Low‐dimensional luminescent lead halide perovskites have attracted tremendous attention for their fascinating optoelectronic properties, while the toxicity of lead is still considered a drawback. Herein, we report a novel lead‐free zero‐dimensional (0D) indium‐based perovskite (Cs2InBr5⋅H2O) single crystal that is red‐luminescent with a high photoluminescence quantum yield (PLQY) of 33 %. Experimental and computational studies reveal that the strong PL emission might originate from self‐trapping excitons (STEs) that result from an excited‐state structural deformation. More importantly, the in situ transformation between hydrated Cs2InBr5⋅H2O and the dehydrated form is accompanied with a switchable dual emission, which enables it to act as a PL water‐sensor in humidity detection or the detection of traces of water in organic solvents.

Low‐dimensional lead halide perovskite materials recently have drawn much attention owing to the intriguing broadband emissions; however, the toxicity of lead will hinder their future development. Now, a lead‐free (C4H14N2)2In2Br10 single crystal with a unique zero‐dimensional (0D) structure constituted by [InBr6]3− octahedral and [InBr4]− tetrahedral units is described. The single crystal exhibits broadband photoluminescence (PL) that spans almost the whole visible spectrum with a lifetime of 3.2 μs. Computational and experimental studies unveil that an excited‐state structural distortion in [InBr6]3− octahedral units enables the formation of intrinsic self‐trapped excitons (STEs) and thus contributing the broad emission. Furthermore, femtosecond transient absorption (fs‐TA) measurement reveals that the ultrafast STEs formation together with an efficient intersystem crossing has made a significant contribution to the long‐lived and broad STE‐based emission behavior.

By constructing a ternary cell with a B1:BO-2Cl:BO-4Cl donor:acceptors combination, an outstanding power conversion efficiency (PCE) of 17.0% (certified to be 16.9%) has been realized for all-small-molecule organic solar cells (ASM-OSCs).

The cesium lead halide perovskite nanocrystal (NC) has shown admirable potential in promising optoelectronic applications. However, the notorious toxicity of lead severely hinders its further commercialization. Herein, we report facile synthesis of a lead-free Cs 2 PdBr 6 perovskite NC without the assistance of longchain organic ligand. Such Cs 2 PdBr 6 NCs with an average particle diameter of 2.8 nm and thickness of 1−2 unit cells possess a narrow bandgap of 1.69 eV and outstanding stability toward light, humidity, and heat, which enables it to be a promising photoelectrical material. The charge carrier dynamics are also analyzed via time-resolved photoluminescence decay and transient absorption spectroscopy to guide forthcoming material optimizations. Lastly, a fast anionexchange method is adopted to prepare the Cs 2 PdI 6 NC. Overall, this work inspires an eminent prototype to synthesize ingenious lead-free, narrow-bandgap, and stable perovskite NCs.