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

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(0.24)FA(0.76)PbI(3-x)Br(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(0.24)FA(0.76)PbI(3-x)Br(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 x 5 cm(2)) solar module exhibited a PCE of 13.92%, indicating the favorable uniformity of the Sr-doped Cs(0.24)FA(0.76)PbI(3-x)Br(x) film.