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