Raising the LUMO level of fullerene derivatives alleviates the output voltage loss in tin halide perovskite solar cells.

Two fullerene derivatives C 60 -MP and C 60 -ETPA were designed and synthesized for tin-halide perovskite solar cells. The introduction of an electron-withdrawing group and an alkyl chain reduced the electron affinity, resulting in a shallower lowest unoccupied molecular orbital (LUMO) energy level than that of common phenyl-C 61 -butyric acid methyl ester (PC 61 BM). Moreover, the smaller energy level offset provided efficient carrier transport and suppressed charge recombination. As a result, the devices with C 60 -ETPA achieved an open-circuit voltage of 0.76 V and a power conversion efficiency of over 10%, which were substantially higher than 0.63 V and 8.25% for the control devices with PC 61 BM, respectively.