Nathan Duderstadt, Chemical Engineering, University of CincinnatiStoney Sutton, Electrical Engineering, University of CincinnatiKate Yoshino, Engineering Physics, Taylor University

Advisors: Ms. Yan Jin and Dr. Vikram Kuppa1

CEAS REU Project 4Synthesis of Solar Cell Materials and Fabrication of Novel Polymer-Based Solar Cells

Grant ID No.: DUE-0756921

2

Introduction

Why solar cells?

Why ORGANIC solar cells?

What is graphene and what role does it play?

3

In a semiconductor, the energy from the sun both moves the electron to an excited state, but also creates a hole (positive charge) in its place.

Lowest UnoccupiedMolecular Orbital

Solar Radiatio

n

Charge Generation

Electric Current

Charge Transport

to Electrodes

-+Highest OccupiedMolecular Orbital

Animation and concepts adapted from Dr. Vikram Kuppa’s presentation on organic photovoltaics

Background Literature Review

4Picture from: Deibel, Carsten, and Vladimir Dyakonov. (2010). " Polymer–fullerene Bulk Heterojunction Solar Cells.." Vol. 73.9, pp. 1-39.

Problems with Semiconductors: Charge Separation Charge Transfer

Solutions: Bulk-

heterojunction structured active layer

Graphene

Organic Photovoltaic Devices

5

So, Why Graphene?

High aspect ratio Conductivity Enables lower concentration

of graphene

Charge transport Hole AND Electron

Drawbacks Increase charge recombination Difficult to control morphology

Atomic Force Microscopy Image of 0.045 mg/ml 300 mesh graphene solution

5 μm

6

ITO

+

-

Aluminum

Charge Transport Via Graphene

Animation adapted with permission from a presentation by Fei Yu

P3HTF8BTElectronHole

Graphene

7

Goals and Objectives

We aim to determine how graphene makes solar cells more efficient.

Learn the basics of Organic Photovoltaic (OPV) research

Gain expertise in making and characterizing OPV cells

Differentiate between processing techniques and their influence on the solar cell

Evaluate graphene content on cell performance

8

1. Learn methods for making graphene solutions and fabricating solar cell devices

2. Prepare and analyze graphene solutions for use in solar cell polymers

3. Fabricate solar cell devices and perform thermal treatment

4. Characterize the cell through various testing

5. Conduct morphology and conductivity studies on the polymer films with different graphene concentrations

6. Report writing and presentations

Tasks

9

Task1 2 3 4 5 6 7 8

Training: Make Graphene Solution, Fabricate Solar

Cell              

Conductivity Studies for Graphene

Variations                

Solar Cell Fabrication and Testing

               

Data Analysis               

Work on Deliverables: Paper, Presentation,

Poster                

Week

Timeline and Schedule

✓ ✓

✓ ✓

✓

✓

✓ ✓

✓

✓

✓

✓✓

✓

✓

✓✓

✓

10

Progress Report

Report and Presentation

Data Analysis

Conductivity Studies

Solar Cell Fabrication

Training

Literature Review

0 10 20 30 40 50 60 70 80 90 100

Percentage Complete[%]

11

Methods

Making Graphene Solutions

Blending P3HT and Graphene

Spin Coating Procedure

Electrode Deposition

12

Methods

Performance Testing Morphology

Testing

13

Cell Structure

Aluminum (Cathode)

Lithium Fluoride

Active Layer (P3HT:F8BT:Graphene)

PEDOT:PSS

Indium Tin Oxide (Anode)

Glass Slide

The thickness of the cell is approximately without the glass slide is approximately 500 nm in thickness.

