摘要
As the most prevalently used fullerene-based electron acceptor in organic-inorganic solar cells, [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) was isolated into three typical isomers of α-, β 1 - and β 2 -PC 71 BM with comparable molecular orbital energy levels for exemplifying a formulation engineering based on blending the three isomers to improve photovoltaic performance. The power conversion efficiency (PCE), photocurrent hysteresis and stability of planar heterojunction perovskite (CH 3 NH 3 PbI 3 ) solar cells have been optimized by formulation engineering with mixed PC 71 BM (α:β 1 :β 2 = 17:1:2), the specific mixture which represents the best electron acceptor superior to either each of the purified isomers or any other ternary isomers of PC 71 BM. Microscopic analyses support that molecular aggregation of the isomeric PC 71 BM was critical to influence the surface morphology and, in turn, the PCE in the range of 0.38-17.56% of the perovskite solar cells involved. This finding about isomer-dependent photovoltaic performance launches a heretofore unknown strategy of formulation engineering for making efficient electron acceptors by mixing various fullerene derivatives having isomeric structures or beyond.