The morphology and optoelectronic properties of wide-bandgap halide perovskites have profound influence on the performance of tandem solar cells in which these materials hold a great potential to push the efficiency beyond the maximum in single junction devices. Typically, alkali metals such as Cs⁺ are employed to overcome photo-instability in mixed-halide hybrid perovskites. However, while using the popular CsI in precursor solutions, small grain size (~250 nm) along with high densities of grain boundaries and their associated trap states are usually observed in polycrystalline films, leading to low photovoltaic performance. Here, we develop a non-stoichiometric one-step solution casting method to prepare wide-bandgap Cs_XMA_1-XPb(I_0·6Br_0.4)₃ films with reduced grain boundaries and high crystallinity using CsCl which plays a double role of Cs ⁺ source and crystallization controller. The resulting films exhibit improved carrier lifetime and mobility, and reduced carrier trap states. Elemental analysis revealed that some Cl ions remains in the final films, passivating the defect states. All these benefits led to high open circuit voltages and improved the power conversion efficiency (PCE) of Cs_0.1MA_0.9Pb(I_0·6Br_0.4)₃ perovskite solar cells from 13.20% to 15.16%. Moreover, the developed method is also found to enhance the hydrophobicity and moisture resistance of Cs_XMA_1-XPb(I_0·6Br_0.4)₃ films, which enabled the improvement in the device ambient stability.

宽带隙卤化物钙钛矿的形态和光电特性对串联太阳能电池的性能有着深远的影响，这些材料在单结器件中具有将效率推高至最大值的巨大潜力。通常，使用 Cs ⁺等碱金属来克服混合卤化物杂化钙钛矿中的光不稳定性。然而，在前驱体溶液中使用流行的 CsI 时，通常在多晶薄膜中观察到小晶粒尺寸（~250 nm）以及高密度的晶界及其相关的陷阱状态，导致光伏性能低下。在这里，我们开发了一种非化学计量的一步溶液铸造方法来制备宽带隙 Cs _X MA _1-X Pb(I _{0 ·6} Br _0.4 ) ₃薄膜具有减少的晶界和高结晶度，使用CsCl，它起到Cs  ⁺ 源和结晶控制器的双重作用。所得薄膜表现出改善的载流子寿命和迁移率，以及减少的载流子陷阱状态。元素分析表明，一些 Cl 离子保留在最终薄膜中，从而钝化了缺陷状态。所有这些好处导致了高开路电压并提高了 Cs _0.1 MA _0.9 Pb(I _{0 · 6} Br _0.4 ) _{3的功率转换效率 (PCE)}钙钛矿太阳能电池从 13.20% 提高到 15.16%。_{此外，还发现所开发的方法提高了Cs X} MA _1-X Pb(I _{0 · 6} Br _0.4 ) ₃薄膜的疏水性和耐湿性，从而提高了器件的环境稳定性。