High-efficiency ternary polymer solar cells employing the solid solution as the donor phase

The solid solutions comprising amorphous conjugated polymer PCDTBT and different fullerene derivatives, i.e. crystalline PC71BM and amorphous NC60BA, have been investigated. It is found that the solid solution based on NC60BA could produce more hole carriers at the room temperature due to a smaller activation energy from trap state to free carriers compared to that based on PC71BM. A higher hole carrier density could effectively fill traps and reduce the recombination loss during charge transport process. The solid solution based on PC71BM shows enhanced exciton dissociation probability at the solid solution/C60 heterojunction interfaces. With combining the advantages of both the solid solutions, a small amount of amorphous NC60BA was introduced into the PCDTBT:PC71BM bulk heterojunction structure and the ternary BHJ PSCs composed of PCDTBT, PC71BM and NC60BA were fabricated. The ternary PSCs display outstanding photovoltaic performance compared to the binary PCDTBT:PC71BM bulk heterojunction PSCs.