1. Tandem Organic Photovoltaics Brian E. Lassiter

2. Organic Photovoltaics The promise of OPV Materials design Low-temperature processing Lightweight, low-cost materials Roll-to-roll fabrication 27/12/2012PARC Talk

3. Path to Commercialization 37/12/2012PARC Talk Efficiency Lifetime Low-cost fabrication

4. State of the Art 7/12/20124PARC Talk MaterialArchitectureAbsorption cutoff (nm) η p (%) V oc (V) FF (%) J sc (mA/cm 2 ) This groupDPSQ/C 60 Bilayer HJ8004.80.96727.2 Pandey et al.SubPc:C 60 Graded HJ6304.21.05498.2 Steinmann et al.Merocyanine:C 60 Bulk HJ6605.80.964712.6 Heeger groupDTS(PTTh 2 ) 2 :PCBMBulk HJ7606.70.785914.4 Yang groupPolymer:PCBMBulk HJ7.70.766715.2 Yang groupPolymer:FullereneTandem BHJ630, 8208.61.56678.3 IndustryUnknown >10

5. 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 7/12/2012PARC Talk

6. Literature 67/12/2012PARC Talk 5.2% 6.1%

7. Active Materials 77/12/2012PARC Talk DPSQ SubPc

8. Device Structure 87/12/2012PARC Talk Glass PTCBI Ag MoO 3 ITO DPSQ MoO 3 SubPc:C 70 Ag BCP C 70

9. Optical Modeling 97/12/2012PARC Talk MoO 3 DPSQC 70 PTCBI MoO 3 SubPc:C 70 C 70 BCP

10. Single-cell devices 107/12/2012PARC Talk Glass Ag MoO 3 5 nm ITO SubPc:C 70 29 nm BCP 7 nm C 70 3 nm Glass MoO 3 20.5 nm ITO 13.1 nm DPSQ PTCBI 5 nm C 70 10 nm Ag MoO 3 30 nm Ag 0.1 nm

11. Modeling Device Characteristics 117/12/2012PARC Talk

12. Optimization 127/12/2012PARC Talk Glass PTCBI 5 nm Ag MoO 3 20 nm ITO DPSQ 13 nm MoO 3 5 nm SubPc:C 70 Y nm Ag 0.1 nm BCP 7 nm C 70 3 nm C 70 X nm

13. Device Characteristics 137/12/2012PARC Talk Glass PTCBI 5 nm Ag MoO 3 20 nm ITO DPSQ 13 nm MoO 3 5 nm SubPc:C 70 29 nm Ag 0.1 nm BCP 7 nm C 70 3 nm C 70 10 nm

14. Quantum Efficiency 147/12/2012PARC Talk

15. Device Performance 157/12/2012PARC Talk DeviceIlluminationη p (%) V oc (V) FF (%) J sc (mA/cm 2 ) M Back-onlyExperiment4.3 ± 0.11.04488.51.04 Back sub-cellCalculation3.01.03496.01.03 Front-onlyExperiment4.1 ± 0.10.94716.10.94 Front sub-cellCalculation3.80.94715.70.90 TandemExperiment6.6 ± 0.11.97546.20.98 TandemCalculation6.61.97585.80.98

16. Summary Developed a model to predict tandem J-V characteristics Utilized solvent vapor annealing to increase DPSQ exciton diffusion length by ~100% Incorporated C 70, increasing J SC by >30% for each sub-cell Fabricated a tandem device with η P = 6.6% 167/12/2012PARC Talk

17. Acknowledgements 177/12/2012PARC Talk Optoelectronic Components and Materials Group Supported in part by AFOSR, DOE Sunshot Program, MKE Korea, and Global Photonic Energy Corp.

18. 187/12/2012PARC Talk

19. 197/12/2012PARC Talk

20. Solvent Annealing of DPSQ/C 60 cells DPSQ C 60 PTCBI MoO 3 ITO AgAg DPSQ 20 DeviceCrystallinityV OC J SC [mA cm -2 ] FFPCE As CastLeast0.96 V6.174%4.3% Pre C 60 Most0.84 V6.071%3.6% Post C 60 Middle0.97 V7.772%5.5% Improved bulk crystallinity  exciton diffusion (  J SC ) Crystalline interfaces  polaron recombination (  V OC ) Optimum bilayer device: Crystalline bulk and disordered D-A interface 7/12/2012PARC Talk