Mahui

Metal halide perovskites are a promising platform in light of their excellent charge transport and bandgap tunability. Especially low‐dimensional perovskites, spatially confined at the nanoscale, have further extended the degree of tunability and functionalities. Advances in perovskite materials for light emission applications and their materials properties, photophysical and electrooptic spectroscopic properties, and device performance are discussed.

Abstract

Next‐generation displays require efficient light sources that combine high brightness, color purity, stability, compatibility with flexible substrates, and transparency. Metal halide perovskites are a promising platform for these applications, especially in light of their excellent charge transport and bandgap tunability. Low‐dimensional perovskites, which possess perovskite domains spatially confined at the nanoscale, have further extended the degree of tunability and functionality of this materials platform. Herein, the advances in perovskite materials for light‐emission applications are reviewed. Connections among materials properties, photophysical and electrooptic spectroscopic properties, and device performance are established. It is discussed how incompletely solved problems in these materials can be tackled, including the need for increased stability, efficient blue emission, and efficient infrared emission. In conclusion, an outlook on the technologies that can be realized using this material platform is presented.

Inorganic halide perovskite nanostructures are developed. These building blocks are promising in various applications including lasers, solar cells, light‐emitting diodes, and thermoelectric devices.

Abstract

Halide perovskites have emerged as a class of promising semiconductor materials owing to their remarkable optoelectronic properties exhibiting in solar cells, light‐emitting diodes, semiconductor lasers, etc. Inorganic halide perovskites are attracting increasing attention because of the higher stability toward moisture, light, and heat as compared with their organic–inorganic hybrid counterparts. In particular, inorganic halide perovskite nanomaterials provide controllable morphology, tunable optoelectronic properties, and improved quantum efficiency. Here, the development controlled synthesis of desired inorganic halide perovskite nanostructures by various chemical approaches is described. Utilizing these nanostructures as platforms, anion exchange chemistry for wide compositional and optical tunabilities is described, and the rich structural phase transition phenomenon and mechanism investigated systematically. Furthermore, these nanostructures and extracted knowledge are applied to design photonic, photovoltaic, and thermoelectric devices. Finally, future directions and challenges toward improvement of the optical, electrical, and optoelectronic properties, exploration of the anion and cation exchange kinetics, and alleviation of the stability and toxicity issues in inorganic lead based halide perovskites are discussed to provide an outlook on this promising field.

A novel cryogenic process has universal applicability to prepare mixed perovskite films. Excellent film quality and consequently promising device performance result from decoupling of nucleation and crystallization phases during the formation of perovskites. The cryogenic temperature suppresses premature reactions of the precursors and prevents premature coalescence of nuclei into large crystallites, enabling uniform film formation following the blow‐drying and annealing processes.

Abstract

A cryogenic process is introduced to control the crystallization of perovskite layers, eliminating the need for the use of environmentally harmful antisolvents. This process enables decoupling of the nucleation and the crystallization phases by inhibiting chemical reactions in as‐cast precursor films rapidly cooled down by immersion in liquid nitrogen. The cooling is followed by blow‐drying with nitrogen gas, which induces uniform precipitation of precursors due to the supersaturation of precursors in the residual solvents at very low temperature, while at the same time enhancing the evaporation of the residual solvents and preventing the ordered precursors/perovskite from redissolving into the residual solvents. Using the proposed techniques, the crystallization process can be initiated after the formation of a uniform precursor seed layer. The process is generally applicable to improve the performance of solar cells using perovskite films with different compositions, as demonstrated on three different types of mixed halide perovskites. A champion power conversion efficiency (PCE) of 21.4% with open‐circuit voltage (V _OC) = 1.14 V, short‐circuit current density ( J _SC) = 23.5 mA cm⁻², and fill factor (FF) = 0.80 is achieved using the proposed cryogenic process.

A pseudo‐3D CH₃CH₂CH₂NH₃PbI₃ perovskite film is deposited by a scalable dip‐coating technique with high surface coverage, and then conversed to a high‐quality 3D CH₃NH₃PbI₃ perovskite film via an organic‐cation displacement approach. With the MAPbI₃ film as the light absorber, planar perovskite solar cells are fabricated, affording stabilized power conversion efficiencies of 19.27% and 15.68% for 0.09 and 5.02 cm² devices, respectively.

Abstract

Methylammonium iodide (MAI) and lead iodide (PbI₂) have been extensively employed as precursors for solution‐processed MAPbI₃ perovskite solar cells (PSCs). However, the MAPbI₃ perovskite films directly deposited from the precursor solutions, usually suffer from poor surface coverage due to uncontrolled nucleation and crystal growth of the perovskite during the film formation, resulting in low photovoltaic conversion efficiency and poor reproducibility. Herein, propylammonium iodide and PbI₂ are employed as precursors for solution deposition of propylammonium lead iodide (PAPbI₃) perovskite film. It is found that the precursors have good film formability, enabling the deposition of a large‐area and homogeneous PAPbI₃ perovskite film by a scalable dip‐coating technique. The dip‐coated PAPbI₃ film is then subjected to an organic‐cation displacement reaction, resulting in MAPbI₃ film with high surface coverage and crystallinity. With the MAPbI₃ film as the light absorber, planar PSCs are fabricated, and stabilized power conversion efficiencies of 19.27% and 15.68% can be achieved for the devices with active areas of 0.09 and 5.02 cm², respectively. The technology reported here provides a robust and efficient approach to fabricate large‐area and high‐efficiency perovskite cells for practical application.

The sensitive detection of X‐rays using devices based on metal halide perovskite semiconductors embodies a rapidly emerging field of research. The photophysical pathways within a single‐crystal Cs₂AgBiBr₆ detector exhibiting high sensitivity to X‐rays are detailed. By evaluating carrier‐recombination pathways at both high and low temperatures, the dramatic enhancements to performance realized upon cooling the device are elucidated.

Abstract

The sensitive detection of X‐rays embodies an important research area, being motivated by a common desire to minimize the radiation doses required for detection. Among metal halide perovskites, the double‐perovskite Cs₂AgBiBr₆ system has emerged as a promising candidate for the detection of X‐rays, capable of high X‐ray stability and sensitivity (105 μC Gy⁻¹ cm⁻²). Herein, the important photophysical pathways in single‐crystal Cs₂AgBiBr₆ are detailed at both room (RT) and liquid‐nitrogen (LN₂T) temperatures, with emphasis made toward understanding the carrier dynamics that influence X‐ray sensitivity. This study draws upon several optical probes and an RT excitation model is developed which is far from optimal, being plagued by a large trap density and fast free‐carrier recombination pathways. Substantially improved operating conditions are revealed at 77 K, with a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. The temperature dependence of a single‐crystal Cs₂AgBiBr₆ X‐ray detecting device is characterized and a strong and monotonic enhancement to the X‐ray sensitivity upon cooling is demonstrated, moving from 316 μC Gy⁻¹ cm⁻² at RT to 988 μC Gy⁻¹ cm⁻² near LN₂T. It is concluded that even modest cooling—via a Peltier device—will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.

Compositional and orientational control in metal halide perovskites of reduced dimensionality

Compositional and orientational control in metal halide perovskites of reduced dimensionality, Published online: 10 September 2018; doi:10.1038/s41563-018-0154-x

Chemical nature of ferroelastic twin domains in CH₃NH₃PbI₃ perovskite

Chemical nature of ferroelastic twin domains in CH₃NH₃PbI₃ perovskite, Published online: 27 August 2018; doi:10.1038/s41563-018-0152-z