Science Fair Report 2015

2015

Kiana Lee

Niles North High School

3/7/2015

Characterization of Ruthenium and Organic

Based Dye Sensitized Solar Cells with Time

Dependent Dye Loading

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Table of Contents Table of Contents ........................................................................................................................................ 1

Acknowledgements ..................................................................................................................................... 2

Purpose ........................................................................................................................................................ 3

Hypothesis and Rationale ........................................................................................................................... 4

Review of Literature ................................................................................................................................... 5

Materials .................................................................................................................................................... 14

Procedure ................................................................................................................................................... 17

Variables .................................................................................................................................................... 23

Results ........................................................................................................................................................ 24

UV-vis Spectrometry Data ...................................................................................................................... 25

Solar Conversion Efficiency Data ........................................................................................................... 27

Electron Lifetime Data ............................................................................................................................ 38

Incident Photon-to-Current Efficiency (IPCE) Data ............................................................................... 43

Discussion and Analysis ............................................................................................................................ 46

Conclusion ................................................................................................................................................. 51

Appendix .................................................................................................................................................... 53

Literature Cited ........................................................................................................................................ 57

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Acknowledgements

First and foremost, I would like to thank William Hoffeditz and Monica So, graduate

students in the department of Chemistry at Northwestern University. William Hoffeditz and

Monica So are both currently completing their Ph.D.’s in Chemistry, and belong to the Hupp

Research Group at Northwestern University. With their guidance and dedication, I was able to

complete a higher-level project than I have in previous years. I would also like to thank Professor

Dick Co of Northwestern University for allowing me to work in his lab and for supporting my

interest in independent research. Additionally, I would like to thank the Argonne-Northwestern

Solar Energy Research (ANSER) Center for providing the funding necessary to complete my

research. I would also like to thank Michael Katz, a Post-Doctoral Fellow at Northwestern

University, for supervising me in the lab whenever Monica and Will were unable. I would also

like to thank my sponsor, Ms. Christine Camel, and my parents for their encouragement and

support.

Special Note

Although Professor Dick Co, Monica So, and William Hoffeditz have been my mentors

and supervisors at Northwestern University, all the data was collected and the entire paper was

written by myself.

For Further Inquiry Please Contact:

Dick T. Co, Ph.D.

Director of Operations and Outreach

Research Associate Professor of Chemistry

Department of Chemistry

Northwestern University

2145 Sheridan Road

Evanston, IL 60208-3113

Ph: 847-467-3396;

Fax: 847-467-1425

Email: [email protected]

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Purpose

There are two fundamental purposes in which this experiment is based. The first is to

determine the optimal dye loading time of nanoparticles to construct the most efficient dye

sensitized solar cell. The second is to determine the factors that affect solar conversion efficiency,

and how dye structure affects solar cell performance.

Through these studies we will learn how to improve dye sensitized solar cell construction,

and small innovations are necessary to move dye sensitized solar cell technology forward. In order

to become the primary candidate for an alternative fuel source dye sensitized solar cell efficiency

needs to improve to a level that is competitive with silicon solar cells, and eventually fossil fuels.

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Hypothesis

Hypothesis I:

If dye sensitized solar cells (DSSCs) are dye loaded for 1 hour, 3 hours, 5 hours, and

overnight, then the solar conversion efficiency will increase with increased dye loading time.

Hypothesis II:

If dye sensitized solar cells (DSSCs) are dye loaded with Carbazole, JK2, N719 and

Ru(dcb)(bpy)2 dye, then the extinction coefficient of a given dye will not be the sole factor in

determining solar conversion efficiency.

Hypothesis III:

If dye sensitized solar cells (DSSCs) are dye loaded with Ruthenium and Organic Dyes,

and there are multiple factors affecting solar cell performance, then dye structure will dictate how

electrons travel through the beneficial and parasitic kinetic processes in a dye sensitized solar cell

(DSSC).

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Review of Literature

Introduction

Global environmental concerns are arising over our excessive reliance on fossil fuels,

which supply most of the world’s electricity (Yum, Chen, Grätzel, & Nazeeruddin, 2008). In

2000, the mean global energy consumption rate was 13 tera watts, which is equivalent to 13

trillion watts (Hagfeldt, A., Boschloo, G., Sun, L., Kloo, L., & Pettersson, H., 2010). These

astonishingly large numbers will only increase in the years to come with the population growth

rate growing exponentially, and in 2050, the projected global consumption rate is 28 tera watts

(28 trillion watts) (Hagfeldt 2010). With these staggering rates of energy consumption that are

only increasing, a number of challenges have arisen such as increasing CO2 , certain countries

having a monopoly over fossil fuel supplies, and environmental implications (Yum 2008). An

alternative fuel source from renewable energy could be the solution to all these problems arising

from excessive use of fossil fuels. Solar energy is an advantageous candidate for an alternative

fuel source because it is low cost, and the sun can sustain the infinitesimally large global energy

consumption rate. However, in order for solar energy to become the prime candidate for an

alternative fuel source efficiency needs to be improved.

Solar Photovoltaics

Solar Photovoltaics are a technology that converts sunlight into electricity through light

absorbing materials connected to an external circuit. To drive excited electrons through an

external circuit, the photovoltaic cell needs to have some asymmetry (Nelson, 2003). The

effectiveness of a photovoltaic device is mainly dependent on the type of light absorbing

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materials used, and the way in which the light absorbing materials are connected to the external

circuit (Nelson, 2003).

The basic building block of solar photovoltaics is the solar cell (Nelson, 2003). In a

simple electric circuit, the solar cell can take the place of a battery (Nelson, 2003). The open

circuit voltage (Voc) is the voltage developed when the terminals are isolated (infinite load

resistance (Nelson 2003). The open circuit voltage (Voc ) is the maximum voltage available from

a solar cell, and this occurs at zero current. The short circuit current (Jsc) is the maximum current

from the solar cell and occurs when the voltage is zero. The open circuit voltage and short circuit

current are used to determine fill factor. The fill factor (FF) describes the “squareness” of a J - V

Curve (Nelson 2003). The fill factor is defined by the following equation:

The fill factor, short circuit current, and open circuit voltage are used to determine solar energy

conversion efficiency. Solar energy conversion efficiency (η) is the percentage of sunlight

converted to electricity. Solar conversion efficiency is defined by the equation:

Dark current is the current that flows across the device under an implied voltage in the dark

(Nelson 2003). It is important to understand the role that electron density and electron lifetime

(τn) play in photovoltaic performance in order to comprehend the mechanism of dye sensitized

solar cells (DSSCs) (Ito, S., Humphr y-Baker, R., Liska, P., Comte, P., Péchy, P., Nazeeruddin,

M. K., & Grätzel, M., 2011). Electron life measures how many electrons are collected in the

TiO2 conduction band and transferred into current.

(1)

(2)

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Electron lifetime (τn) is defined by the equation:

where kB is the Boltzmann constant, T is the absolute temperature, q is the positive elementary

charge, and τn is given by the reciprocal of the derivative of the decay normalized by the thermal

voltage (Ito, S., Humphry-Baker, R., Liska, P., Comte, P., Péchy, P., Nazeeruddin, M. K., &

Grätzel, M., 2011). Incident Photon-to-Current Conversion Efficiency is the ratio of the number

of electrons to the number of incident photons collected by the solar cell.

Incident Photon-to-Current Conversion Efficiency (IPCE%) is defined by the equation:

where iph is the photocurrent density generated by monochromatic light with wavelength λ, and

intensity pin.

Dye Sensitized Solar Cells (Third

Generation Solar Cells)

Dye sensitized solar cells are a

fairly new photovoltaic technology as

they were first created in 1991 by

Michael Grätzel, and are regarded as

next generation solar cells because of

their high solar conversion efficiency

and economic benefits (Cheng, Yang,

(3)

Figure 1 Photo of Michael Grätzel, inventor of dye sensitized solar

cells, next to industrial dye sensitized solar cells (Phys.org [online]).

(4)

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Li, Zhang, & Sun 2013). Dye Sensitized Solar Cells are advantageous for their low productions

costs compared with

conventional photovoltaic

technologies (Hagfeldt 2010).

They are also beneficial for their

flexibility, lightweight,

feedstock availability to reach

terawatt scale, applications for

indoors, ability to capture light

from all angles, and design

opportunities, such as

architectural options. Hagfeldt, A., Boschloo, G., Sun, L., Kloo, L., & Pettersson, H. 2010). A

dye sensitized solar cell is composed of five main components: a conductive mechanical support,

a semiconductor film, a sensitizer, an electrolyte, and a counter electrode. To increase conversion

efficiency, the photosensitizer needs to capture as much incident light as possible (Cheng, Yang,

Li, Zhang, & Sun 2013).

In Figure 2, a schematic representation of the operating principles of the interior of a dye

sensitized solar cell. At the center of a dye sensitized solar cell, is the mesoporous oxide layer

composed of a network of TiO2 nanoparticles that have been sintered together to establish

electronic conduction (Hagfeldt 2010). The mesoporous layer is deposited on a transparent

conducting oxide (TCO) on a glass substrate. Fluorine doped tin oxide (FTO) is a commonly

Figure 2 Schematic of the operating principles of a dye sensitized solar

cell (DSSC).

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used substrate coated on the glass (Hagfeldt 2010). The charge transfer dye is attached to the

surface of the nanocrystalline film (Hagfeldt 2010).

