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.