π–π stacking small molecules enable high performance perovskite solar cells

Abstract

Organic–inorganic hybrid perovskite materials have become promising photovoltaic materials due to their excellent optoelectronic properties and low-cost processing techniques. Among them, formamidine-cesium (FA-Cs) lead perovskite has attracted widespread attention because of its ability to enhance the stability of perovskite solar cells. However, large formamidinium (FA) cations cause severe micro-strain in the perovskite film, leading to defects and non-radiative recombination, which significantly impair the efficiency and long-term stability of the devices. In this study, by introducing π-conjugated molecules, such as bromobenzoic acid (BAC) additives, into the perovskite precursor solution, the micro-strain in the film was effectively relieved. Combining their π-electron conjugation at the grain boundaries of the film, they enhanced the carrier transport on the surface of the perovskite, ultimately improving the device efficiency from 22.70% to 24.02%, while also further enhancing the stability of the device. This work provides an effective approach for designing high-performance FA-Cs-based perovskite devices and offers important references for the selection and design of π-conjugated molecules.