A dye sensitized solar cell

begins producing electricity once

light hits the dye since it is the

photoactive material of the DSSC

(Dye Sensitized Solar Cells n.d).

The dye produces electricity by

catching photons of incoming

light, and then uses energy to

excite electrons (Dye Sensitized

Solar Cells n.d). Then, the dye injects the excited electrons into the Titanium Dioxide (TiO2),

and the electrolyte closes the cell so that the electrons are returned back to the dye (Dye

Sensitized Solar Cells n.d). The movement of these excited electrons is what creates the energy

that can be harvested into a rechargeable battery, super capacitor or another electrical device

(Dye Sensitized Solar Cells n.d.).

Photosensitizers

The photosensitizer, also known as the dye, is one of the most critical parts of a dye

sensitized solar cell. Some of the key characteristics a dye should fulfill are: 1) have anchoring

groups (-COOH, -H2PO2, -SO3H, etc.) to strongly bind the dye onto the semiconductor surface,

2) have an oxidized state level that is more positive than the redox potential of the electrolyte in

order for dye regeneration to occur, 3) have an absorption spectrum that covers the whole visible

Figure 3 Schematics of the electron transfer processes in a dye sensitized

solar cell (DSSC).

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region and parts of the near-infrared (NIR), 4) should be photostable, and have electrochemical

and thermal stability (Hagfeldt 2010).

Metal complexes, specifically (Ru(II)) complexes, has shown significant promise because

of their broad absorption spectra and favorable photovoltaic properties (Hagfeldt 2010).

Ruthenium complexes have a relatively long electron lifetime, good electrochemical stability,

suitable excited and ground state energy levels, and broad absorption spectrums (Hagfeldt 2010).

Other than Ruthenium dyes, organic dyes have also gained much popularity among

researchers for their diverse molecular structures that can easily be synthesized and designed,

low cost, and high extinction coefficients (Hagfeldt 2010). Organic dyes with high molecular

extinction coefficients are promising candidates for dye sensitized solar cells because high

molecular extinction coefficients of organic dyes make them ideal absorbers and have

photochemical stability. Organic dyes are also advantageous for their increased open circuit

voltages obtained relative to ruthenium complexes.

Figure 1 demonstrates the molecular structure of the four dyes Carbazole, JK2, N719, and

Ru(dcb)(bpy)2. Carbazole and JK2 are both organic dyes while N719 and Ru(dcb)(bpy)2 are

Ruthenium dyes. Ru(dcb)(bpy)2 is a non-published Ruthenium dye created by William Hoffeditz

at Northwestern University and consists of a carboxyl acid attached to a known Ruthinium

tri(bpy) dye.

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(a)

(b)

(c)

(d)

Figure 4 Molecular structures of organic and Ruthenium photosensitizers. a) Carbazole. b) JK2. c) N719. d) Ru(dcb)(bpy)2.

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Electrolyte

Electrolyte containing I-/I3- (iodide) redox ions is used in dye sensitized solar cells to

regenerate the oxidized dye molecules and hence completing the electrical circuit by mediating

electrons between the nanostructured electrode and counter electrode (Kim, J. H., Kang, M. S.,

Kim, Y. J., Won, J., Park, N. G., & Kang, Y. S. 2004). Cell performance is greatly affected by

the ion conductivity of the electrolyte, which is directly affected by the viscosity of the solution

(Kim 2004). Limitations introduced with electrolytes are due to evaporation, liquid electrolyte

inhibits fabrication of multi cell modules, and due to the leakage of the electrolyte from the dye

sensitized solar cell (Kim 2004).

Interfacial Electron-Transfer Kinetics in Metal Free Organic Dye Sensitized Solar Cells:

Combined Effects of Molecular Structure of Dyes and Electrolytes

An experiment called Interfacial Electron-Transfer Kinetics in Metal Free Organic Dye

Sensitized Solar Cells: Combined Effects of Molecular Structure of Dyes and Electrolytes studied

electron diffusion coefficient, lifetime, and density in the TiO2 electrode of dye sensitized solar

cells (Miyashita, M., Sunahara, K., Nishikawa, T., Uemura, Y., Koumura, N., Hara, K., ... &

Mori, S. 2008). They compared the efficiencies of 8 organic dyes and 3 Ruthenium dyes. The

results demonstrated that organic dyes have a longer lifetime when they have larger molecular

size and alkyl chains which leads to a higher short circuit current. Although, none of the organic

dyes had longer lifetimes than the Ruthenium dyes (Miyashita 2008).

Closure

As global environmental concerns increase, and the supply of fossil fuels is rapidly

dwindling the importance of researching alternative fuel sources could never be of more utmost

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importance. Dye sensitized solar cells have the potential to become a prime candidate for an

alternative fuel source due to their low production costs and high conversion efficiencies (Yum

2008). Compared to silicon based solar cells, dye sensitized solar cells are of low cost and ease

of production, have an increased performance with temperature, and possess a bifacial

configuration as they have an advantage for diffuse light, transparency for power windows,

varied color from dye, and outperform silicon solar cells in light and cloudy conditions (Yum

2008). The highest solar conversion achieved by a dye sensitized solar cell is over 11%, and was

constructed with a Ruthenium based dye, TiO2 electrode, and an iodide electrolyte (Miyashita

2008). Small modifications that improve individual components such as improving the short

circuit current density, open circuit voltage, and fill factor by extending the light response of the

sensitizers in the near-infrared spectral region, introducing ordered oxide mesostructures and

controlling the interfacial charge recombination by manipulating the cell on the molecular level

are necessary to improve overall efficiency.

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Materials

Nanocrystalline TiO2 Electrode

Flourine Doped Tin Oxide (FTO)

Glass Cutter

Scribe

Pliers

Dog Dish

Sonicator

Alconox

Deionized Water

EtOH

UV-O3

Atomic Layer Deposition

TiO2

Nanoparticles

Scotch Brand Tape

Hole Puncher

Stainless Steel Razor Blade

Dyesol Transparent Terpineol Paste

Oven

Dye Chemicals and Materials

5.6 mg of Carbazole

5.4 mg of JK2

5.3 mg of Ru(dcb)(bpy)2

5.4 mg of N719

Chloroform

Tetrahydrofuran

Acetonitrile

Ethanol

Lab Balance

Plastic Square Dishes

Stainless Steel Tweezers

Permanent Marker

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UV-vis Spectrometry

0.458 M Carbazole Dye

0.732 M JK2 Dye

0.454 M N719 Dye

0.561 M Ru(dcb)(bpy)2 Dye

Automatic Pipettes

Glass Screw Bottles

Glass Beakers

Cuvette

Spectrometer

Chemical Wipes

Computer (Excel)

Dye Loading

0.5 mM Carbazole dye

0.5 mM JK2 dye

0.5 mM N719 dye

0.5 mM Ru(dcb)(bpy)2 dye


Glass Screw Bottles

Pt Electrode

Drill

F-SnO2

0.1 M HCl

EtOH

Acetone

Isopropanol

Ethanol

5 mM H2PtCl-6

Dye Sensitized Solar Cell Assembly

25 um Ionomer Surlyn 1702 (Dupont)

TiO2

Hot Plate

Plastic Tweezers

Hydrogen Gas Pump

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Sandpaper

F-SnO2 Electrodes

Silver Epoxy Paste

Tin Wires

Oven


Iodide/Triiodide (I3/I-) Electrolyte

Glass Cover Slides

Soldering Iron

Vacuum Desiccator

Chemical Wipes

Hydrogen Gas Pump

Measuring Dye Sensitized Solar Cells

Potentiostat

Computer (Excel)

General Safety Materials

Goggles

Plastic Gloves

Lab Coat

Close Toed Shoes

Pants

**No Skin May be Exposed while Performing the Experiment**

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Procedure

Nanocrystalline-TiO2 Electrode

1. A full sheet of Fluorine Doped Tin oxide (FTO) glass was cut into 0.25 cm2 squares using

a glass cutter, pliers, and scribe.

2. Fluorine Doped Tin oxide (FTO) glass squares were then washed in a dog dish using

Alconox soap and deionized water.

3. After the Fluorine Doped Tin oxide (FTO) glass squares were washed, they were sonicated

for 25 minutes, and rinsed with water and EtOH, and treated with UV-O3 treatment for 18

minutes.

4. A blocking layer of TiO2 must be created by an Atomic Layer Deposition (ALD).

5. To place nanoparticles, Scotch brand tape was first hole punched to achieve an electrode

area of 5mm x 5mm.

6. Fluorine Doped Tin oxide (FTO) glass squares were then placed on a glass sheet evenly

spaced in rows, and held in place with the hole punched Scotch brand tape.

7. Dyesol purchased transparent terpineol paste was placed on the edge of the holes and

excess was doctor bladed with a razor blade in one smooth quick movement.

8. After approximately three minutes, the tape was removed and the Fluorine Doped Tin

oxide (FTO) glass squares were dried in a drying oven for six minutes at 125oC.

9. The cells were then gradually heated at 325ºC for 5 minutes, 375ºC for 5 minutes, 450º C

for 15 minutes.

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Dyes

1. Dissolved 5.6 mg of Carbazole in

chloroform to achieve a 0.458 M

solution of Carbazole Dye.

2. Dissolved 5.4 mg of JK2 in

tetrahydrofuran to achieve a 0.732

M solution of JK2 dye.

