Significant progress has been made in the field of organic photovoltaic (OPV) devices resulting in power conversion efficiencies (PCEs) over 10% in both polymer and small molecule based tandem devices. These improving PCEs can be primarily attributed to the development of new donor materials and advances in device engineering.In this talk, we demonstrate two families of novel low bandgap conjugated polymers (Eg ~ 1.4 eV) specifically suitable for tandem device architecture. One is based on alternating benzodithiophene/diketopyrrolopyrrole units and the other is based on alternating dithienopyran/diflourobenzothiadiazole units. In single-layer devices, power conversion efficiencies (PCE) of 7~8% were achieved. When the polymers were applied to tandem solar cells, we demonstrated a NREL certified record PCE of 10.6% (under the AM 1.5G solar condition). Furthermore, the tandem devices show excellent stability due both to the intrinsic stability of the polymer and the advanced device structure.In parallel with polymer donor materials, we recently developed a series of solution-processed small-molecule donors for high performance bulk heterojunction OPV cells. Conjugated acceptor-donor-acceptor small molecules using different electron linkers were designed, synthesized and fabricated into devices. A maximum PCE of 6.15% was achieved with T3, which uses selenophene as a linker. To further increase the performance of solution-processed small molecule solar cells, we recently designed and synthesized a two-dimensional conjugated small molecule (SMPV1). The single junction solar cells based on SMPV1 exhibited a certified power conversion efficiency of 8.02% under AM 1.5G irradiation (100 mW cm-2), making it the first certified small molecule solar cell with an efficiency over 8%. A homo-tandem solar cell based on SMPV1 was constructed with a novel interlayer (or tunnel junction) achieving PCE of over 10%.

Recent development of OPV materials and devices at UCLA

247th National Meeting (2014)

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