Invert perovskite solar cells (PSCs) present a great potential for next-generation photovoltaics for their flexibility and tandem adaptability. In order to improve the conductivity of the hole transport layer (HTL), such as poly(triarylamine), highly conductive additives (e.g., F4TCNQ, Li-TFSI) were generally applied to achieve a power conversion efficiency (PCE) exceeding 21%. However, these additives significantly affect the long-term stability of the devices due to their humidity sensitivity. In this work, the HTL was counterintuitively optimized with insulating additives, such as polyphenylene sulfide, which enhanced PCE from 19.1 to 21.5% along with a noticeable improvement in device stability with T50 of 574 h under double 85 aging conditions. The performance enhancement is attributed to larger grain sizes in perovskite films on the HTL and better energy-level alignment between the HTL and perovskite after introducing the insulating additives, which compensate negative influence caused by additive-induced reduction in conductivity. Our work demonstrates that low-conductivity additives, rather than the commonly used high-conductivity counterparts, can also contribute to improving the photovoltaic performance in PSCs.
Keywords: additives; conductivity; hole transport layer (HTL); inverted PSC; perovskite solar cell (PSC).