Stereomeric effects of bisPC71BM on polymer solar cell performance

Two stereomers of bisadduct analogues of [6,6]-phenyl-C71-butyric acid methyl ester (bisPC71BM) were synthesized and their geometrical structures with cis- or trans-configuration were identified by X-ray crystallography. Although both of the bisPC71BM have similar spectrometric and electrochemical properties, the spatial orientation of the two addition groups on C70 has impact on crystal packing and molecular assembly of bisPC71BM isomers and, in turn, photovoltaic performance in polymer solar cell based on poly(3-hexylthiophene) (P3HT) (with power conversion efficiency of 1.72% and 1.84% for the solar cells involving cis- and trans-bisPC71BM, respectively). Although the power conversion efficiency remains to be improved, this work exemplifies that the photovoltaic properties of fullerene-based electron acceptors are influenced by aggregation of the stereomeric molecules and thus extends the guidelines for rational design of efficient fullerene acceptor.