3. Dissolved 5.3 mg of Ru(dcb)(bpy)2

in acetonitrile to achieve a 0.561 M solution of Ru(dcb)(bpy)2 dye.

4. Dissolved 5.4 mg of N719 in ethanol to achieve a 0.454 M solution of N719 Dye.

5. The stock for each of the 4 dyes was diluted in ratios of 1 to 10, 1 to 20, 1 to 30, 1 to 40,

and 1 to 50 to obtain 5 points for UV-vis measurements.

6. For each dye, absorbance was plotted as a function of concentration to determine the

wavelength in which the peak absorbance was reached.

7. Extinction coefficients were calculated by finding the slope of the points in an Absorbance

vs Concentration at the peak wavelength plot.

Dye Loading

1. After cooling to 80ºC immerse electrode in 0.5 mM of either Carbazole, JK2, N719, or

Ru(dcb)bpy in 1:1 acetonitrile:tert-

butyl alcohol (EtOH also works)

and kept at room temp in time

Figure 5 Ru(dcb)(bpy)2 dye solution, N719 dye solution, JK2 dye

solution, and Carbazole dye solution used to dye load dye sensitized

solar cells.

Figure 6 Dye loaded dye sensitized solar cells with Ru(dcb)(bpy)2,

N719, Carbazole, and JK2 dyes.

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increments of either 1, 3, 5, or 24 hours. Dye solution should be sonicated and filtered to

ensure solution is fully saturated.

2. Remove electrode from solution and quickly rinse with acetonitrile. Dry under H2 stream.

Pt Electrode

1. For the Pt electrode, a hole was drilled in 15ohm/sq F-SnO2, and then sonicated in soap.

2. F-SnO2 was the washed with water and 0.1M HCl solution in EtOH (~1 mL conc. HCl in

100ml) and sonicated in acetone bath for 10 minutes.

3. Residual organic contaminants were removed by heating in air for 15 min at 400ºC.

4. Pt catalyst was deposited by coating with a ~0.5 drop/cm2 of 5mM H2PtCl¬6 in

isopropanol (or ethanol). They were then quickly tilted to

spread and let dry without breeze for 5 minutes.

Solar Cell Assembly

1. To assemble the cells, they were first sandwiched with 25

um ionomer Surlyn 1702 (Dupont) between electrodes.

The aperature should be 2 mm larger than that of TiO2

area and width of 1mm.

2. To sandwich the cells, the sample was first aligned such

that electrolyte hole was not directly over active area.

Figure 7 A dye sensitized solar cell

sandwiched with surlyn.

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3. Then, once the cells were aligned correctly over the

electrolyte hole, the cells were put on a hot plate at 130ºC for

3-5 minutes while significant pressure was applied with

tweezers to seal the cells.

4. Sandpaper was then used to lightly scrape the edge of F-SnO2

electrodes.

5. Distance is importance as sheet resistance is an issue but it is

crucial not to short the cell by connecting electrodes! Epoxy

must then be mixed in equal ratios and stirrer for 2 minutes.

6. Silver epoxy and wires were then applied to both sides of the

cells, and the cells were then placed in the oven for 15-25 minutes at 100ºC.

7. Silver epoxy and wires were then applied to both sides of the cells,

and the cells were then placed in the oven for 15-25 minutes at

100ºC.

8. Iodide electrolyte was then prepared, and the electrolyte solution

was placed in excess to cover the hole in the cells.

9. The cells were then placed in a vacuum desiccator to draw the

electrolyte into the TiO2 network.

10. To seal the hole, surlyn and cover glass was soldered at 600ºF

with a soldering iron to quickly melt polymer film without dumping excess heat into

volatile electrolyte.

Figure 8 Epoxy paste used for

experiment.

Figure 9 A dye sensitized

solar cell sealed with

electrolyte.

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Measuring

1. A potentiostat was used to take voltage, and

current measurements to make JV curves of

light current and dark currents, and Incident

Photon-to-Current Conversion Efficiency

(IPCE), and electron lifetime plots for the

Dye Sensitized Solar Cells (DSSCs).

2. When taking potentiostat measurements

light intensity was set to 0.2 sun. All

samples required the light switched on then off while measuring photovoltage.

3. The potentiostat was set to collect photovoltage measurements for every 0.001 seconds

over a span 15 seconds (about 25,000 data points collected per solar cell).

Data Calculations

1. Potentiostat will give current and voltage values, and the current density and fill factor

must be calculated for JV curves.

2. Current density was calculated by dividing current by the area of the solar cell (0.25 cm2)

and multiplying that by negative 1,000.

Figure 10 Potentiostat taking measurements from a dye

sensitized solar cell exposed to white light.

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3. Fill factor was calculated by multiplying current density

and voltage and dividing that by the product of the Jsc and

Voc, which were identified by finding the maximums of

the current density and voltage measurements produced

from the solar cell.

4. Efficiency was calculated by multiplying the fill factor, Jsc

and Voc.

5. Photovoltage decay was determined by finding the data

points after the light was turned off and imputing it into

the following equation:

6. Incident Photon-to-Electron conversion Efficiency (IPCE)

was calculated by the following equation:

7. The ratio of backside Incident Photon-to-Electron conversion Efficiency (IPCE) to front

side was then calculated for data analysis comparison.

Figure 11 Potentiostat taking

measurements from a dye sensitized

solar cell exposed to white light.

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Variables

Independent Variables: Type of Dye (Carbazole, JK2, N719, and Ru(dcb)(bpy)2), and Dye

Loading Time of Nanoparticles (1 Hour, 3 Hours, 5 Hours, and 24 Hours).

Dependent Variables: UV-vis Spectrometry will be used to determine extinction coefficients of

Carbazole, JK2, N719, and Ru(dcb)(bpy)2 and their respective absorption spectra. J-V Curves will

be used to determine short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF), and

solar conversion efficiency for each dye sensitized solar cell (DSSC). Electron lifetime plots will

be used to determine photovoltage decay of each dye, and the rate in which electrons are collected

by the TiO2 conduction band and transformed to current. Incident photon-to-current conversion

efficiency (IPCE) will be used to determine how well the dyes can collect photons of light.

Control: Not applicable for this experiment and a comparison will be made among trial groups.

Controlled Variables: Experimenter, procedures followed, area of dye sensitized solar cells (0.25

cm2), type of light used (White Light), type of electrolyte used (I3/I-), type of glass (Fluorine Doped

Tin Oxide), type of blocking layer (Nanocrystalline Titanium Dioxide), location of equipment used

(for Dye Sensitized Solar Cell (DSSC) construction, UV-Vis Spectrometry, JV Curves, Electron

Lifetime, and Incident Photon-to-Current Conversion Efficiency (IPCE)), equipment location, and

software used for data analyses.

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Results UV-vis Spectrometry Data ..........................................................................................................25

Solar Conversion Efficiency Data...............................................................................................27

Electron Lifetime Data ................................................................................................................38

Incident Photon-to-Current Conversion Efficiency (IPCE) Data ...........................................43

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UV-vis Spectrometry Data

The absorption spectra for

Carbazole, in figure 13, demonstrates

that light is most absorbed from 480 nm

to 510 nm. The total range of wavelength

where Carbazole absorbs light is from

400 nm to 600 nm, and almost

no light is absorbed at 650 nm.

The extinction coefficient for

the Carbazole dye is 44,817 M-

1cm-1 and the Beer’s law plot

had an R2 value of 0.9991. The

R2 value suggests that the linear

model of best fit represents

99.91% of the variation in the

data.

Dyes Molar Extinction

Coefficient (M-1cm-1)

Carbazole 44,817

JK2 27,380

N719 14,007

Ru(dcb)(bpy)2 12,142

0

0.5

1

1.5

2

2.5

400 450 500 550 600 650 700 750 800

Ab

sorb

an

ce (A

rb.

Un

its)

Wavelength (nm)

JK2 1 to 50 JK2 1 to 30 JK2 1 to 40 JK2 1 to 20 JK2 1 to 10

Table 12 Extinction coefficients of the four

dyes (Carbazole, JK2, N719, Ru(dcb)(bpy)2).

Values are extrapolated from Figure 1,

Figure, 2, Figure 3 and Figure 4.

y = 27380x + 0.0697

R² = 0.9984

0

0.5

1

1.5

2

2.5

0.00E+00 5.00E-05 1.00E-04

Ab

sorb

an

ce (

Arb

. U

nit

s)

Concentration (M)

Figure 14 UV-Vis absorption spectra of JK2 dye. Dilutions were taken from the stock

solution in ratios of 1 to 10, 1 to 20, 1 to 30, 1 to 40, and 1 to 50. The wavelength with

peak absorbance for all dilutions was plotted in a Beer’s Law plot over concentration

and the slope of that plot denotes the extinction coefficient. The peak absorbance for the

JK2 dye were all found at 481 nm.

.

Figure 13 UV-Vis absorption spectra of Carbazole dye. Dilutions were

taken from the stock solution in ratios of 1 to 10, 1 to 20, 1 to 40, and 1

to 50. The wavelength with peak absorbance for all dilutions was

plotted in a Beer’s Law plot over concentration and the slope of that plot

denotes the extinction coefficient. The peak absorbance for the

Carbazole dye were all found at 485 nm.

