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 27/12/2012PARC Talk

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

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 HJ Pandey et al.SubPc:C 60 Graded HJ Steinmann et al.Merocyanine:C 60 Bulk HJ Heeger groupDTS(PTTh 2 ) 2 :PCBMBulk HJ Yang groupPolymer:PCBMBulk HJ Yang groupPolymer:FullereneTandem BHJ630, IndustryUnknown >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 7/12/2012PARC Talk

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

Active Materials 77/12/2012PARC Talk DPSQ SubPc

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

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

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

Modeling Device Characteristics 117/12/2012PARC Talk

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

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 nm Ag 0.1 nm BCP 7 nm C 70 3 nm C nm

Quantum Efficiency 147/12/2012PARC Talk

Device Performance 157/12/2012PARC Talk DeviceIlluminationη p (%) V oc (V) FF (%) J sc (mA/cm 2 ) M Back-onlyExperiment4.3 ± Back sub-cellCalculation Front-onlyExperiment4.1 ± Front sub-cellCalculation TandemExperiment6.6 ± TandemCalculation

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

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.

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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