Polymer solar cells with improved power conversion efficiency using solvent mixtures

In this paper, the effects of solvent mixtures on the morphology, charge transport, and light trapping of poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)](PCDTBT) and [6,6]- phenyl C71-butyric acid methyl ester(PC71BM) based solar cells were investigated. As a good solvent for PCDTBT, o-dichlorobenzene(ODCB) was selected to mix with chloroform(CF), chlorobenzene(CB), and 1,2,4-Trichlorobenzene(TCB) for optimizing the morphology of the PCDTBT:PC71BM active layer. It can be found that the device performance of polymer solar cells(PSCs) has been greatly improved when using a optimal blend ratio. Especially, the PSCs fabricated via ODCB(90%)/CF(10%, volume fraction) mixture exhibit a remarkable enhancement of photon-to-current efficiency(PCE) from 5.16% to 7.47%. The enhanced performance of the PSCs can be attributed to the higher absorption, the lower resistance, and the optimized surface morphology of the active layers modified by the solvent mixtures.