A dimeric fullerene derivative for efficient inverted planar perovskite solar cells with improved stability

Fullerene derivatives can efficiently passivate the interfacial defects of perovskite layers to improve the performance of perovskite solar cells. In this work, a new dimeric fullerene derivative (D-C-60) with two [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) units was designed, synthesized and applied as the electron transporting material (ETM) in perovskite solar cells (PSCs) taking advantage of its appropriate energy levels, relatively fast electron mobility, and easy solution processability compared to the widely used PC61BM, D-C-60 can efficiently passivate the trap states between the perovskite and fullerene layers, leading to improved electron extraction and overall photovoltaic performance. Devices based on D-C-60 as the ETM achieved power conversion efficiencies (PCEs) of 16.6%, which is significantly higher than that observed with PC61BM (14.7%). In addition, the more hydrophobic and compact D-C-60 layer resulted in higher device stability than that with PC61BM. These results show that covalently linked dimeric fullerene derivative can act as efficient electron transporting materials (ETMs) for high performance PSCs.