Non-radiative recombination at the interface of perovskite solar cells (PSCs) is a key issue limiting device efficiency and stability. The most advanced surface passivation strategies often utilize alkyl ammonium halides to suppress non-radiative recombination in PSCs, but their high surface reactivity leads to transformation into two-dimensional perovskites under operating conditions, limiting the passivation effect and charge transfer in PSCs.

Wei Zhanhua and Xie Liqiang et al. at Huaqiao University synthesized a non-halide ionic salt, 1-naphthylmethylammonium formate (NMACOOH), for surface passivation of perovskite thin films. Compared to traditional 1-naphthylmethylammonium iodide, NMACOOH treatment inhibited the formation of two-dimensional perovskites and formed thermally stable PbI2-NMACOOH adducts on the perovskite surface.

Surface characterization showed that NMA+ can passivate cation vacancies of 3D perovskites, while HCOO- can passivate metal Pb0 and halide vacancy defects. As a result, non-radiative recombination in PSCs was suppressed, yielding a high open-circuit voltage of 1.19 V. Ultimately, PSCs with efficiency as high as 24.75% and improved long-term stability (98% of initial efficiency after storage for 1800 hours) were obtained. In addition, the NMACOOH passivated devices also exhibited strong operational stability, retaining 83% of initial efficiency after working continuously under 1 sun for 658 hours.