spectrum of the as-synthesized GaP product. Only a

sharp peak is observed and located in ~548 nm,

corresponding to the band-gap emission of GaP

(Eg=2.26 eV), which is in consistent with the literature

value [16].

Figure 1. (a-b) low-magnification and high-magnification SEM images, (c) PL spectrum, and (d) TEM image of the as-grown

GaP product. (e,f)HRTEM images of the corresponding parts shown in 1e and 1f. The inset in (f) shows the corresponding

SAED pattern of the as-prepared GaP NW.

To further get information about the detailed

microstructure of the pearl-like GaP nanowires, TEM

characterization was performed and the

corresponding results were shown in Figures 1d-f.

Figure 1d depicts a low-magnification TEM image of

a single GaP NW, which clearly revealed that the NW

is actually made of a straight nanowire (trunk park)

wrapped periodically with olive-shaped bulbs along

the whole trunk. The trunk NW has a diameter of

~150 nm, whereas the maximum diameter of the

bulbs is about 380 nm. The corresponding

high-resolution TEM (HRTEM) images from different

regions of the NW are shown in Figures 1e-f. Figure

1e is a lattice resolved HRTEM image taken from the

bulb part. The marked adjacent plane spacings are

both 0.315 nm, corresponding to the (111) lattice

planes of cubic GaP phase. A selected-area electron

diffraction (SAED) pattern and a HRTEM image

taken from the trunk part are shown in Figure 1f. As

can be seen, the spacings between two adjacent plane

have the same value of ~0.315 nm, which is also

assigned to the (111) lattice plane of cubic GaP

structure. The result indicated that the trunk NW has

preferred grown direction along the [111] orientation.

A SAED pattern of the trunk part is shown in the

inset, which further verifies its single crystal nature.

The corresponding EDS spectrums of both the

wrapped bulb part and the trunk part are depicted in

Figure S2a-b, respectively. From the curves, it can be

seen clearly that both parts are composed of only Ga

and P elements with a composition of ca. 1:1, close to

the stoichiometry of GaP. In the spectrum, signals

from C and Cu elements are from the TEM grid. And

the signal from O element (the inset in Figure. S2a)


4 Nano Res.

may be from the surface oxide layers. On the basis of

the above elemental analysis, the products are

actually pearl-like GaP NWs composed of GaP trunk

NWs decorated with GaP bulbs.

Figure 2. (a) Ids-Vds curves at various Vgs, (b) Ids-Vgs curve measured at Vds=10V of single GaP NW based back-gate FET. The

inset is the SEM image of the device with a channel length of about 3 µm. (c) I-V curves and (d) reproducible on/off

switching (blue curve) of the hybrid PCBM :GaP film based device on Si/SiO2 substrate. The reproducible on/off switching

of pure GaP film was also shown (red curve).

Since the growth of the GaP NWs is via a one-step

process without the use of catalyst, the growth can be

proposed to be governed by a self-organization

vapor-solid (VS) process according to previous report

[17]. The whole growth process can be clearly

expressed in Figure S3. At high reaction temperature,

the mixed Ga and P vapor can be obtained by the

decomposition of GaP power and transferred by the

carrier high-purity N2 gas to a low-temperature

region. And they aggregate and deposit on the

surface of the Si wafer as a nuclei to form a trunk

nanowire. Meanwhile, the Ga vapor has a faster

transfer speed to the low-temperature region under a

high reaction temperature and form a viscous liquid

because of its lower melting point (29.8 oC).

Afterwards it reacts with the P vapor to form GaP

nanoparticles due to surface tension and deposit on

the surface of the firstly formed GaP NW [18-20].

With the increase of reaction time, the pearl-like GaP

NWs are formed.

In order to investigate the electronic transport

properties of the as-grown pearl-like GaP NWs,

single NW based FETs were first fabricated with the

common back-gate configuration on 300 nm

SiO2-coated Si wafer via a traditional lithography

process. The parallel Cr/Au (10/100 nm) films were

used as the source/drain electrodes and deposited on

both ends of the NWs. The inset in Figure 2a depicts

a SEM image of a single GaP device. A single

pearl-like GaP NW was observed to be pinned under

two Cr/Au electrodes. The channel width of the

device is about 3 μm. Figure 2a shows the drain

current (Ids) versus source-drain voltage (Vds) curves

of the device measured at different gate voltages (Vgs,

from -10 to 10 V). It can be seen clearly that the

conductance of the pearl-like GaP NW gradually

increases with decreased gate voltages ranging from

-10 to 10 V, indicating a typical p-type

semiconducting behaviour. The drain current (Ids)

