Tandem Organic Photovoltaics
Brian E. Lassiter
Organic Photovoltaics
The promise of OPV• Materials design• Low-temperature processing• Lightweight, low-cost materials• Roll-to-roll fabrication
27/12/2012 PARC Talk
Path to Commercialization
37/12/2012 PARC Talk
• Efficiency• Lifetime• Low-cost fabrication
State of the Art
7/12/2012 4PARC Talk
Material Architecture Absorption cutoff (nm)
ηp
(%)Voc
(V)FF(%)
Jsc
(mA/cm2)
This group DPSQ/C60 Bilayer HJ 800 4.8 0.96 72 7.2
Pandey et al. SubPc:C60 Graded HJ 630 4.2 1.05 49 8.2
Steinmann et al. Merocyanine:C60 Bulk HJ 660 5.8 0.96 47 12.6
Heeger group DTS(PTTh2)2:PCBM Bulk HJ 760 6.7 0.78 59 14.4
Yang group Polymer:PCBM Bulk HJ 7.7 0.76 67 15.2
Yang group Polymer:Fullerene Tandem BHJ 630, 820 8.6 1.56 67 8.3
Industry Unknown Unknown >10
Tandem
5
Advantages• Increased absorption length• Decrease thermalization losses
Design requirements• Current must be matched in the subcells optical model
Front sub-cell
Interlayer
ITO
Metal
Back sub-cell
Glass
h
7/12/2012 PARC Talk
Literature
67/12/2012 PARC Talk
5.2% 6.1%
Active Materials
77/12/2012 PARC Talk
DPSQ
SubPc
Device Structure
87/12/2012 PARC Talk
Glass
PTCBI
Ag
MoO3
ITO
DPSQ
MoO3
SubPc:C70
Ag
BCPC70
C70
Optical Modeling
97/12/2012 PARC Talk
0.0
0.2
0.4
0.6
0.8
|E
|2
80 60 40 20 00
10
20
30
40
50
Qj
Distance from cathode (nm)
450 nm 550 nm 700 nm
MoO
3
DP
SQ
C70
PT
CB
I
MoO
3
Sub
Pc:
C70
C70
BC
P
Single-cell devices
107/12/2012 PARC Talk
Glass
Ag
MoO3 5 nmITO
SubPc:C70 29 nm
BCP 7 nm C70 3 nm
Glass
MoO3 20.5 nmITO
13.1 nm DPSQ
PTCBI 5 nm C70 10 nm
AgMoO3 30 nm
Ag 0.1 nm
Modeling Device Characteristics
117/12/2012 PARC Talk
Optimization
127/12/2012 PARC Talk
Glass
PTCBI 5 nm
Ag
MoO3 20 nm
ITO
DPSQ 13 nm
MoO3 5 nmSubPc:C70 Y nm
Ag 0.1 nm
BCP 7 nm C70 3 nm
C70 X nm
Device Characteristics
137/12/2012 PARC Talk
Glass
PTCBI 5 nm
Ag
MoO3 20 nm
ITO
DPSQ 13 nm
MoO3 5 nmSubPc:C70 29 nm
Ag 0.1 nm
BCP 7 nm C70 3 nm
C70 10 nm
Quantum Efficiency
147/12/2012 PARC Talk
Device Performance
157/12/2012 PARC Talk
Device Illumination ηp (%)
Voc
(V)FF (%)
Jsc (mA/cm2)
M
Back-only Experiment 4.3 ± 0.1 1.04 48 8.5 1.04
Back sub-cell Calculation 3.0 1.03 49 6.0 1.03
Front-only Experiment 4.1 ± 0.1 0.94 71 6.1 0.94
Front sub-cell Calculation 3.8 0.94 71 5.7 0.90
Tandem Experiment 6.6 ± 0.1 1.97 54 6.2 0.98
Tandem Calculation 6.6 1.97 58 5.8 0.98
Summary
• Developed a model to predict tandem J-V characteristics
• Utilized solvent vapor annealing to increase DPSQ exciton diffusion length by ~100%
• Incorporated C70, increasing JSC by >30% for each sub-cell
• Fabricated a tandem device with ηP = 6.6%
167/12/2012 PARC Talk
Acknowledgements
177/12/2012 PARC Talk
Optoelectronic Components and Materials Group
Supported in part by AFOSR, DOE Sunshot Program, MKE Korea, and Global Photonic Energy Corp.
187/12/2012 PARC Talk
197/12/2012 PARC Talk
Solvent Annealing of DPSQ/C60 cells
DPS
Q
C 60
PTCB
I
MoO
3
ITO
A g
DPSQ
20
Device Crystallinity VOC JSC [mA cm-2] FF PCE
As Cast Least 0.96 V 6.1 74% 4.3%
Pre C60 Most 0.84 V 6.0 71% 3.6%
Post C60 Middle 0.97 V 7.7 72% 5.5%
• Improved bulk crystallinity exciton diffusion ( JSC)
• Crystalline interfaces polaron recombination (VOC)• Optimum bilayer device:
Crystalline bulk and disordered D-A interface
7/12/2012 PARC Talk