Journal of Photochemistry and Photobiology (Jun 2022)
Are the emission quantum yields of cesium plumbobromide perovskite nanocrystals reliable metrics for their quality?
Abstract
The impact of halide perovskites on photonics, optoelectronics and energy science is indisputable. The pursuit of perovskite nanomaterials has open roads for explorations where large surface-to-volume ratios are paramount. While the solution-phase synthesis of most nanoparticles is relatively easy, the cleaning steps for obtaining populations of high-quality nanocrystals in good yields tend to present some challenges. As an extensive number of reports show, the quality of photoluminescent nanoparticles usually correlates with increased optical-emission quantum yields. Herein, we examine the products from the cleaning steps, involving centrifugation and resuspension washes, of an established procedure for preparing cesium plumbobromide nanocrystals. The photoluminescence quantum yields of the collected nanocrystals drops by about 10% to 30% after each wash. At the same time, the average exciton lifetime increases by about a factor of four, which reflects a decrease in the radiative-decay rates by about factor of five, while the non-radiative ones increase by less than a factor of two. Further analysis indicates that decreasing the particles size, along with changing their morphology, alters some of the exciton traps, or “quenching” sites, on them. This size decrease, along with changes that accompany it, shorten the exciton lifetimes while enhancing the limited spatial overlap between the holes and the electrons of the excitons and considerably increasing the radiative rates of deactivation. These findings do not suggest that good quality nanoparticles should not necessarily manifest high emission quantum yields. Rather, they point to the complexity of nanomaterials, due to their inherent heterogeneity, that warrants multimodal analysis for understanding the exciton dynamics, while correlating it to observed structural characteristics.
