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