0

0.5

1

1.5

2

400 500 600 700 800

Ab

sorb

an

ce (

Arb

. U

nit

s)

Wavelength (nm)

Carbz 1 to 10

Carbz 1 to 60

Carbz 1 to 40

Carbz 1 to 20

y = 44817x - 0.0215

R² = 0.9991

0

0.5

1

1.5

2

2.5

0.00E+002.00E-054.00E-056.00E-05

Ab

sorb

an

ce (

Arb

. U

nit

s)

Concentration (M)

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The absorption spectra for JK2, in figure 14, demonstrates that light is most absorbed from

450 nm to 510 nm for dye sensitized solar cells dye loaded with JK2 dye. The total range of

wavelength where JK2 absorbs light is from 400 nm to 580 nm, and almost no light is absorbed at

600 nm. The extinction coefficient for the JK2 dye is 27,380 M-1cm-1 and the Beer’s law plot had

an R2 value of 0.9984. The R2 value suggests that the linear model of best fit represents 99.84% of

the variation in the data.

The absorption spectra for N719, in figure 15, demonstrates that light is most absorbed

from 500 nm to 550 nm for dye sensitized solar cells dye loaded with N719 dye. The total range

of wavelength where

N719 absorbs light is

from 400 nm to 720 nm,

and almost no light is

absorbed at 750 nm. The

extinction coefficient for

the N719 dye is 14,007

M-1cm-1, and the Beer’s

law plot had an R2 value

of 0.9999. The R2 value

suggests that the linear

model of best fit

represents 99.99% of the

variation in the data.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

400 450 500 550 600 650 700 750 800

Ab

sorb

an

ce A

rbit

rary

Un

its

Wavelength (nm)

N719 1 to 5 N719 1 to 10 N719 1 to 20 N719 1 to 50

y = 14007x + 0.0256

R² = 0.9999

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.00E+00 5.00E-05 1.00E-04

Ab

sorb

an

ce (

Arb

. U

nit

s)

Concentration (M)

Figure 15 UV-Vis absorption spectra of N719 dye. Dilutions were taken from the stock

solution in ratios of 1 to 5, 1 to 10, 1 to 20, and 1 to 50. The wavelength with peak

absorbance for all dilutions was plotted in a Beer’s Law plot over concentration and the

slope of that plot denotes the extinction coefficient. The peak absorbance for the N719

dye were all found at 528 nm.

.

Lee

27

The absorption

spectra for Ru(dcb)(bpy)2,

in figure 16, demonstrates

that light is most absorbed

from 420 nm to 490 nm

for dye sensitized solar

cells dye loaded with

Ru(dcb)(bpy)2 dye. The

total range of wavelength

where Ru(dcb)(bpy)2 dye

absorbs light is from 400 nm to

600 nm, and almost no light is

absorbed at 640 nm. The extinction coefficient for the Ru(dcb)(bpy)2 dye is 12,142 M-1cm-1 and

the Beer’s law plot had an R2 value of 0.9986. The R2 value suggests that the linear model of best

fit represents 99.86% of the variation in the data.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

400 450 500 550 600 650 700 750 800

Ab

sorb

an

ce (

Arb

itra

ry U

nit

s)

Wavelength (nm)

Ru(dbc)bpy 1 to 40 Ru(dbc)bpy 1 to 20

Ru(dbc)bpy 1 to 10 Ru(dcb)bpy 1 to 5

y = 12142x + 0.0012

R² = 0.9986

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.00E+00 5.00E-05 1.00E-04 1.50E-04

Ab

soro

ban

ce (

Arb

. U

nit

s)

Concentration (M)

Figure 16 UV-Vis absorption spectra of Ru(dcb)(bpy) dye. Dilutions were taken

from the stock solution in ratios of 1 to 5, 1 to 10, 1 to 20, and 1 to 40. The

wavelength with peak absorbance for all dilutions was plotted in a Beer’s Law plot

over concentration and the slope of that plot denotes the extinction coefficient. The

peak absorbance for the Ru(dcb)bpy dye were all found at 476 nm.

.

Lee

28

Solar Conversion Efficiency Data

Carbazole DSSCs with Highest Efficiency

Cell Type Jsc (mA/cm2) Voc (V) Fill Factor Efficiency (%)

1 Hour Cell 3 2.607 0.603 0.734 1.152

1 Hour Cell 3 Dark Current -4.08E-04 -0.089 0.323 1.17E-05

3 Hour Cell 1 4.592 0.610 0.725 2.028

3 Hour Cell 1 Dark Current -3.43E-04 -0.084 0.412 1.18E-05

5 Hour Cell 1 5.833 0.615 0.739 2.646

5 Hour Cell 1 Dark Current -0.0004 -0.048 0.947 1.67E-05

24 Hour Cell 1 3.404 0.594 0.697 1.407


JK2 DSSCs with Highest Efficiency


1 Hour Cell 3 0.950 0.571 0.730 0.396


3 Hour Cell 3 0.764 0.547 0.764 0.320


5 Hour Cell 1 0.5418 0.596 0.590 0.190


Overnight Cell 1 0.586 0.561 0.751 0.247

Overnight Cell 1 Dark Current -0.0004 -0.075 0.425 1.20E-05

Table 2 Best solar energy conversion efficiencies for Carbazole DSSCs fabricated with time dependent dye loading.

Table 3 Best solar energy conversion efficiencies for JK2 DSSCs fabricated with time dependent dye loading.

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29

Ru(dcb)(bpy)2 DSSCs with High Efficiency


1 Hour Cell 3 1.173 0.573 0.781 0.525


3 Hour Cell 2 0.475 0.510 0.760 0.184


5 Hour Cell 1 1.165 0.556 0.698 0.452185


Overnight Cell 2 0.567 0.510 0.751 0.217


N719 DSSCs with Highest Efficiency

Cell Type Jsc

(mA/cm2)

Voc (V) Fill

Factor

Efficiency

(%)

1 Hour Cell 2 3.833 0.683 0.653 1.710


3 Hour Cell 2 Darker 4.409 0.667 0.461 1.357


5 Hour Cell 1 4.574 0.664 0.764 2.322


Overnight Cell 4 3.791 0.681 0.796 2.056


Table 4 Best solar energy conversion efficiencies for N719 DSSCs fabricated with time dependent dye loading.

Table 5 Best solar energy conversion efficiencies for Ru(dcb)(bpy)2 DSSCs fabricated with time dependent dye loading.

Lee

30

Figure 17 shows the photocurrent-voltage curves and the respective dark currents of the

best cells dye loaded

with carbazole dye. A

dye sensitized solar

cell dye loaded for 1

hour with carbazole

dye had a short circuit

current density of 2.61

mA/cm2, an open

circuit voltage of 0.60

V, and a fill factor of

0.73. The power

conversion efficiency

achieved was 1.15%. The dark current for the carbazole dye sensitized solar cell dye loaded for 1

hour had a short circuit current of -4.08E-4 mA/cm2, an open circuit voltage of -0.09 V, and a fill

factor of 0.32. The power conversion efficiency achieved was 1.17E-5%. The carbazole dye

sensitized solar cell dye loaded for 1 hour had the lowest efficiency compared to the 3 hour, 5

hour, and overnight carbazole dye loaded solar cells. A dye sensitized solar cell dye loaded for 3

hours with carbazole dye had a short circuit current density of 4.59 mA/cm2, an open circuit voltage

of 0.61 V, and a fill factor of 0.72. The power conversion efficiency produced was 2.03%, and this

was the second highest efficiency produced by the carbazole dye. The dark current for the

carbazole dye sensitized solar cell dye loaded for 3 hour had a short circuit current of -3.43E-4

-1

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Cu

rren

t D

ensi

ty (

mA

/cm

2)

Voltage (V)

1 Hour Cell 3

1 Hour Cell 3

Dark Current

3 Hour Cell 1

3 Hour Cell 1

Dark Current

5 Hour Cell 1

5 Hour Cell 1

Dark Current

Overnight Cell 1

Overnight Cell 1

Dark Current

Figure 17 The photocurrent-voltage curves and the respective dark currents (DC) on

the DSSCs dye loaded with carbazole dye at four different time increments 1 hour, 3

hour, 5 hour, and overnight.

Lee

31

mA/cm2, an open circuit voltage of -0.08 V, and a fill factor of 0.41. The power conversion

efficiency achieved was 1.18E-5%. On the other hand, a dye sensitized solar cell dye loaded for 5

hours produced an efficiency of 2.65%, which happens to be the highest overall efficiency out of

all of the dyes. The dark current for the carbazole dye sensitized solar cell dye loaded for 5 hour

had a short circuit current of -3.70E-4 mA/cm2, an open circuit voltage of -0.048 V, and a fill factor

of 0.95. The power conversion efficiency achieved was 1.67E-5%. A dye sensitized solar cell dye

loaded for 24 hours with carbazole dye had a short circuit current density of 3.40 mA/cm2, an open

circuit voltage of 0.59 V, and a fill factor of 0.69. The power conversion efficiency achieved was

1.41%. The dark current for the carbazole dye sensitized solar cell dye loaded for 24 hours had a

short circuit current

of -3.80E-4 mA/cm2,

an open circuit

voltage of -0.08 V,

and a fill factor of

0.42. The power

conversion

efficiency achieved

was 1.32E-5%.

Figure 18

shows the

photocurrent-voltage

curves and the respective


the DSSCs dye loaded with JK2 dye at four different time increments 1 hour, 3 hours,

5 hours, and 24 hours.

