Progresses on Novel B‐Site Perovskite Nanocrystals

Abstract

Halide perovskite materials have emerged as a new type of optoelectronic materials serving as key active layer for next‐generation photovoltaics, light‐emitting diodes, lasers, and photodetectors. Manipulating the crystal size toward the so‐called perovskite nanocrystals (PNCs) will endow new properties due to quantum confinement and ligand effect. However, like their bulk crystalline film, the lead toxicity is still one of decisive concerns that holds‐back their public acceptance. Design of lead‐free (LF) PNCs requires efforts on replacing the B‐site element with other metal candidates from the periodic table. In the past half‐decade, hundreds of new LF PNCs have been developed with various sizes, subdimensionalities, ligands, and electron/quantum confinements, as well as wide applications. Although the lead‐based perovskites still dominate the ongoing research fields, the LF PNCs can have a large potential if novel nonlead B‐site element is introduced to render new type of LF PNCs material that is more stable, less toxic, and more efficient in device performance. In this review, recent progresses on the LF PNCs are revisited to seek these opportunities. The paper is organized in subtopics on material structures, synthesis, properties, and their state‐of‐the‐art applications of different LF PNCs, coupled with an in‐depth discussion on the perspectives and challenges.

Recent Progress in Mixed A‐Site Cation Halide Perovskite Thin‐Films and Nanocrystals for Solar Cells and Light‐Emitting Diodes

“…The mixed A‐cation LHP NCs can be synthesized directly using the mixture of desired A‐cation precursors or by applying post‐synthetic A‐cation exchange and cross‐exchange on pre‐synthesized mono‐cation LHP NCs, as illustrated in Figure . The direct synthesis can be carried out by classical methods such as hot‐injection [ 48–175 ] or reprecipitation [ …”

“…Meanwhile, the field of colloidal perovskite NCs has received increasing attention owing to their high photoluminescence quantum yield (PLQY), facile synthesis, and enhanced stability over bulk thin films. [6,[48][49][50][51][52][53][54][55] Over the last 7 years, research on perovskite NCs has explored their synthesis, surface chemistry, optical and electronic properties along with their applications. [6,14,50,[56][57][58] The concept of A-site cation compositional engineering has also been extended to colloidal LHP NCs to fine-tune their optical properties as well as to improve their phase stability.…”

Effects of Electron–Phonon Coupling and Spin–Spin Coupling on the Photoluminescence of Low-Dimensional Metal Halides

“…According to the connectivity of metal halide polyhedron units, their low-dimensional materials can be classified into 2D quantum wells, 1D quantum wires, and 0D clusters at the molecular level . The local confinement effect and related electron–phonon coupling as well as the cluster separation-dependent exchange interactions modulate the electronic states and properties significantly, which supplies giant opportunities to design new materials and to find novel applications . Different from common 3D lead halide perovskites, many LDMHs generally exhibit a broad emission band and a large Stokes shift, especially when larger organic molecules are used for incorporation. , With more in-depth research on perovskite-type materials, many scientists have tried to reveal their intrinsic or detailed microscopic interactions and the related photophysical properties and to expand their applications in optoelectronic devices based on the extraordinary luminescence properties.…”

Simultaneous Enhancement of the Luminescence Intensity and Stability of Deep-Red CsPbI3 Perovskite Quantum Dots Achieved by a Doping Strategy

“…However, the inadequate matching between Pb 2+ and I – in CsPbI 3 PQDs results in an extremely unstable structure, and CsPbI 3 with deep-red emission can be easily converted from the α phase to the non-luminescent δ phase. , In addition, the I – ions in CsPbI 3 are prone to form trap states, and the nonradiative recombination probability of excitons increases, leading to a serious reduction of the luminescence efficiency of CsPbI 3 PQDs . Therefore, the development of a highly efficient deep-red CsPbI 3 phosphor with eminent stability and high color purity is currently a research focus of inorganic PQD luminescent materials. , …”

“…18 Therefore, the development of a highly efficient deep-red CsPbI 3 phosphor with eminent stability and high color purity is currently a research focus of inorganic PQD luminescent materials. 19,20 To date, many researchers have adopted various methods to enhance the luminescence performance and stability of CsPbX 3 PQDs, such as composition regulation, 20 surface modification, 21,22 matrix encapsulation, 23 and elemental doping. 24 In particular, the elemental doping route can not only effectively improve the luminescence efficiency but also tackle intrinsic problems such as self-absorption and sensitivity to chemical, thermal, and photochemical disturbances of pure PQDs.…”