High-efficiency perovskite solar cells have been developed by the incorporation of various electron and hole transport layers. In particular, transition metal oxides have been widely used as the electron transporting materials, despite their demands for high-temperature sintering steps which are not compatible with perovskite materials which cannot tolerate heating above 100 oC. In order to achieve low-temperature solution processing of the perovskite solar cells, organic n-type materials are employed to replace the metal oxide electron transport layer (ETL). Herein, we demonstrate the synthesis of new fullerene derivative (isobenzofulvene–C60–epoxide, IBF–Ep) which can serve as the electron transporting material in the normal and the inverted configurations of the methylammonium mixed lead halide-based perovskite (CH3NH3PbI3−xClx) solar cells. The superior morphological stability of IBF–Ep over that of a conventional acceptor (phenyl-C61-butyric acid methyl ester, PCBM) was verified, which resulted in the higher photovoltaic performance of the devices with IBF–Ep ETLs (6.9%) compared to those with PCBM (2.5%) in the normal device structures. Moreover, the superior tolerance of IBF–Ep devices to high humidity (90%) under the ambient processing conditions was determined compared to the PCBM devices. The inverted device structures fabricated with IBF–Ep ETLs produced PCE of 9.0%, which demonstrates the high potential of this new material as an alternative component of metal oxides for perovskite solar cells and for other potential applications.