A series of 4-octyloxybenzyl-adducted fullerene derivatives (PCBOEs) were employed as the electron collection materials (ECMs) in CH3NH3PbI3-based planar heterojunction perovskite solar cells. The PCBOE-based devices exhibited lower power conversion efficiency and larger hysteresis than the PCBM-based device owing to the low electron mobility of PCBOEs, which causes charge accumulation at the perovskite/ECM interface. Moreover, the photovoltage of the investigated devices is identical, which indicates that the band gap of CH3NH3PbI3 is predominant in determining the photovoltage in planar heterojunction PSCs.