Enhanced Open Circuit Voltage and Efficiency of Donor-Acceptor Copolymer Solar Cells by Using Indene-C60 Bisadduct

The photovoltaic properties of bulk heterojunction solar cells using indene-C60 bisadduct (ICBA) as the electron acceptor were investigated by using three donor-acceptor copolymers (PSEHTT, PSOTT, and PSOxTT) in comparison with PC61BM-based solar cells. The open circuit voltage of the copolymer:ICBA devices was 0.82-0.92 V, which is 0.25 V enhanced compared to the copolymer:PCBM solar cells. Compared to PCBM-based solar cells, the photocurrent density of ICBA-based devices was significantly increased in the case of PSEHTT but decreased in PSOTT and PSOxTT. This variation of photocurrent density with the copolymer structure was correlated with the charge photogeneration efficiency as determined by transient absorption spectroscopy. A power conversion efficiency of 5.4% was achieved in PSEHTT:ICBA solar cells, which represents a 50% enhancement in efficiency compared to PC61BM devices. Our results demonstrate that ICBA can significantly increase the open circuit voltage, current density, and power conversion efficiency of donor acceptor copolymer-based BHJ solar cells.