An intriguing reversible band gap narrowing behavior of the lead‐free hybrid perovskite single crystal DMASnI₃ (DMA=CH₃NH₂CH₃⁺) from yellow to black is observed without phase transformation. We discuss the transformation mechanism in detail. More interestingly, the transformed samples in black can rapidly self‐heal into yellow ones when exposed to deionized water (DI water). Contrary to other hybrid perovskites, DMASnI₃ crystals exhibit excellent water phase stability. For example, DMASnI₃ was immersed in DI water for 16 h and no decomposition was observed. Inspired by its excellent water phase stability, we demonstrate a potential eco‐friendly application of DMASnI₃ in photo‐catalysis for H₂ evolution in DI water. We present the first H₂ evolution rate of 0.64 μmol h⁻¹ with good recycling properties for pure DMASnI₃ crystals. After the narrowing process, the optical band gap of DMASnI₃ can be lowered from 2.48 eV to 1.32 eV. Systematical characterizations are applied to investigate their structures and optoelectronic properties. The reversible band gap narrowing behavior and outstanding electrical properties, such as higher carrier mobility and long carrier lifetime show that DMASnI₃ has a great potential for optoelectronic applications.

中文翻译：

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具有出色的相稳定性的Sn基杂化钙钛矿单晶的可逆带隙变窄

观察到无铅杂化钙钛矿单晶DMASnI ₃（DMA = CH ₃ NH ₂ CH ₃ ⁺）从黄色到黑色的有趣的可逆带隙变窄行为，而没有相变。我们将详细讨论转换机制。更有趣的是，当暴露于去离子水（去离子水）中时，黑色的转化样品可以快速自愈成黄色。与其他杂化钙钛矿相反，DMASnI ₃晶体具有出色的水相稳定性。例如，将DMASnI ₃浸入去离子水中16小时，未观察到分解。受到其出色的水相稳定性的启发，我们证明了DMASnI的潜在生态友好应用在去离子水中H ₂析出的光催化作用中位居_第三。我们提出了0.64μmolh ^-1的第一个H ₂析出速率，对于纯DMASnI ₃晶体具有良好的回收特性。在变窄过程之后，可以将DMASnI ₃的光学带隙从2.48 eV降低到1.32 eV。系统表征用于研究其结构和光电性能。可逆的带隙变窄行为和出色的电性能，例如更高的载流子迁移率和更长的载流子寿命，表明DMASnI ₃在光电应用中具有巨大的潜力。