A tale of two organic small molecular hole transporting materials: Showing same extended shelf-life but very different efficiency of inverted MAPbI3 perovskite solar cells

Abstract

This paper mainly discusses the structure-property relationship of two donor-acceptor-donor (D–π–A–π–D) type dopant-free hole transporting materials (HTMs) ( TPA-TPy and TPA-Py-PTZ ) comprising primarily of 2,4,6-trisubstituted pyridine as the acceptor core and 4,4′-dimethoxytriphenylamine as the peripheral donor groups and their use in p-i-n perovskite solar cells (PVSCs). Compared to inferior TPA-Py-PTZ , TPA-TPy has a superior hole extraction and hole transport at the HTM/perovskite interface. The pinhole-free, smooth and dense, fully covered and well-crystallized MAPbI 3 perovskite layer on TPA-TPy reduces the carrier recombination and substantially improves the short circuit current density ( J SC ), open circuit voltage ( V OC ), and the fill-factor (FF) of MAPbI 3 PVSCs. The PVSC employing TPA-TPy as HTM exhibits a power conversion efficiency (PCE) of 15.33% with a J SC of 23.69 mA cm −2 , a V OC of 0.95 V, and a FF of 68.10%. Especially, both TPA-TPy and TPA-Py-PTZ PVSCs exhibit a better moisture stability than that of NiOx PVSCs. It is because of the hydrophobic nature of TPA-TPy and TPA-Py-PTZ , which enables the formation of MAPbI 3 perovskite layer having a larger grain-size, a less grain boundary, and a less infiltration of moisture. • Two organic small molecular hole transporting materials (HTMs) have been synthesized and characterized. • Compared to NiO x in the inverted MAPbI 3 perovskite solar cells, without using any p-type dopant, one of the two organic materials show comparable PCE 15–18% but the other is significantly worse PCE <7%. • Regardless the good or bad PCE, both organic HTMs provide an extended shelf-life for the perovskite solar cells, when compared with those devices based on NiO x . • It is the lab locked down (due to the COVID-19 pandemic) that unveiled the shelf-life difference of perovskite solar cells with organic or inorganic HTMs.