Reversible Band Gap Narrowing of Sn-Based Hybrid Perovskite Single Crystal with Excellent Phase Stability

An intriguing reversible band gap narrowing behavior of the lead-free hybrid perovskite single crystal DMASnI (DMA=CH NH CH ) 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, DMASnI crystals exhibit excellent water phase stability. For example, DMASnI 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 DMASnI in photo-catalysis for H evolution in DI water. We present the first H evolution rate of 0.64 μmol h with good recycling properties for pure DMASnI crystals. After the narrowing process, the optical band gap of DMASnI 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 DMASnI has a great potential for optoelectronic applications.