Incidence Angle Dependence of Organic Solar Cells

1)Dept. of Physics, John Carroll University, University Heights OH 2) Dept. of Physics, Case Western Reserve University, Cleveland OH

Vincent DeGeorge1, Brent Valle2, Kenneth Singer PhD. 2

Introduction and Background

M. A. Green, Third generation photovoltaics. Springer (2003).

•1st Generation: Bulk Silicon/semiconductor substrates•2nd Generation: Thin film compound semiconductors•3rd Generation: Organic Polymer materials

Organic Photovoltaics

1. Photon absorption, creation of exciton2. Exciton Diffusion3. Electron/Hole separation at interface4. Charge transport along polymer chain5. Charge collection at electrodes

n/donor p/acceptor

LUMO

HOMO

EF

PCBMP3HT

Electrode

Electrode

Al

ITO

P.V.

Incide

nt

Refle

cte

d 102

nm

Device Structure

Certain material thicknesses produce optical cavity resonance

1inch

• The incident angle of the sun varies throughout the day and season

• How is the performance of the cell effected by non-normal incidence? Optical cavity resonance?

Motivation

Solar Panel

12:00 pm

4:00 pm

90°30°

11 121 1 2 2 3 3 4

21 22

S SS I L I L I L I

S S

amb sub

amb sub

E ES

E E

21

11

Reflection, amb

amb

E SR

E S

TheoryInt1 Int2

layer1 layer2

Int3 Int4

Ambient Substratelayer3

d2

n1

k1

φ 3E

3E

Layer/Phase Matrix, L, and Interface Matrix, I, depend on: Refraction index, n Absorption index, k Incidence Angle, φ Thickness, d

Computation

θ

Detector

Light Source

Aperture

FocusingLens

FocusingLens

Sample

Rotary Stage

Experimental Setup

•CARY Spectrophotometer used to measure normal reflectance

•Ocean Optics light source and spectrophotometer supplied and detected light to and from the sample respectively

•Reflection data recorded as a ratio to a mirrored, 100% reflection, measurement

Results and Analysis

300 400 500 600 700 800 9000

0.2

0.4

0.6

0.8

1Bragg Interference

Wavelength [nm]

Re

flect

ion

(Ra

tio t

o T

ota

l)

inc

=0o

inc

=40o

inc

=70o

300 400 500 600 700 800 9000

20

40

60

80

100ITO(110nm), PV(200nm)

Wavelength(nm)

Re

flect

ion

inc

=0o

inc

=40o

inc

=70o

300 400 500 600 700 800 900

0

20

40

60

80

100ITO(110nm), PV(200nm)

wavelengths(nm)

Per

cent

Ref

lect

ion

inc

= 20o

inc

= 37.5o

inc

= 43.5o

Results and Analysis(cont)

300 400 500 600 700 800 900

0

0.2

0.4

0.6

0.8

1ITO(110nm), PV(150nm)

Wavelength(nm)

Ref

lect

ion

(Rat

io)

ExperiementSimulation

ITO(110nm), PV(150nm)

Reflect

ion

(Rati

o)

Wavelength(nm) Incidence Angle(degrees)

20

300 400 500 600 700 800 900

0

20

40

60

80

100

inc

=40.5o

Re

fle

cti

on

(

ra

tio

)

Above Left: Features characteristic to the experimental reflection curves are identified and translated onto the simulated reflection curves at the same wavelength

Above Right: A simulated contour plot is produced for a given sample at all angles of incidence, 0<θinc <90

Right: Comparison of features from experimental reflection data to Matlab simulation show considerable agreement in waveform and shift with incidence angle

θinc =20°

• Simulation was generalized for any incident angle

• Experimentally determined reflection spectrums were confirmed by generalized simulation

• Most features remain largely unshifted through incident angle changes

• Absorption peak sees largest shift, as large as 40nm

Conclusions and Acknowldgments

We acknowledge funding from the National Science Foundation CWRU Physics Department REU program under grant number: DMR-0850037,and the Center for Layered Polymer Systems under grant number: 0423914