-0.1

0.1

0.3

0.5

0.7

0.9

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Cu

rren

t D

ensi

ty (

mA

/cm

2)

Voltage (V)

1 Hour Cell 2

1 Hour Cell 2 DC

3 Hour Cell 2

3 Hour Cell 2 DC

5 Hour Cell 1

5 Hour Cell 1 DC

24 Hour Cell 1

24 Hours Cell 1

DC

Lee

32

dark currents of the best cells dye loaded with JK2 dye. A dye sensitized solar cell dye loaded for

1 hour with JK2 dye had a short circuit current density of 1.16 mA/cm2, an open circuit voltage of

0.53 V, and a fill factor of 0.65. The power conversion efficiency achieved was 0.05%. The dark

current for the JK2 sensitized solar cell dye loaded for 1 hour had a short circuit current of -3.92E-

4 mA/cm2, an open circuit voltage of -0.04 V, and a fill factor of 0.21. The power conversion

efficiency achieved was 3.73E-6%. A dye sensitized solar cell dye loaded for 3 hours with JK2

dye had a short circuit current density of 0.20 mA/cm2, an open circuit voltage of 0.50 V, and a

fill factor of 0.60. The power conversion efficiency achieved was 0.06%. The dark current for the

JK2 sensitized solar cell dye loaded for 3 hours had a short circuit current of -0.06 mA/cm2, an

open circuit voltage of -0.04 V, and a fill factor of 0.21. The power conversion efficiency achieved

was 3.73E-6%. A dye sensitized solar cell dye loaded for 5 hours with JK2 dye had a short circuit

current density of 5.83 mA/cm2, an open circuit voltage of 0.61 V, and a fill factor of 0.74. The

power conversion efficiency achieved was 2.65%. The dark current for the JK2 sensitized solar

cell dye loaded for 5 hours had a short circuit current of -3.7E-4 mA/cm2, an open circuit voltage

of -0.09 V, and a fill factor of 0.51. The power conversion efficiency achieved was 1.64E-5%. A

dye sensitized solar cell dye loaded for 24 hours with JK2 dye had a short circuit current density

of 0.59 mA/cm2, an open circuit voltage of 0.56 V, and a fill factor of 0.75. The power conversion

efficiency achieved was 0.25%, which was the overall best efficiency for the cells dye loaded with

JK2 dye. The dark current for the JK2 sensitized solar cell dye loaded for 24 hours had a short

circuit current of -3.8E-4 mA/cm2, an open circuit voltage of -0.08 V, and a fill factor of 0.43. The

power conversion efficiency achieved was 1.20E-5%.

Lee

33


best cells dye loaded with N719 dye. A dye sensitized solar cell dye loaded for 1 hour with N719

dye had a short

circuit current

density of 3.83

mA/cm2, an open

circuit voltage of

0.68 V, and a fill

factor of 0.65. The

power conversion

efficiency

achieved was

1.71%. The dark

current for the N719

sensitized solar cell dye loaded for 1 hour had a short circuit current of -3.8E-4 mA/cm2, an open

circuit voltage of -0.06 V, and a fill factor of 0.60. The power conversion efficiency achieved was

1.32E-5%. A dye sensitized solar cell dye loaded for 3 hours with N719 dye had a short circuit

current density of 4.41 mA/cm2, an open circuit voltage of 0.67 V, and a fill factor of 0.46. The

power conversion efficiency achieved was 1.36%. The dark current for the N719 sensitized solar

cell dye loaded for 3 hours had a short circuit current of -3.4E-4 mA/cm2, an open circuit voltage

of -0.08 V, and a fill factor of 0.39. The power conversion efficiency achieved was 1.06E-5%. A

dye sensitized solar cell dye loaded for 5 hours with N719 dye had a short circuit current density

-0.1

0.4

0.9

1.4

1.9

2.4

2.9

3.4

3.9

4.4

0 0.2 0.4 0.6 0.8

Cu

rren

t D

ensi

ty (

mA

/cm

2)

Voltage (V)

1 Hour Cell 2

1 Hour Cell 2 DC

3 Hour Cell 2

3 Hour Cell 2 DC

5 Hour Cell 1

5 Hour Cell 1 DC

24 Hour Cell 4

24 Hour Cell 4

DC


the DSSCs dye loaded with N719 dye at four different time increments 1 hour, 3 hours,

5 hours, and 24 hours.

Lee

34

of 4.57 mA/cm2, an open circuit voltage of 0.66 V, and a fill factor of 0.76. The power conversion

efficiency achieved was 2.32%, which was the overall best power conversion efficiency for the

N719 dye sensitized solar cells. The dark current for the N719 sensitized solar cell dye loaded for

5 hours had a short circuit current of -3.8E-4 mA/cm2, an open circuit voltage of -0.08 V, and a

fill factor of 0.45. The power conversion efficiency achieved was 1.36E-5%. A dye sensitized solar

cell dye loaded for 24 hours with N719 dye had a short circuit current density of 4.56 mA/cm2, an

open circuit voltage of 0.62 V, and a fill factor of 0.52. The power conversion efficiency achieved

was 1.47%. The dark current for the N719 sensitized solar cell dye loaded for 24 hours had a short

circuit current of -8.2E-3 mA/cm2, an open circuit voltage of -0.0024 V, and a fill factor of 0.38.

The power conversion

efficiency achieved was

-7.41E-6%.

Figure 20 shows

the photocurrent-

voltage curves and the

respective dark currents

of the best cells dye

loaded with Ru(bpy)2

dye. A dye sensitized

solar cell dye loaded for

1 hour with Ru(bpy)2 dye had a

short circuit current density of 1. 17 mA/cm2, an open circuit voltage of 0.57 V, and a fill factor of

-0.1

0.1

0.3

0.5

0.7

0.9

1.1

1.3

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Cu

rren

t D

ensi

ty (

mA

/cm

2)

Voltage (V)

1 Hour Cell 3

1 Hour Cell 3 DC

3 Hour Cell 2

3 Hour Cell 2 DC

5 Hour Cell 1

5 Hour Cell 1 DC

24 Hour Cell 2

24 Hour Cell 2

DC

Figure 20 The photocurrent-voltage curves and the respective dark currents (DC)

for the DSSCs with the dye loaded with Ru(dcb)(bpy)2 dye at four different time

increments 1 hour, 3 hours, 5 hours, and 24 hours.

Lee

35

0.78. The power conversion efficiency achieved was 0.52%. The dark current for the

Ru(dcb)(bpy)2 dye sensitized solar cell dye loaded for 1 hour had a short circuit current of -5.56E-

4 mA/cm2, an open circuit voltage of -0.07 V, and a fill factor of 0.30. The power conversion

efficiency achieved was 1.16E-5%. A dye sensitized solar cell dye loaded for 3 hours with

Ru(dcb)(bpy)2 dye had a short circuit current density of 0.47 mA/cm2, an open circuit voltage of

0.51 V, and a fill factor of 0.76. The power conversion efficiency achieved was 0.18%. The dark

current for the Ru(dcb)(bpy)2 dye sensitized solar cell dye loaded for 3 hours had a short circuit

current of -3.17E-4 mA/cm2, an open circuit voltage of -0.08 V, and a fill factor of 0.45. The power

conversion efficiency achieved was 1.18E-5%. A dye sensitized solar cell dye loaded for 5 hours

with Ru(dcb)(bpy)2 dye had a short circuit current density of 1.17 mA/cm2, an open circuit voltage

of 0.56 V, and a fill factor of 0.70. The power conversion efficiency achieved was 0.45%. The

dark current for the Ru(dcb)(bpy)2 dye sensitized solar cell dye loaded for 5 hours had a short

circuit current of -4.46E-4 mA/cm2, an open circuit voltage of -0.04 V, and a fill factor of 0.35.

The power conversion efficiency achieved was 6.52E-6%. A dye sensitized solar cell dye loaded

for 24 hours with Ru(dcb)(bpy)2 dye had a short circuit current density of 0.57 mA/cm2, an open

circuit voltage of 0.51 V, and a fill factor of 0.75. The power conversion efficiency achieved was

0.21%. The dark current for the Ru(dcb)(bpy)2 dye sensitized solar cell dye loaded for 24 hours

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36

had a short circuit current of -5.70E-4 mA/cm2, an open circuit voltage of -0.02 V, and a fill factor

of 0.15. The power conversion efficiency achieved was 2.56E-6%.


best cells dye loaded with Carbazole, JK2, N719, and Ru(dcb)(bpy)2 dye. The best performing dye

sensitized solar cell constructed with Carbazole dye was dye loaded for 5 hours. It had a short

circuit current density of

5.83 mA/cm2, an open

circuit voltage of 0.61

V, and a fill factor of

0.74. The power


achieved was 2.65%.

The dark current for the

Carbazole dye sensitized

solar cell dye loaded for

5 hours had a short

circuit current of -4.76E-2

mA/cm2, an open circuit

voltage of 0.95 V, and a fill factor of 0.30. The power conversion efficiency achieved was 1.67E-

5%.

