Progress in halide-perovskite nanocrystals with near-unity photoluminescence quantum yield

Colloidal halide perovskite nanocrystals (PNCs) are an outstanding case study due to their remarkable optical features, such as a high photoluminescence (PL) quantum yield (PLQY), tunable band gap, and narrow emission. Despite the impressive first reports of PLQYs beyond 70%, it has been observed that PLQY is limited by structural defects arising from labile interactions between the organic capping ligand and the inorganic core. Structural defects acting as trap states are key factors limiting both PNC PLQY and stability. In this review, we present the most studied, common, and alternative protocols to fully compensate for surface defects (e.g., halide vacancies, loss of protective capping ligands) as well as how to increase their stability and PLQY to unity (i.e., 100% when PLQY is expressed as a percentage).