The emerging inorganic CsPbI₃ perovskites are promising wide‐bandgap materials for application in tandem solar cells, but they tend to transit from a black α phase to a yellow δ phase in ambient conditions. Herein, a gradient grain‐sized (GGS) CsPbI₃ bilayer is developed to stabilize the α phase via a single‐step film deposition process. The spontaneously upward migration of (adamantan‐1‐yl)methanammonium (ADMA) based on the hot‐casting technique causes self‐assembly of the hierarchical morphology for the perovskite layers. Due to the strong steric effect of the surficial ADMA cation, a self‐assembly tiny grain‐sized CsPbI₃ layer is in situ formed at the surface site, which exhibits notably enhanced phase stability by its high surface energy. Meanwhile, a large grain‐sized CsPbI₃ layer is obtained at the bottom site with high charge mobility and low trap density of states, which benefits from the regulated growth rates by the interaction between ADMA and perovskites. The perovskite solar cell (PSC) based on the GGS CsPbI₃ bilayer shows an efficiency of 15.5% and operates stably for 1000 h under ambient conditions. This work confirms that redistributing the surface energy of perovskite films is a facile strategy to stabilize metastable PSCs without the cost of efficiency loss.

中文翻译：

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高效稳定的全无机钙钛矿型太阳能电池的一步沉积法制备α-CsPbI3双层薄膜。

新兴的无机CsPbI ₃钙钛矿是有前途的宽带隙材料，可用于串联太阳能电池，但在环境条件下，它们往往会从黑色α相转变为黄色δ相。本文中，开发了一种梯度晶粒（GGS）CsPbI ₃双层膜，以通过单步膜沉积工艺稳定α相。基于热浇铸技术的（金刚烷-1-基）甲基铵（ADMA）自发向上迁移会导致钙钛矿层的分层形态自组装。由于表面的ADMA阳离子具有很强的空间效应，因此可以自组装形成微小晶粒的CsPbI ₃在表面部位原位形成层，由于其高表面能而使相稳定性显着增强。同时，在底部部位获得了大晶粒尺寸的CsPbI ₃层，具有高电荷迁移率和低态陷阱能级，这得益于ADMA和钙钛矿之间相互作用所调节的生长速率。基于GGS CsPbI ₃双层的钙钛矿太阳能电池（PSC）的效率为15.5％，可在环境条件下稳定运行1000小时。这项工作证实，重新分布钙钛矿薄膜的表面能是在不损失效率的情况下稳定亚稳PSC的简便策略。