Cyclization of methoxy groups on spiro-type hole transporting materials for efficient and stable perovskite solar cells

Hole transporting materials (HTMs) are vital in efficient and stable perovskite solar cells (PSCs). To improve the performance of PSCs, it is of great significance to design and optimize HTMs. Here, spiro-biOMe, an analogue of spiro-OMeTAD featuring one additional meta-methoxy group on each diarylamine moiety, is reported. The structure of this new HTM has been further elaborated to give another analogue, spiro-cyclOMe, where an alkyl chain links the two adjacent O atoms. The effect of chemical structure on molecular and photovoltaic properties has been studied. It was found that the hole mobility and thermal stability were noticeably increased in the case of spiro-cyclOMe. When used in the PSC device (used perovskite: Cs0.05FA0.95PbI3), spiro-cyclOMe delivers a power conversion efficiency (PCE) of over 23%, which is higher than spiro-biOMe (PCE = 20.19%) and spiro-OMeTAD (PCE = 22.61%). A device employing spiro-cyclOMe, with an active area of 0.56 cm2, exhibited a PCE of 21.64%. More importantly, PSCs employing spiro-cyclOMe as HTM also showed better stability than those employing spiro-OMeTAD.