The synthesis of highly luminescent colloidal CsSnX3 (X = halogen) perovskite nanocrystals (NCs) remains a long-standing challenge due to the lack of a fundamental understanding of how to rationally suppress the formation of structural defects that significantly influence the radiative carrier recombination processes. Here, we develop a theory-guided, general synthetic concept for highly luminescent CsSnX3 NCs. Guided by density functional theory calculations and molecular dynamics simulations, we predict that, although there is an opposing trend in the chemical potential-dependent formation energies of various defects, highly luminescent CsSnI3 NCs with narrow emission could be obtained through decreasing the density of tin vacancies. We then develop a colloidal synthesis strategy that allows for rational fine-tuning of the reactant ratio in a wide range but still leads to the formation of CsSnI3 NCs. By judiciously adopting a tin-rich reaction condition, we obtain narrow-band-emissive CsSnI3 NCs with a record emission quantum yield of 18.4%, which is over 50 times larger than those previously reported. Systematic surface-state characterizations reveal that these NCs possess a Cs/I-lean surface and are capped with a low density of organic ligands, making them an excellent candidate for optoelectronic devices without any postsynthesis ligand management. We showcase the generalizability of our concept by further demonstrating the synthesis of highly luminescent CsSnI2.5Br0.5 and CsSnI2.25Br0.75 NCs. Our findings not only highlight the value of computation in guiding the synthesis of high-quality colloidal perovskite NCs but also could stimulate intense efforts on tin-based perovskite NCs and accelerate their potential applications in a range of high-performance optoelectronic devices.
Cesium lead halide perovskite nanocrystals (NCs) have emerged as promising luminescent materials for a range of applications. However, the creation of highly luminescent violet-emitting CsPbCl3 NCs mostly relies on doping of a limited number of small-sized metal ions or post-synthetic surface treatment of NCs. Alkaline-earth (AE) metals (e.g., Ca2+, Sr2+, and Ba2+) have been proposed to be able to substitute Pb2+ in halide perovskites, yet it remains incompletely understood whether AE metal ions can be incorporated into the perovskite lattice or can be merely situated at the surface. Here, we explore the possibility of using AE metal ions for the suppression of the formation of trap centers, which leads us to develop a one-pot synthetic passivation strategy to boost the violet-emitting efficiency of CsPbCl3 NCs through the creation of a Ca2+/Sr2+ involved passivation layer. The photoluminescence quantum yield of violet emission reaches 77.1% by incorporating an optimal amount of Ca2+. A wide range of optical and structural characterizations, coupled with first-principles calculations, aid in clarifying the underlying mechanism for the AE-metal-dependent passivation of CsPbCl3 NCs. Specifically, based on the experimental and theoretical results, a model is proposed for the observed abnormal incorporation phenomenon of AE2+ ions in NCs (i.e., Ba2+ can be incorporated into the core of NCs, Ca2+/Sr2+ can only be at/near the surface, while Mg2+ can neither be in the core nor at the surface). We believe that the knowledge gained here may not only offer a new perspective to obtain high-efficiency violet-emitting perovskite NCs through a one-pot synthetic passivation but can also help elucidate the functions that AE2+ ions play in the optimization of perovskite optoelectronic devices.
Zero-dimensional (0D) hybrid metal halides have emerged as a new generation of luminescent phosphors owing to their high radiative recombination rates, which, akin to their three-dimensional cousins, commonly demonstrate thermal quenching of luminescence. Here, we report on the finding of antithermal quenching of luminescence in 0D hybrid metal halides. Using (C 9 NH 20 ) 2 SnBr 4 single crystals as an example system, we show that 0D metal halides can demonstrate antithermal quenching of luminescence. A combination of experimental characterizations and first-principles calculations suggests that antithermal quenching of luminescence is associated with trap states introduced by structural defects in (C 9 NH 20 ) 2 SnBr 4 . Importantly, we find that antithermal quenching of luminescence is not only limited to (C 9 NH 20 ) 2 SnBr 4 but also exists in other 0D metal halides. Our work highlights the important role of defects in impacting photophysical properties of hybrid metal halides and may stimulate new efforts to explore metal halides exhibiting antithermal quenching of luminescence at higher temperatures.
Doping engineering has emerged as one of the most powerful approaches to impart new optical and electronic properties to halide perovskite nanocrystals (NCs). However, the impact of dopants on the structure of perovskite NCs remains poorly understood. Here, we report on the finding of dopinginduced structural phase transitions occurring in all-inorganic perovskite NCs. Using Ni 2+ -doped CsPbCl 3 NCs as a model system, we show that Ni 2+ doping causes the coexistence of dual subdomains of cubic and orthorhombic phases and inhibits the phase transition from cubic to orthorhombic in NCs with negligible atomic vacancies as the temperature decreases. Car− Parrinello molecular dynamics simulations reveal that the dopinginduced structural phase transition results from the dopantenabled release of lattice strain and a temperature-insensitive local structural change in the doped region of NCs. Since size mismatch between dopants and replaced ions widely exists in doped functional materials, our finding may not be limited to halide perovskite NCs, but could have implications even for other classes of doped NCs and bulk materials.
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