versus gate voltage (Vgs) curves of the device was

also measured for the same device at a drain bias of

10 V and the result was shown in Figure 2b. At the

identical voltage, the drain current decreased when

the gate voltage varied from -10 V to 10 V, further

revealing that the pearl-like GaP NWs are typical

p-type semiconductors. Meanwhile, the threshold

voltage (Vth) of 3.4 V and On/Off ratio of ~102 can be

determined by extrapolating the linear regain of the

Ids-Vgs curve in Figure. 2b.

Recently, considerable attention has been focused

on organic-inorganic hybrid photodetectors due to

the fact that they can combine the merits of organic


5 Nano Res.

semiconductor, such as large scale production

process with low cost, easily-tunable functionality

and the exceptional mechanical flexibility, and that of

the inorganic material, including superior intrinsic

carrier mobilities and broad spectrum absorption

capability. Therefore, hybridizing organic and

inorganic materials may lead to high performance

devices with versatile functions and excellent

flexibility [6,7,10,21]. In order to fabricate hybrid

organic/inorganic photodetectors, the pearl-like GaP

NWs were first mixed with PCBM to form a hybrid

film on a SiO2/Si wafer. Parallel silver electrodes with

an interval of 1 mm were then deposited on the film

to construct a prototype device. Figure 2c shows the

I-V curves of the hybrid device in dark and under

illumination with 550 nm light of different intensities.

It can be conspicuously observed that, at the same

voltage, the photocurrent increases gradually with

the increased light intensities, which can be

attributed to change in the photon intensity of the

hybrid organic-inorganic devices. Light can be

absorbed through the whole thickness of the device

and that of both types of charge carrier run within

the device. The light intensity dependence of the

photocurrent measured at a bias of 2 V is depicted in

Figure S4. The corresponding dependence of the

photodetector on light intensity can be fitted to a

power law, I =APθ [22,23]. By fitting the measured

data in the curve, the corresponding function is I~P0.77,

revealing that the photocurrent exhibits good

dependence on light intensity, which further

indicates the superior photocurrent capability of the

hybrid photodetector.

The high photosensitivity of the hybrid device

based on PCBM:GaP pearl-like NW hybrid film is

further confirmed by photocurrent measurements on

the device at the on/off states by periodically turning

on and off 550 nm light with a power intensity of 3.15

mW/cm2 at a bias of 2 V, as shown in Figure 2d. From

the curves, the photocurrent increases rapidly and

reaches steady state at the “ON” state upon light

illumination, and then decreased quickly to the

“OFF” state after the light was turned off, suggesting

the excellent stability and reproducibility of the

hybrid device. For the hybrid device, the current was

only 2.2 nA in the dark. However, the current could

approach 374 nA at an incident light intensity of 3.15

mW/cm2 and a bias voltage of 2.0 V. The on/off

switching ratio is about 170. Meanwhile, the rise time

of the hybrid device is about 43ms (shown in Figure

S4b). In contrast, devices based on pure GaP

pearl-like NWs showed quite low photocurrent of

228 nA at a bias voltage of 2.0 V, an enhancement of

about 40 times compared with its dark current of 5.7

nA. Meanwhile, the dark current (2.2 nA) in the

hybrid device at an applied voltage of 2 V was much

lower than that of pure pearl-like GaP NWs (5.7 nA)

at the same condition, which could be attributed to

difficult charge transportation through the interface

of the PCBM and the pearl-like NWs without light

illumination. The result is in agreement with a

previously reported hybrid photodetector [7,10].

These results demonstrate that the PCBM and GaP

pearl-like NW hybrid film have enormously potential

applications as highly photosensitive detectors and

efficient photoswitches.

The above results demonstrate that the hybrid

device on rigid SiO2/Si substrate has an excellent

stability, reproducibility, and a fast detection time.

More importantly, it shows much improved

photocurrent and enhanced photoresponse

properties. This fact can be rationalized as following.