14

Aluminum (Cathode)

Indium Tin Oxide (Anode)

Active layer

Glass Slide

Solar Cell

Cell Structure

15

Conductivity Testing

Parameters:

Graphene concentration

Application method

Electrode configuration

Graphite type

Sonication time

16

Graphene vs. Conductivity

0 0.025 0.05 0.10E+001E+062E+063E+064E+065E+066E+067E+068E+06

Mean Resistance vs Graphene Concentration, Not Short-Circuited Samples

Graphene Concentration (mg/mL)

Resi

stan

ce (O

hms)

17

Conductivity Summary

Increase in graphene leads to increase in conductivity

0.1 mg/ml had the highest conductivity, but has potential for short-circuiting

18

Solar Cell Efficiency

0 0.025 0.05 0.10.0E+00

2.0E-03

4.0E-03

6.0E-03

8.0E-03

1.0E-02

1.2E-02

1.4E-02

Mean and Maximum Efficiencies vs Graphene Concentration

Eff(all)Eff (max)

Graphene Concentration (mg/mL)

Perc

ent E

ffici

ency

19

Crystallization

400 450 500 550 600 650 700

UV Absorbtion vs Wavelength, Normalized by Peak

0 mg/mL Graphene

0.025 mg/mL Graphene

0.05 mg/mL Graphene

0.1 mg/mL Graphene

Wavelength (nm)

No

rma

lize

d A

bso

rpti

on

20

X-ray Diffraction

0 0.025 0.05 0.116.6516.7

16.7516.8

16.8516.9

16.9517

17.0517.1

17.15

Graphene Concentration vs. XRD Findings

Crystal Sized-spacing

Graphene Concentration (mg/mL)

Leng

th (A

ngst

rom

s)

21

Summary

Conductivity is improved with the use of graphene.

0.1 mg/ml graphene concentration allows for greatest amount charge transport and highest efficiency in cells.

More testing needs to be done for result confirmation.

22

References

Chen,Y., Liu,Q., Liu, Z., et al., (2009). "Polymer Photovoltaic Cells Based on Solution-Processable Graphene and P3HT." Advanced Functional Materials Journal, Vol. 19,No.6, pp. 894-904.

Deibel, C, and V. Dyakonov. (2010). "Polymer–fullerene Bulk Heterojunction Solar Cells," Reports on Progress in Physics, IOP, Vol. 73, No. 9, pp. 1-39.

Li,G., Yang,Y., and R. Zhu.(2012). "Polymer Solar Cells." NATURE PHOTONICS No.6, pp.153-161.

McNeill, C.R., et al. (2007). , “Influence of Nanoscale Phase Separation on the Charge Generation Dynamics and Photovoltaic Performance of Conjugated Polymer Blends: Balancing Charge Generation and Separation.” Journal of Physical Chemistry C, Vol. 111, No. 51, pp. 19153-19160.

23

References

Saricifti, N.S. (2001). “Plastic Solar Cells.” Abstracts of Papers of the American Chemical Society, Vol. 222, pp. U281-U281.

Shin, M., H. Kim, and Y. Kim. (2011). “Effect of film and device annealing in polymer:polymer solar cells with a LiF nanolayer.” Materials Science and Engineering B- Advanced Functional Solid-state Materials, Vol. 176, No. 5, pp. 382-386.

Wan, X., Guiankui L., Lu H., and Y.Chen. (2011), “Graphene- A Promising Material for Organic Photovoltaic Cells.” Advanced Materials, Vol. 23, pp. 5342-5358.

Yu, D., et al. (2010), “Soluble P3HT-Grafted Graphene for Efficient Bilayer- Heterojunction Photovoltaic Devices.” ACS Nano, Vol. 4, No. 10, pp. 5633-5640.

24

Questions?Thank you!

25

26

27

Short-circuiting

0 mg/ml 0.025 mg/ml 0.05 mg/ml 0.1 mg/ml0102030405060708090100

Number of Short-circuited Samples vs. Graphene Concentration

Percentage of Short-circuiting due to Percolation

Percentage of Total Number of Short-circuited samples

Graphene Concentration (mg/ml)

Perc

enta

ge