Colloidal metal halide perovskite nanocrystals: a promising juggernaut in photovoltaic applications

Metal halide perovskites have received considerable attention in recent years in view of their successful utilization in the research field of photovoltaics. While nanostructured semiconducting materials have been widely investigated in a variety of applications, colloidal metal halide perovskite nanocrystals are distinguished as a family of versatile and attractive building blocks in optoelectronic applications owing to their high photoluminescence quantum yields, wieldy tunability of optical properties, and sterling size-dispersion and shape-uniformity. In this review, recent developments in the direct synthesis and reactions based on the ion-exchange of colloidal metal halide perovskite nanocrystals are discussed first. Subsequently, particular emphases are placed on the morphology-controlled synthesis and self-assembly performance of colloidal metal halide perovskite nanocrystals. In addition, the optoelectronic properties of colloidal metal halide perovskite nanocrystals such as the tunable band gaps, the innate tolerance towards high density of defects, and the multiple exciton generation are explored in detail. Finally, the progresses in the applications of colloidal metal halide perovskite nanocrystals in photovoltaic devices are presented. With a focus of preparing high-quality colloidal metal halide perovskite nanocrystals to stimulate the development of highly efficient photovoltaic devices, the intention of this review is to introduce the current status of this type of novel optoelectronic candidate to researchers from various areas and to motivate them to devote more efforts to boost the performance of related photovoltaic devices to a competitive stage.