Multifunctional organic ammonium dopants for electron transport layers in efficient inverted perovskite solar cells

Fullerenes are the most widely used electron transport material (ETM) in inverted perovskite solar cells (PSCs) with a p-i-n structure. However, nonradiative recombination at the interface between the perovskite and the ETM hinders the development of inverted PSCs. Herein, we introduce three nonvolatile ammonium salts, thiopheneethylammonium iodide (TEAI), phenethylammonium iodide (PEAI) and pyridinylmethylammonium iodide (PyAI), to dope into [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). Our findings reveal that the ammonium cations exhibit a nonuniform vertical distribution in PC61BM with accumulation at the interface, which simultaneously improves the interface modification and defect passivation of PC61BM. Compared to pristine PC61BM, the ammonium-doped PC61BM exhibits a smaller energy level offset with the perovskite, as well as higher electrical conductivity and electron mobility. Notably, TEAI-doped PC61BM possessed the highest electrical conductivity and electron mobility among the doped devices. As a result, devices utilizing ammonium-doped PC61BM exhibit better performance, achieving a champion power conversion efficiency (PCE) of 23.17% for the device with TEAI-doped PC61BM. This simple doping strategy opens up a new avenue for the suppression of nonradiative recombination in PSCs from multiple aspects.