Progresses on Novel B-Site Perovskite Nanocrystals

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.