Tailorable PC71BM Isomers: Using the Most Prevalent Electron Acceptor to Obtain High-Performance Polymer Solar Cells

摘要

Despite being widely used as electron acceptor in polymer solar cells, commercially available PC71BM (phenyl-C-71-butyric acid methyl ester) usually has a "random" composition of mixed regioisomers or stereoisomers. Here PC71BM has been isolated into three typical isomers, alpha-, beta(1)-and beta(2)-PC71BM, to establish the isomer-dependent photovoltaic performance on changing the ternary composition of alpha-, beta(1)-and beta(2)- PC71BM. Mixing the isomers in a ratio of alpha/beta(1)/beta(2)= 8:1:1 resulted in the best power conversion efficiency (PCE) of 7.67% for the polymer solar cells with PTB7: PC71BM as photoactive layer (PTB7= poly[[4,8-bis[(2-ethylhexyl) oxy] benzo[1,2-b: 4,5b(')] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl]]). The three typical PC71BM isomers, even though sharing similar LUMO energy levels and light absorption, render starkly different photovoltaic performances with average-performing PCE of 1.28-7.44% due to diverse self-aggregation of individual or mixed PC71BM isomers in the otherwise same polymer solar cells.