Proton Transfer‐Driven Modification of 3D Hybrid Perovskites to Form Oriented 2D Ruddlesden–Popper Phases

Photoluminescence Modulation of Ruddlesden-Popper Perovskite via Phase Distribution Regulation

The intrinsic chaotic phase distribution in Ruddlesden-Popper Perovskite (RPP) hinders its further improvement of photoluminescence (PL) emission and limits its application in optical devices. In this work, we achieve the phase distribution regulation of RPP by varying the composition ratio of organic bulky spacer cations 1-naphthylmethylamine (NMA) and phenylethyl-ammonium (PEA), which is controllable and nondestructive for structures of RPP. By suppressing the small n-phase, the PL intensity emission of RPP is further improved. Through the time-resolved PL (TRPL) measurements, we find the PL lifetime of the sample with 66% PEA concentration increases with the temperature initially and possesses the highest values of τ1 and τ2 at ~255 K, indicating the immediate state assisting exciton radiative recombination, and it can be modulated by phase manipulation in RPP. The immediate state may outcompete other non-radiative decay channels for excited carriers, leading to the PL enhancement in RPP, and broadening its further application.

Halide Perovskite Crystallization Processes and Methods in Nanocrystals, Single Crystals, and Thin Films

Halide perovskite semiconductors with extraordinary optoelectronic properties have been fascinatedly studied. Halide perovskite nanocrystals, single crystals, and thin films have been prepared for various fields, such as light emission, light detection, and light harvesting. High-performance devices rely on high crystal quality determined by the nucleation and crystal growth process. Here, the fundamental understanding of the crystallization process driven by supersaturation of the solution is discussed and the methods for halide perovskite crystals are summarized. Supersaturation determines the proportion and the average Gibbs free energy changes for surface and volume molecular units involved in the spontaneous aggregation, which could be stable in the solution and induce homogeneous nucleation only when the solution exceeds a required minimum critical concentration (C_min ). Crystal growth and heterogeneous nucleation are thermodynamically easier than homogeneous nucleation due to the existent surfaces. Nanocrystals are mainly prepared via the nucleation-dominated process by rapidly increasing the concentration over C_min , single crystals are mainly prepared via the growth-dominated process by keeping the concentration between solubility and C_min , while thin films are mainly prepared by compromising the nucleation and growth processes to ensure compactness and grain sizes. Typical strategies for preparing these three forms of halide perovskites are also reviewed.

Releasable Water Charge-Trapping and Water-Resistant Photodetection using 1D Perovskitoid Hydrate Single Crystal

Hydrates of hybrid organic-inorganic perovskites have been discovered with MAPbI₃ and are proved to be unstable in atmosphere. However, the influence of water molecules on the performance of optoelectronic devices is still not fully understood. Here, using a dication, 2-(dimethylamino) ethylamine (DMEN²⁺ ), a stable quasi-1D perovskitoid hydrate single crystal is designed and successfully synthesized, which is formulated as DMENPb₂ I₆ ·H₂ O. In this design, both corner-sharing and edge-sharing connectivity are adopted, and water molecules are connected with the crystal through hydrogen bonding. It is discovered that such water sites distributed along the inorganic chains function both as charge traps and as releasable charge stocks. Optical excitation that overcomes the potential wells formed on these water sites may release these stocked charges and facilitate enhanced transportable charge density. Meanwhile, exciton diffusion and charge transport are strongly confined in the 1D transport channels. Above mechanisms are verified both by the transient absorption spectroscopy and by the photodetection performance. This introduces a new design strategy with a trapping-stock-releasing-transport roadmap for perovskitoid materials. Excellent water resistance endows this material with more advantages in the development of a new generation of optoelectronic devices.