It is known that, due to high surface-to-volume ratio

of NWs, particularly for the pearl-like nanostructure,

trapping at the surface states drastically influence the

transport and photoconduction properties. For a

p-type NWs film based device, upon illumination

with a photo energy above the band-gap of GaP

(Eg~2.26 eV), electron-hole pairs are photogenerated

and electrons can be readily trapped at the NW

surface, leaving unpaired holes behind, which results

in an increase of the hole concentration, and then

leads to the increase of the conductivity of the GaP

NW [4]. Specially for the PCBM:GaP hybrid device,

the interface of the hybrid device plays a key role in

charge dissociation and transportation. It is generally

known that exciton dissociation can occur efficiently

at the two semiconductors mixed together in a

blended film, e.g. the system of an inorganic

semiconductor and an organic conjugated polymer in

a hybrid film [24-26]. The photoexcited electrons can

be readily transferred to the material with the higher

electron affinity, while the hole can be accepted by

the material with the lower ionization potential. Due

to the fact that GaP has a relatively low electron

affinity of 1.89 eV [27], while PCBM has a LUMO


6 Nano Res.

level at around 4.3 eV [28], the possible band

alignment can be schematically plotted as the inset of

Figure S5. In this system, the photoexcited electrons

can be readily transferred to PCBM, leaving holes in

the GaP NW for photoconduction. This unique

configuration further improves the efficiency of

spatial separation of electron hole pairs leading to

higher photocurrent and prolonged photocarrier life

time.

Figure 3. Photoresponse properties of the flexible hybrid devices on PET substrate. (a) Schematic illustration of the hybrid

photodetector. The insets are the digital image and SEM image of the hybrid device. (b) Current versus voltage plots of the

hybrid device measured at room temperature in dark and under illumination with 550 nm light of different intensities. (c)

Photocurrent versus light intensity plot at a bias of 2 V. The corresponding function is I~P0.7. (d) Photocurrent versus time

plot of the device under illumination with 550 nm light at a bias of 2 V. (e) Zoom-in view of middle cycle at a bias of 2 V.

The light intensity is kept constant at 3.15 mW/cm2.

On the other hand, as the photoconductivity of

pure PCBM may affect the device performance,

photoresponse characteristics of the device made

from pure PCBM is also studied and shown in Figure

S6 in the supporting information. Notably, the dark

current (about 0.8 nA) in the pure PCBM device at an

applied voltage of 2V is much lower than that of pure

GaP NWs film (about 5.7 nA) and hybrid device

(about 2.2 nA) at the same condition. The result is in

agreement with previously hybrid device based on a

P3HT:PCBM blend [26]. Meanwhile, for the pristine

PCBM device, the photocurrent of 550 nm light

illumination was relatively low and about 4.3 nA,

which is much lower than the photocurrent of pure

GaP NWs film device (227.6 nA , shown in Figure 4d)

and the hybrid device (373.8 nA , shown in Figure

4d). This can be explained by much lower carrier

mobility in PCBM (0.21 cm2/Vs) as compared with

that in GaP NWs. In addition, in our hybrid system,

the GaP NWs are highly dispersed in the PCBM

matrix, forming a 3D interconnected network. The

unique structure results in a large interface area for

charge separation. Therefore, long-lived charge

separation and high transportation might be


7 Nano Res.

achieved in the hybrid device. These results imply

that the performance enhancement of the hybrid

device is primarily contributed by the formation of

the junction interface and the favorable alignment of

the conduction band to prolong the carrier life time.

To explore the reason for the enhanced

photoresponse property, the UV-vis absorption

spectrum of a pure GaP NWs film, PCBM film and

PCBM:GaP NWs hubrid film (≈weight ratio of 3:5)

were measured and shown in Figure S7 in the

supporting information. From the spectrum, it can be

observed that the pure PCBM film depicts a main

absorption in the UV region with the peak at around

330 nm, and the pure pearl-like GaP film shows a

stronger absorption at the wavelength of 370 nm.

When pearl-like GaP NWs are mixed with PCBM, the

PCBM: GaP NWs hybrid film has the advantages of

both PCBM and GaP NWs and significantly broadens

the absorption spectra in the range of 320-450 nm,

which will be beneficial to efficient photo absorption

and exciton generation. These results indicate that

synergy effect made a tremendous contribution to

the enhanced photoresponse of the hybrid film.

After getting information about the electric

transport properties of the GaP NWs and the

photoresponse behavior of the hybrid PCBM:GaP

film, flexible photodetectors were then fabricated on

flexible PET substrate, as demonstrated in Figure 3a.

