OPTOELECTRICAL PROPERTIES AND PHOTOSTABILITY OF CsPbBr3 QUANTUM DOTS

Metal halide perovskite QDs have a great potential for displays and lighting because of their exceptional optoelectronic characteristics associated with quantum confinement effect. However, the stability in the environment during the applications of halide perovskite QDs remains a significant challenge, impeding their practicality and lowering their commercial scalability. High-temperature methods are well-established for producing doped perovskite QDs, the influence of room-temperature synthesis on thermal, size-dependent optical properties, and long-term stability remains inadequately understood. Also, there is a demand for strategies to increase the absorption of light, reduce trap states, and modify the energy levels of perovskite QDs. In this study, we explore practical methods to improve the stability of CsPbBr3 QDs with doping and ligand exchange. We developed a room temperature (18oC) procedure for the fabrication of blue-emitted Cu-doped CsPbBr3 QDs with a progressive red shift (~2nm) caused by the increase of particle sizes, utilizing ligand-assisted reprecipitation (LARP) and ultrasonication. Increasing copper doping leads to higher micro-strain, smaller Stokes shift, the decrease of photoluminescence quantum yield (PLQY) (from ~48% to 21%) due to defect-induced non-radiative traps, and a slight reduction of the energy gap (from 2.701 eV to 2.691 eV). Higher doping also improves thermal stability but introduces surface defects or trap states when exceeding 10% of Cu doping, as evidenced by side-peak emissions in photostability tests. A facile method conducted at 35oC is used for enhancing the stability of CsPbBr3 QDs by ligand exchange with didodecyl dimethylammonium bromide (DDAB), which resulted in green emission with a blue shift in photoluminescence (~5-7nm), a higher photoluminescence quantum yield (PLQY) of from ~21% to 57%, and better stability under thermal and ambient conditions by retaining PL intensity by ~66% and 52% respectively. These enhancements are attributed to the effective passivation of surface defects by DDAB, leading to reduced nonradiative recombination. These approaches aim to enhance the photostability of halide perovskite QDs, mitigate surface defects and non-radiative recombination and thereby enhance its optical properties.