Metal halide perovskites are attractive candidates for the wide band gap absorber in tandem solar cells. While their band gap can be tuned by partial halide substitution, mixed halide perovskites often have lower open-circuit voltage than would be expected and experience photoinduced trap formation caused by halide segregation. We investigate solar cell performance and photostability across a compositional space of formamidinium (FA) and cesium (Cs) at the A-site at various halide compositions and show that using more Cs at the A-site rather than more Br at the X-site to raise band gap is more ideal as it improves both V_OC and photostability. We develop band gap maps and design criteria for the selection of perovskite compositions within the Cs_xFA_1–xPb(Br_yI_1–y)₃, space. With this, we identify perovskites with tandem-relevant band gaps of 1.68 and 1.75 eV that demonstrate high device efficiencies of 17.4 and 16.3%, respectively, and significantly improved photostability compared to that of the higher Br-containing compositions.

中文翻译：

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高效宽带隙钙钛矿的组成工程，对光致相分离具有改善的稳定性

金属卤化物钙钛矿是串联太阳能电池中宽带隙吸收体的诱人候选物。尽管可以通过部分卤化物取代来调节其带隙，但混合卤化物钙钛矿的开路电压通常比预期的低，并且会经历由卤化物偏析引起的光致陷阱形成。我们研究了在各种卤化物成分的A位置甲酰胺（FA）和铯（Cs）的组成空间上的太阳能电池性能和光稳定性，并表明在A位置使用更多的Cs而不是X位置使用更多的Br增加带隙更理想，因为它可以同时提高V _OC和光稳定性。我们为Cs _x FA _1–中的钙钛矿成分选择开发了带隙图和设计标准。_x Pb（Br _y I _{1 – y}） ₃，空间。由此，我们确定了与钙钛矿具有串联相关的带隙为1.68和1.75 eV的钙钛矿，它们分别显示出17.4％和16.3％的高器件效率，并且与较高含溴量的组合物相比，其光稳定性显着提高。