The as-fabricated flexible device can be operated

under bending state, revealing its excellent flexibility

which can be potentially used in flexible electronics.

The structures of the hybrid film was investigated by

SEM and the corresponding image is shown in

Figure 3a. It can be clearly observed that the

pearl-like GaP NWs were wrapped by the PCBM film,

indicating the good contact between the organic and

inorganic materials, which will benefit the charge

transportation through the interface between PCBM

and GaP NWs, and then improve the photoresponse

of the flexible hybrid device.

Figure 3b shows the I-V curves of the flexible

device when illuminated by light with wavelength of

550 nm and in dark, respectively. Obviously, the

photocurrent increases with the increased light

intensity ranged from 0.32 mW/cm2 to 3.15 mW/cm2,

which consists well with the rigid device on Si

substrate. By fitting the corresponding light-intensity

dependence of the photocurrent plotted in Figure 3c,

the power law function of I~P0.70 is obtained. Figure

3d presents the time-dependent photoresponse of the

flexible device measured by periodically turning the

light with a power density of 3.15 mW/cm2 on and off.

From the curves, we can find that the flexible device

shows superior sensitivity and stability to visible

illumination with the current on/off ratio of 60 at a

bias of 2.0 V. In addition, it is found (Figure 3d) that

the flexible device exhibited a dark current of 0.24 nA

and a photocurrent of 14.4 nA. Compared with the

hybrid device on rigid substrate (shown in Figure 2),

it is obviously seen that the photocurrent is much

smaller, which may attributed to the worse contact

between the pearl-like NWs and flexible PET

substrate, which fits well with the previous reports

on flexible devices [10,11]. Figure 3e shows a

individual photoresponse cycle obtained from the

time-dependent measurement in Figure 3d. The rise

time and decay time are found to be about 0.3s and

0.34s, respectively, which is comparable to that of the

device on rigid substrate.

Figure 4. I-T curves of the flexible hybrid devices on PET

substrate bent with various curvatures under a bias voltage

of 2V. The upper insets are the corresponding digital

photographs of the device under five bending states. The

lower inset show the I-V curves of the flexible hybrid

device on PET substrate without bending and after 20, 40,

60, 80, 100 and 120 cycles of bending, respectively.

In order to accommodate practical application of

the flexible photonic devices, not only the excellent

photoresponse characteristic but also the stability

and reliability is essentially needed. To get the

corresponding information, the flexible device was

fixed on two X-Y mechanical stages with a moving

step of 1 μm. Each end of the device was placed on


8 Nano Res.

one stage. By adjusting the distance of the adjacent

stages, the bending curvature of the hybrid device

was precisely controlled. The electrical stability of the

flexible device based on PCBM:GaP hybrid film was

tested at various bending curvatures, accordingly. As

shown in Figure 4, five different bending stats of the

flexible device were recorded and labelled as state I,

II, III, IV, and V, respectively. As observed, the current

flow through the flexible device nearly kept

unchanged at five different states (the upper insets in

Figure 4), revealing that the conductance of the

hybrid film is hardly influenced by external bending

stress. In addition, the I-V curves of the flexible

device before and after bending for several cycles are

shown in lower insets of Figure 4. Bending of the

flexible device from states I to V followed by

releasing it back to state I was considered as one

cycle. From the curves, it can be seen that, compared

with the conductance of the device without bending

(the lower left inset in Figure 4), the conductance

endurance of the hybrid device (the lower right inset

in Figure 4) almost remains constant even after 20, 40,

60, 80, 100 and 120 cycles of bending, revealing the

good folding endurance of the flexible device. These

results demonstrate excellent electrical stability and

mechanical flexibility of the flexible PCBM:GaP

hybrid device.

Figure 5. Photoresponse properties of the flexible hybrid devices on (a-d) common sellotape and (e-f) PDMS substrate. (a)

Current versus voltage plots of flexible photodetector on sellotape substrate at different intensities. The upper left inset: the

digital image of the device. (b) Photocurrent versus light intensity plot at a bias of 2 V of the device on sellotape substrate.

The corresponding function are I~P0.72. (c) Photocurrent versus time plots of the device under illumination with light of

various wavelengths. (d) Zoom-in view of middle cycle at a bias of 2 V when illumination with a 550 nm light. (e) I-V plots

of flexible device on PDMS substrate in dark and under 550 nm light illumination. The upper left inset: Schematic

illustration of the device. (f) I-T plots of the flexible device on PDMS substrate at a bias of 2 V. The light intensity is kept

constant at 3.15 mW/cm2.