The best performing dye sensitized solar cell dye loaded with JK2 dye for 1 hour. It had a

short circuit current density of 0.95 mA/cm2, an open circuit voltage of 0.57 V, and a fill factor of

-1

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

Cu

rren

t D

ensi

ty (

mA

/cm

2)

Voltage (V)

Carbazole 5 Hour 1

Carbazole 5 Hour

Cell 1 Dark Current

JK2 1 Hour Cell 3

JK2 1 Hour Cell 3

Dark Current

N719 5 Hour Cell 1

N719 5 Hour Cell 1

Dark Current

Ru(dcb)bpy 1 Hour

Cell 3

Ru(dcb)bpy 1 Hour

Cell 3 Dark Current

Figure 21 The photocurrent-voltage curves and the respective dark currents (DC) for

the DSSCs with the highest efficiencies dye loaded with Carbazole, JK2, N719, and

Ru(dcb)(bpy)2 dye at four different time increments 1 hour, 3 hours, 5 hours, and 24

hours.

Lee

37

0.73. The power conversion efficiency achieved was 0.39%. The dark current for the JK2 dye

sensitized solar cell dye loaded for 5 hours had a short circuit current of -7.72E-4 mA/cm2, an open

circuit voltage of -0.09 V, and a fill factor of 0.34. The power conversion efficiency achieved was

2.29E-5%.

The best performing dye sensitized solar cell constructed with N719 dye was dye loaded

for 5 hours. It had a short circuit current density of 4.57 mA/cm2, an open circuit voltage of 0.66

V, and a fill factor of 0.76. The power conversion efficiency achieved was 2.32%. The dark current

for the N719 dye sensitized solar cell dye loaded for 5 hours had a short circuit current of -7.78E-

2 mA/cm2, an open circuit voltage of 0.45 V, and a fill factor of 0.45. The power conversion

efficiency achieved was 1.36E-5%.

The best performing dye sensitized solar cell dye loaded with Ru(dcb)bpy dye for 1 hour

had a short circuit current density of 1.17 mA/cm2, an open circuit voltage of 0.57 V, and a fill

factor of 0.78. The power conversion efficiency achieved was 0.52%. The dark current for the

Ru(dcb)(bpy)2 dye sensitized solar cell dye loaded for 5 hours had a short circuit current of -4.76E-

2 mA/cm2, an open circuit voltage of 0.95 V, and a fill factor of 0.30. The power conversion

efficiency achieved was 1.67E-5%.

Overall, Carbazole produced the DSSC with the highest efficiency of 2.64%. However,

N719 produced the highest open circuit voltage of 0.66 V, and the highest fill factor was produced

by Ru(dcb)(bpy)2 which was 0.78.

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38

Electron Lifetime Data

Figure 22 shows

the charge lifetime for the

dye sensitized solar cells

with the highest short

circuit currents (Jsc) that

were dye loaded with

Carbazole dye. At a

potential of 0.4 V, the

DSSC dye loaded with

Carbazole for 1 hour had

an electron lifetime of 0.1 seconds.

At a potential of 0.4 V, the DSSC

dye loaded with Carbazole for 3

hours had an electron lifetime of 0.4 seconds. At a potential of 0.4 V, the DSSC dye loaded with

Carbazole for 5 hours had an electron lifetime of 0.3 seconds. At a potential of 0.4 V, the DSSC

dye loaded with Carbazole for 24 hours had an electron lifetime of 0.2 seconds.

Figure 22 Charge lifetime as a function of photovoltage decay plot for the

dye sensitized solar cells with the highest short circuit current (Jsc). The dye

sensitized solar cells were dye loaded with Carbazole dye in four different

time increments (1 hour, 3 hours, 5 hours, and 24 hours).

0.01

0.1

1

10

0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6

CH

AR

GE

LIF

ET

IME

(S

)

PHOTOVOLTAGE (V)

1 Hour Cell 3

3 Hour Cell 1

5 Hour Cell 1

24 Hour Cell 1

Lee

39

Figure 23 shows the

charge lifetime for the dye

sensitized solar cells with

the highest short circuit

currents (Jsc) that were dye

loaded with JK2 dye. At a


DSSC dye loaded with JK2

for 1 hour had an electron

lifetime of 0.13 seconds. At

a potential of 0.4 V, the

DSSC dye loaded with JK2 for 3

hours had an electron lifetime of

0.07 seconds. At a potential of 0.4 V, the DSSC dye loaded with JK2 for 5 hours h ad an electron

lifetime of 0.28 seconds. At a potential of 0.4 V, the DSSC dye loaded with JK2 for 24 hours had

an electron lifetime of 0.22 seconds.


dye sensitized solar cells with the highest short circuit current (Jsc). The

dye sensitized solar cells were dye loaded with JK2 dye in four different

time increments (1 hour, 3 hours, 5 hours, and 24 hours).

0.01

0.1

1

10

0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6

CH

AR

GE

LIF

ET

IME

(S

)

PHOTOVOLTAGE (V)

1 Hour Cell 2

3 Hour Cell 3

5 Hour Cell 1

24 Hour Cell 1

Lee

40

Figure 24 shows the

charge lifetime for the dye

sensitized solar cells with the

highest short circuit currents

(Jsc) that were dye loaded with

N719 dye. At a potential of

0.4 V, the DSSC dye loaded

with N719 for 1 hour had an

electron lifetime of 0.08

seconds. At a potential of 0.4

V, the DSSC dye loaded with

N719 for 3 hours had an electron

lifetime of 0.34 seconds. At a

potential of 0.4 V, the DSSC dye loaded with N719 for 5 hours had an electron lifetime of 0.51

seconds. At a potential of 0.4 V, the DSSC dye loaded with N719 for 24 hours had an electron

lifetime of 0.26 seconds.



sensitized solar cells were dye loaded with N719 dye in four different time

increments (1 hour, 3 hours, 5 hours, and 24 hours).

0.01

0.1

1

10

0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6

CH

AR

GE

LIF

ET

IME

(S

)

PHOTOVOLTAGE (V)

1 Hour Cell 1

3 Hour Cell 2

5 Hour Cell 1

24 Hour Cell 4

Lee

41

Figure 25 shows




circuit currents (Jsc) that

were dye loaded with

Ru(dcb)(bpy)2 dye. At a


DSSC dye loaded with

Ru(dcb)(bpy)2 for 1 hour

had an electron lifetime of

0.08 seconds. At a potential of 0.4

V, the DSSC dye loaded with

Ru(dcb)(bpy)2 for 3 hours had an electron lifetime of 0.04 seconds. At a potential of 0.4 V, the

DSSC dye loaded with Ru(dcb)(bpy)2 for 5 hours had an electron lifetime of 0.07 seconds. At a

potential of 0.4 V, the DSSC dye loaded with Ru(dcb)(bpy)2 for 24 hours had an electron lifetime

of 0.02 seconds.



sensitized solar cells were dye loaded with Ru(dcb)(bpy)2 dye in four

different time increments (1 hour, 3 hours, 5 hours, and 24 hours).

0.01

0.1

1

10

0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5

CH

AR

GE

LIF

ET

IME

(S

)

PHOTOVOLTAGE (V)

1 Hour Cell 3

3 Hour Cell 2

5 Hour Cell 1

24 Hour Cell 2

Lee

42

Figure 26 shows




circuit currents (Jsc) for

Carbazole, JK2, N719,

and Ru(dcb)(bpy)2. At a


DSSCs dye loaded with

JK2 and Ru(dcb)(bpy)2

had equal electron lifetimes of 0.2

seconds. However, as the trend

continues the electron lifetime of

Ru(dcb)(bpy)2 is slightly longer, but the trends are very similar. At a potential of 0.35 V, N719 has

the highest electron lifetime, 1.50 seconds. Carbazole is closely behind with an electron lifetime

of 0.83 seconds. Overall, the trends of the photovoltage decays of Carbazole and N719 are similar

with N719 having a slightly longer electron lifetime.

Figure 26 Charge lifetime as a function of photovoltage decay plot for the dye

sensitized solar cells with the highest short circuit current (Jsc) for each of the 4

respective dyes (Carbazole, JK2, N719, and Ru(dcb)(bpy)2). The dye sensitized

solar cells were dye loaded in four different time increments (1 hour, 3 hours, 5

hours, and 24 hours).

0.01

0.1

1

10

0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6

CH

AR

GE

LIF

ET

IME

(S

)

PHOTOVOLTAGE (V)

Carbazole 5 Hour Cell 1

JK2 1 Hour Cell 3

N719 5 Hour Cell 1

Ru(dcb)bpy 1 Hour Cell 3

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43

Incident Photon-to-Current Conversion Efficiency (IPCE) Data

Dye Wavelength (nm) Incident Photon-to-Current

Conversion Efficiency (IPCE) Ratio

Carbazole 470 nm 0.05

JK2 480 nm 0.06

N719 530 nm 0.47

Ru(dcb)(bpy)2 480 nm 0.29

Cell Type Wavelength

(nm)

Incident Photon-to-Current Conversion

Efficiency (IPCE) %

Carbazole Front Side 470 nm 43.3%

Carbazole Back Side 470 nm 2.3%

JK2 Front Side 480 nm 15.7%

JK2 Back Side 480 nm 1.0%

N719 Front Side 530 nm 51.7%

N719 Back Side 530 nm 24.3%

Ru(dcb)(bpy)2 Front Side 480 nm 8.0%

Ru(dcb)(bpy)2 Back Side 480 nm 2.3%

Table 6 Peak Incident Photon-to-Current Conversion Efficiencies for Carbazole, JK2, N719, and Ru(dcb)(bpy)2

DSSCs fabricated with time dependent dye loading for 5 hours.

