Improving the crystal growth of a Cs0.24FA0.76PbI3−xBrx perovskite in a vapor–solid reaction process using strontium iodide

Abstract

Preparing organic–inorganic hybrid perovskite films by deploying vacuum-based methods, which are widely used for industrial thin-film deposition, is expected to promote the commercialization of perovskite solar cells. In comparison with solution processes, vacuum-based deposition methods could provide some unique benefits for producing high-quality thin films, such as providing the ability to precisely determine the thickness of the film, producing a pinhole-free morphology, and high reproducibility. However, in the “two-step” method of preparing an organic–inorganic hybrid perovskite, the PbI₂ films deposited using thermal evaporation are too dense to react with the organic component, leaving residual PbI₂ in the perovskite. To address this issue, we developed a new doping strategy to help the crystal growth of Cs_0.24FA_0.76PbI_3−xBr_x perovskites in the vapor–solid reaction process. By introducing a moderate amount of SrI₂ into the PbI₂ layer, we successfully enhanced the reactivity of PbI₂ and improved the crystallinity of these perovskites. As a result, the perovskite solar cell based on such Sr-doped Cs_0.24FA_0.76PbI_3−xBr_x films achieved a champion power conversion efficiency (PCE) of 17.66%. The device, without being encapsulated, maintained 95% of its initial PCE in an air atmosphere after 60 days. Moreover, the champion large-area (5 × 5 cm²) solar module exhibited a PCE of 13.92%, indicating the favorable uniformity of the Sr-doped Cs_0.24FA_0.76PbI_3−xBr_x film.