Transition Metal-Oxide Free Perovskite Solar Cells Enabled by a New Organic Charge Transport Layer

Various electron and hole transport layers have been used to develop high-efficiency perovskite solar cells. To achieve low-temperature solution processing of perovskite solar cells, organic n-type materials are employed to replace the metal oxide electron transport layer (ETL). Although PCBM (phenyl-C61-butyric acid methyl ester) has been widely used for this application, its morphological instability in films (i.e., aggregation) is detrimental. Herein, we demonstrate the synthesis of a new fullerene derivative (isobenzofulvene–C60–epoxide, IBF–Ep) that serves as an electron transporting material for methylammonium mixed lead halide-based perovskite (CH3NH3PbI3–x Cl x ) solar cells, both in the normal and inverted device configurations. We demonstrate that IBF–Ep has superior morphological stability compared to the conventional acceptor, PCBM. IBF–Ep provides higher photovoltaic device performance as compared to PCBM (6.9% vs 2.5% in the normal and 9.0% vs 5.3% in the inverted device configuration). Moreover, IBF–Ep devices show superior tolerance to high humidity (90%) in air. By reaching power conversion efficiencies up to 9.0% for the inverted devices with IBF–Ep as the ETL, we demonstrate the potential of this new material as an alternative to metal oxides for perovskite solar cells processed in air.