Enhanced hole transport in benzoic acid doped spiro-OMeTAD composite layer with intergrowing benzoate phase for perovskite solar cells

Spiro-OMeTAD is one of the widely used hole-transfer materials for designing high-performance perovskite solar cells . It is reported that acid doping is an efficient and facile method to increase the conductivity of spiro-OMeTAD and accelerate its oxidation process . Besides, investigating the morphologic controlling mechanism of spiro-OMeTAD films would give a novel insight in designing the hole-transport layer (HTL) and further clarify the mechanism of acid additives. In this work, the effect of benzoic acid on the spiro-OMeTAD oxidation is studied, where the formation of the lithium benzoate phase can decrease the size of hollows in the spiro-OMeTAD film. By doping benzoic acid, the HTL exhibits faster oxidation process and better hole transfer ability. Meanwhile, the hysteresis of the perovskite solar device based on the HTL is effectively reduced via optimizing the doping content, with an improved power conversion efficiency reaching up to 16.26% under standard AM 1.5G illumination.