Highly flexible photodetectors were also fabricated on other flexible substrates to demonstrate the


9 Nano Res.

feasibility of the current hybrid PCBM:GaP films.

Inset in Figure 5a shows the digital image of a

flexible device on sellotape, which was rolled into a

cylinder, indicating the excellent flexibility of the

device. Figure 5a exhibits a typical I-V curves of the

device measured under dark and a 550nm light

illumination at different intensities, respectively. It is

clearly shown that, at identical voltages, the

photocurrent of the device increases as the intensity

increases, which is in good agreement with the result

on either Si/SiO2 substrate (Figure 2) or PET substrate

(Figure 3). The corresponding light-intensity

dependence of the photocurrent can be fitted with

the power law, I~P0.72, also revealing excellent

photocapture in the hybrid film. Furthermore, the

reproducible on/off switching of the flexible device

on common sellotape (Figure 5c-d) further

demonstrates the superiority of the organic-inorganic

hybrid photodetector with a fast rise time (0.58 s) and

decay time (0.81 s). Flexible device was also

fabricated on polydimethylsiloxane (PDMS)

substrate and the corresponding results were

depicted in Figure 5e-f. The device also exhibits good

stability and reproducibility, and is sensitive to green

light (550 nm). All the above results indicate that all

the flexible device based on the PCBM:GaP NWs

hybrid film on different flexible substrates have

excellent stability, reproducibility, and a fast

detection time, which will exhibit good advantage for

application in the next generation high-sensitivity

and high-speed large scale organic-inorganic

photodetectors and photoswitches.

4 Conclusions

In conclusion, pearl-like GaP NWs were

synthesized via a simple CVD method, which were

mixed with PDMS to act as active materials for

highly flexible hybrid photodetectors on various

flexible substrate. Compared with the devices made

of either pure GaP NWs or PCBM, the hybrid device

exhibited an enhanced photoresponse characteristic

such as a fast response, increased photocurrent and

high photoresponse ration Besides, all the fabricated

flexible devices showed excellent flexibility, good

folding strength and high electrical stability and high

sensitivity to visible light. Our results demonstrate

that the organic-inorganic hybrid photodetectros

have promising potential for future application in

next generation of optoelectronic devices.

Acknowledgements

This work was supported by the National Natural

Science Foundation (91123008, 61377033), the 973

Program of China (No.2011CBA00703).

Electronic Supplementary Material: Supplementary

material (XRD pattern, EDX spectra, schematic

diagrams of the growth process of GaP nanowires;

photoresponse behavior and band gap diagrams of

the PCBM:GaP hybrid photodetectors;

photoresponse behavior of pure PCBM.) is available

in the online version of this article at

http://dx.doi.org/10.1007/s12274-***-****-*

(automatically inserted by the publisher). References

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Nano Res.

Electronic Supplementary Material



Gui Chen,† Xuming Xie,† and Guozhen Shen ()

Supporting information to DOI 10.1007/s12274-****-****-* (automatically inserted by the publisher)

FIGURE S1. XRD pattern of the as-grown pearl-like GaP nanowires.


Nano Res.

FIGURE S2. EDS spectrum of the e, f part shown in Figure 1d.

FIGURE S3. Schematic diagrams of the growth process of the pearl-like GaP nanowires.


Nano Res.

FIGURE S4. (a). Photocurrent versus light intensity plot at a bias of 2 V. The corresponding function is I~P0.77.

(b). Single light on/off cycle transient response of the hybrid device at a bias of 2 V with light intensity of 3.15

mW/cm2.

FIGURE S5. Band diagrams of the PCBM:GaP hybrid film based photodetector.


Nano Res.

FIGURE S6. Photoresponse characteristics of a device made from a pure PCBM film. (a). I-V curves of the

device in dark and under 550 nm green light illumination. (b). I-T curves of device under 550 nm illumination

measured for light-on and light off conditions at a 2 V applied voltage. The light intensity is kept constant at

3.15 mW/cm2.

FIGURE S7. UV-vis absorption spectra of a pure GaP NWs film (black), PCBM film (blue) and PCBM:GaP NWs

hybrid film (red) (≈weight ratio of 3:5).

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