Table 7 Ratio of backside to front side Incident Photon-to-Current Conversion Efficiency for Carbazole, JK2,

N719, and Ru(dcb)(bpy)2 DSSCs fabricated with time dependent dye loading for 5 hours.

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Figure 27

shows the peak

Incident Photon-to-

Current Conversion

Efficiencies (IPCE)

for dye sensitized

solar cells dye loaded

with Carbazole, JK2,

N719, and Ru(bpy).

Backside and front

side illumination

incident photon-to

current conversion efficiencies

(IPCEs) are displayed. For Carbazole DSSCs, the peak incident photon-to-current efficiency

(IPCEmax) is 43.3% at 470 nm for front side illumination. For Carbazole DSSCs, the peak

incident photon-to-current efficiency (IPCEmax) is 2.3% at 470 nm for back side illumination. For

JK2 DSSCs, the peak incident photon-to-current efficiency (IPCEmax) is 15.7% at 480 nm for

front side illumination. For JK DSSCs, the peak incident photon-to-current efficiency (IPCEmax)

is 1.0% at 480 nm for back side illumination. For N719 DSSCs, the peak incident photon-to-

current efficiency (IPCEmax) is 51.7% at 530 nm for front side illumination. For N719 DSSCs,

the peak incident photon-to-current efficiency (IPCEmax) is 24.3% at 530 nm for back side

illumination. For Ru(dcb)bpy DSSCs, the peak incident photon-to-current efficiency (IPCEmax)

Figure 27 Spectra of incident photon-to-current conversion efficiencies

(IPCEs) for dye sensitized solar cells (DSSCs) based on Carbazole, JK2,

N719, Ru(dcb)(bpy)2 dye. The DSSCs were dye loaded for 5 hours.

0

10

20

30

40

50

4 0 0 4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0 8 0 0

IPC

E (

%)

WAVELENGTH (NM)

Carbazole Front Side

Carbazole Back Side

Ru(bpy) Front Side

Ru(bpy) Back Side

N719 Front Side

N719 Back Side

JK2 Front Side

JK2 Back Side

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is 8.0% at 480 nm for front side illumination. For Ru(dcb)(bpy)2 DSSCs, the peak incident

photon-to-current efficiency (IPCEmax) is 2.3% at 480 nm for back side illumination.

Figure 28

demonstrates the ratio of

incident photon-to-current


(IPCE) back side to front

side illumination for each

of the four dyes. The ratio

of back side to front side

IPCE for dye sensitized

solar cells (DSSCs) dye

loaded with Carbazole is 0.05 at

470 nm. The ratio of back side to

front side IPCE for dye sensitized

solar cells (DSSCs) dye loaded with JK2 is 0.06 at 480 nm. The ratio of back side to front side

IPCE for dye sensitized solar cells (DSSCs) dye loaded with N719 is 0.47 at 530 nm. The ratio of

back side to front side IPCE for dye sensitized solar cells (DSSCs) dye loaded with Ru(dcb)(bpy)2

is 0.29 at 480 nm.

Figure 28 Ratio of incident photon-to-current conversion efficiencies

(IPCEs), back side and front side illumination, for dye sensitized solar cells

(DSSCs) based on Carbazole, JK2, N719, Ru(dcb)(bpy)2 dye. The DSSCs

were dye loaded for 5 hours.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Carbazole JK2 N719 Ru(dcb)(bpy)2

IPC

E R

ati

o

Dyes

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Discussion and Analysis

Hypothesis I:

Solar conversion efficiency data indicated that the dyes with higher efficiencies (N719 and

JK2) had the highest efficiencies when dye loaded for 5 hours however, the dyes with lower

efficiencies achieved their highest efficiencies when dye loaded for one hour. The highest

efficiency produced from a dye sensitized solar cell dye loaded with Carbazole dye produced an

efficiency of 2.64%, and was dye loaded for 5 hours. The highest efficiency produced from a dye

sensitized solar cell dye loaded with JK2 produced an efficiency of 0.40%, and was dye loaded for

1 hour. The highest efficiency produced from a dye sensitized solar cell dye loaded with N719

produced an efficiency of 2.32%, and was dye loaded for 5 hours. The highest efficiency produced

from a dye sensitized solar cell dye loaded with Ru(dcb)(bpy)2 produced an efficiency of 0.52%,

and was dye loaded for 1 hour. From the solar conversion efficiency data, we can conclude that as

dye loading time progresses solar conversion efficiency increases. For dye sensitized solar cells

dye loaded with JK2 and Ru(dcb)(bpy)2, although the solar cells with the highest efficiencies were

dye loaded for 1 hour, the other cells dye loaded for longer produced efficiencies merely decimal

points away and so we can conclude that it is merely coincidental that this occurred.

Electron lifetime data was used to confirm that as dye loading time increases solar

conversion efficiency increases. Analyses of photovoltage decay plots indicated that electrons had

longer lifetimes as dye loading times increased. For dye sensitized solar cells dye loaded with

Carbazole, JK2, and N719 the solar cells with the shortest electron lifetime were all dye loaded for

1 hour. For dye sensitized solar cells dye loaded with Ru(dcb)(bpy)2, the solar cell shortest electron

lifetime was dye loaded for 24 hours, however since the decays from the dye sensitized solar cells

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dye loaded with Ru(dcb)(bpy)2, in general, were not that great we can conclude that this was

coincidental, and due to poor dye sensitized solar cell construction. In addition, the next dye

sensitized solar cell (DSSC) that was dye loaded with Ru(dcb)(bpy)2 with the shortest electron

lifetime was dye loaded for 1 hour. For dye sensitized solar cells dye loaded with Carbazole and

JK2 dye, the longest electron lifetime was found in dye sensitized solar cells dye loaded overnight

followed by the cells dye loaded for 5 hours. For dye sensitized solar cells dye loaded with N719

dye, the longest electron lifetime was found in dye sensitized solar cells dye loaded for 5 hours

followed by the cells dye loaded for 3 hours.

Hypothesis II:

Data gathered using UV-vis spectrometry indicated that Carbazole had the highest

extinction coefficient of 44,817 M-1cm-1, followed by JK2 (27,380 M-1cm-1), N719 (14,007 M1cm-

1), and Ru(dcb)bpy2 (12,142 M-1cm-1). In theory, those dyes with the largest extinction coefficient

have the best ability to absorb light. Despite having one of the lowest extinction coefficients, N719

had the largest spectra range from 400 nm to 750 nm. While Carbazole had an absorption spectra

range from 400 nm to 650 nm. JK2 had the shortest absorption spectra from 400 nm to 600 nm.

Ru(dcb)(bpy)2 had an absorption spectra range from 400 nm to 620 nm. As large spectra range

indicates more colors of light will be absorbed and since the cells were exposed to white light,

absorbing more colors in the spectrum lead to a larger efficiency.

Solar conversion efficiency data indicated that the dye sensitized solar cell that produced

the highest efficiency out of all solar cells tested was dye loaded with Carbazole dye for 5 hours.

The solar conversion efficiency produced was 2.64%. The dye sensitized solar cell with the second

highest efficiency was dye loaded with N719. The solar conversion efficiency achieved was

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2.32%. None of the dye sensitized solar cells dye loaded with JK2 for any of the dye loading times

had a solar conversion efficiency higher than N719 even though, JK2 has an extinction coefficient

that is almost double that of N719. In fact, dye sensitized solar cells dye loaded with JK2 had about

the same solar conversions efficiencies as Ru(dcb)(bpy)2 even though, Ru(dcb)(bpy)2 had the

smallest extinction coefficients out of all the dyes.

Hypothesis III:

Incident Photon-to-Current Efficiency (IPCE) data indicated that Ruthenium dyes have a

better ability at transporting electrons through the TiO2 conduction band than organic dyes. The

highest recorded front side Incident Photon-to-Current Conversion Efficiency (IPCE) out of all the

dyes was 51.7% at 530 nm, and was produced from a dye sensitized solar cell dye loaded with

N719 dye for 5 hours. The second highest front side Incident Photon-to-Current Conversion

Efficiency (IPCE) was 43.3% at 470 nm, and was followed by JK2 with a front side Incident

Photon-to-Current Conversion Efficiency (IPCE) of 15.7% at 480 nm, and Ru(dcb)(bpy)2 with a

front side Incident Photon-to-Current Conversion Efficiency (IPCE) of 8.0% at 480 nm. Although,

Carbazole had a high front side Incident Photon-to-Current Conversion Efficiency (IPCE)

percentage the back side Incident Photon-to-Current Conversion Efficiency (IPCE) percentage

was the second lowest recorded out of all the dyes and so the ratio of back side to front side Incident

Photon-to-Current Conversion Efficiency (IPCE) for dye sensitized solar cells dye loaded with

Carbazole was the lowest of all the 4 dyes. The Incident Photon-to-Current Conversion Efficiency

(IPCE) ratio for a dye sensitized solar cell dye loaded with Carbazole for 5 hours was 0.05. The

dye sensitized solar cell dye loaded with JK2 had the second lowest Incident Photon-to-Current

Conversion Efficiency (IPCE) ratio of 0.06. This indicates that organic dyes are not very good at

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electron collection through the TiO2 conduction band, and that a majority of the electrons are being

lost to interception in the back side Incident Photon-to-Current Conversion Efficiency (IPCE). On

the other hand, the Ruthenium dyes had the two highest Incident Photon-to-Current Conversion

Efficiency (IPCE) ratios of back side to front side illumination. The Incident Photon-to-Current

Conversion Efficiency (IPCE) ratio for a dye sensitized solar cell dye loaded with N719 for 5 hours

was 0.47. The Incident Photon-to-Current Conversion Efficiency (IPCE) ratio for a dye sensitized

solar cell dye loaded with Ru(dcb)(bpy)2 for 5 hours was 0.29. This evidence suggests that

Ruthenium dyes are better at electron collection from the TiO2 conduction band than organic dyes,

and do not loose many electrons to interception on back side illumination.

Electron lifetime data indicated that when comparing dyes of similar efficiencies the

electron lifetime was longer in Ruthenium dyes. N719 and Carbazole had similar efficiencies for

all times, however, N719 demonstrated a longer electron lifetime. JK2 and Ru(dcb)(bpy)2 had

similar efficiencies and Ru(dcb)(bpy)2 demonstrated a longer electron lifetime. This suggests that

Ruthenium dyes are able to collect more electrons in the TiO2 conduction band and transfer those

to current than organic dyes.

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Experimental Error

Human error may have occurred during construction of dye sensitized solar cells, however,

large trial size accounted for errors made during solar cell construction, and the experimenter

constructing the dye sensitized solar cells was kept constant throughout the experiment. An

estimated total of one third of the dye sensitized solar cells were shorted throughout this

experiment, and data was not collected for shorted solar cells. Dye sensitized solar cells can short

due to a number of causes such as improper sealing of the cell, improper attachment of

nanoparticles, pinholes caused by electrolyte, improper attachment of fluorine doped tin oxide

(FTO), excess of epoxy paste, etc. All shorted cells were reconstructed and retested to ensure

accurate results. During the time when data was being collected at Northwestern University, there

were problems with the Atomic Layer Deposition (ALD) which caused incomplete deposition of

TiO2 blocking layer on fluorine doped tin oxide (FTO) glass for the dye sensitized solar cells

(DSSCs). This error in the Atomic Layer Deposition (ALD) caused pinholes in some dye sensitized

solar cells. Also, the lamp used to test the solar cells was getting old and suffering from some

power fluctuations which caused some of the J-V curves to become a bit noisy. Towards the end

of experimentation, the dyes were beginning to become a bit old and that led to the cause of lower

efficiencies in retesting, but the general results still affirm the conclusion. All variables were held

constant throughout the course of experimentation and proper laboratory skills were used to

conduct research. Data contamination was avoided by wearing gloves and by washing all

equipment used in between procedural steps.

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Conclusion

The overall purpose of this experiment was to explore the mechanisms at work in dye

sensitized solar cells in order to construct the most efficient solar cell. The first hypothesis

predicted that there would be a direct relationship between dye loading times of nanoparticles

and solar conversion efficiency. Meanwhile, the second hypothesis predicted that an extinction

coefficient of a dye would not be the sole factor affecting solar conversion efficiency. The third

hypothesis indicated that the difference in dye structure between Ruthenium and organic dyes

would dictate the abilities of electrons through the beneficial and parasitic kinetic processes in a

dye sensitized solar cell.

Over 60 dye sensitized solar cells were constructed throughout the course of this

experiment. The dye sensitized solar cells were dye loaded with 4 dyes (Carbazole, JK2, N719,

and Ru(dcb)(bpy)2) for 4 different time periods (1 hour, 3 hours, 5 hours, and overnight). UV-vis

spectrometry was used to determine the extinction coefficients of the dyes, which determines

which dyes have the best ability to absorb light. A potentiostat was used to obtain J-V curves,

electron lifetimes, and Incident Photon-to-Current Conversion Efficiencies (IPCEs). J-V curves

were used to generate solar conversion efficiency. Electron lifetime plots were used to determine

how many electrons were collected across the TiO2 conduction band and converted to current.

Incident Photon-to-Current Conversion Efficiency (IPCE) data was used to determine how many

photons of light were being collected per electron.

In summary, hypothesis II and III were proven true, and hypothesis I must be revised.

As dye loading time increased so did solar conversion efficiency for cells dye loaded with

Carbazole and N719, however, the dye sensitized solar cells dye loaded with Carbazole and

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N719 for 5 hours often had greater solar conversion efficiencies than those dye loaded overnight,

and so for future experimentation one should look into dye loading times between 5 hours, but

less than 24 hours. Ru(dcb)(bpy)2 and JK2 demonstrated the highest efficiencies dye loaded after

1 hour, however, the electron lifetimes were longest as dye loading time increased. This indicates

that not much of the electrons are being transferred to current when being dye loaded for short

amounts of time. Extinction coefficients were found not to be the sole factor affecting solar

conversion efficiency as N719 outperformed JK2, although JK2 had a far higher extinction

coefficient. The data gathered from this experiment suggested that Ruthenium dyes are far better

at electron collection and loose less electrons to interception than organic dyes. The outcomes of

this investigation can look into improving the ability of organic dyes to handle the parasitic and

beneficial kinematic processes in dye sensitized solar cells. The implications of this experiment

can give insight in the processes that need to be improved in order to move dye sensitized solar

cell technology forward to compete with other alternative energy sources and fossil fuels.

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Appendix

Solar Conversion Efficiency for All DSSCs Carbazole Dye Sensitized Solar Cells

Cell Type Jsc (mA/cm2) Voc (V) Fill

Factor

Efficiency (%)

1 Hour Cell 1 0.847579 0.575039 0.598 0.291337


1 Hour Cell 2 0.822094 0.541278 0.637 2.84E-01

1 Hour Cell 2 Dark Current -0.0005832 -0.00252 -0.51121 -7.50E-07

1 Hour Cell 3 2.6072136 0.6024743 0.73346187 1.15210663


3 Hour Cell 1 4.59148 0.609715 0.724502 2.028238


3 Hour Cell 2 3.618585 0.624582 0.577 1.30371


5 Hour Cell 1 5.832836 0.614849 0.737735 2.645748


5 Hour Cell 2 3.253983 0.590068 0.589 1.130267


5 Hour Cell 3 0.858498 0.556953 0.722 0.345377


5 Hour Cell 4 1.51507 0.575635 0.745 0.649552


5 Hour Cell 5 2.480678 0.586249 0.78 1.133912


5 Hour Cell 6 2.156789 0.583468 0.346956 0.436616


24 Hour Cell 1 3.403884 0.593627 0.696532 1.407438


24 Hour Cell 2 3.377783 0.61066 0.682 1.40695


24 Hour Cell 3 3.154673 0.598284 0.724 1.365889


24 Hour Cell 4 3.055013 0.598128 0.661 1.206954


JK2 Dye Sensitized Solar Cells

1 Hour Cell 1 0.158874 0.530385 0.648 0.054609


1 Hour Cell 2 0.9503404 0.5708585 0.72980967 0.395928969


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Solar Conversion Efficiency for All DSSCs

JK2 Dye Sensitized Solar Cells

Cell Type Jsc

(mA/cm2)

Voc (V) Fill

Factor

Efficiency

(%) 1 Hour Cell 3 0.572 0.546 0.638 0.199


3 Hour Cell 1 0.104 0.505 0.416 0.022


3 Hour Cell 2 0.201 0.499 0.598 0.060


3 Hour Cell 3 0.764 0.547 0.764 0.320


5 Hour Cell 1 0.542 0.596 0.590 0.190


5 Hour Cell 2 0.398 0.567 0.590 0.133


Overnight Hour Cell 1 0.586 0.561 0.751 0.247

Overnight Hour Cell 1 Dark Current -0.0004 -0.075 0.425 1.20E-05


Overnight Cell 2 Dark Current -0.002 -0.003 -0.67 -2.60E-06

N719 Dye Sensitized Solar Cells

1 Hour Cell 1 4.315 0.65 0.554 1.555


1 Hour Cell 2 3.833 0.683 0.653 1.710


3 Hour Cell 1 Lighter 1.867 0.665 0.611 0.758


3 Hour Cell 2 Darker 4.409 0.667 0.461 1.357


5 Hour Cell 1 4.574 0.664 0.764 2.322



Overnight Hour Cell 1 Dark Current -0.0082 -0.0024 -0.375 -7.41E-06







Ru(dcb)(bpy)2 Dye Sensitized Solar Cells

1 Hour Cell 1 0.464 0.190 0.312 0.0275

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Solar Conversion Efficiency for All DSSCs

Ru(dcb)bpy Dye Sensitized Solar Cells

Cell Type Jsc

(mA/cm2)

Voc (V) Fill

Factor

Efficiency

(%) 1 Hour Cell 1 Dark Current 0.465585 0.19041 0.295322 0.026181

1 Hour Cell 2 0.484747 0.469352 0.368 0.083634


1 Hour Cell 3 1.1732648 0.5725148 0.78113173 0.524695139


3 Hour Cell 1 0.43258 0.511178 0.752 0.166332


3 Hour Cell 2 0.474506 0.510114 0.76 0.184047


5 Hour Cell 1 1.165124 0.555846 0.698 0.452185


5 Hour Cell 2 0.920766 0.076007 4.285798 0.299939



Overnight Hour Cell 1 Dark

Current

-0.00037 -0.04824 0.131059 2.37E-06



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