The effect of surface treatment and polymer matrix on photoluminescence intermittency of strongly confined CsPbBr3 quantum dots

Despite having promising properties such as near unity quantum yield of CsPbBr3 perovskite quantum dots (PQDs), having soft chemical nature along with surface defects make them vulnerable to the deteriorating effects in environment surrounding them. Specifically, surface uncoordinated excess Pb ions related traps are known to be responsible for trion generation in PQDs. Here we have synthesized strongly confined (4.5 nm) CsPbBr3 PQDs and investigated the photoluminescence properties at ensemble and single particle level. The temperature dependent ensemble photoluminescence investigations reveal the stable exciton with exciton binding energy of 119 meV in these strongly confined PQDs. The X-ray photoelectron spectroscopy along with FTIR and time resolved photoluminescence spectroscopic measurements confirm the successful surface treatment of PQDs with sodium thiocyanate (NaSCN) and removal of excess Pb ions. Single particle blinking and spectra were recorded on polystyrene embedded untreated and NaSCN treated PQDs. The stable time dependent single particle spectra were recorded on PQDs embedded in polystyrene, suggest that the polystyrene matrix protects PQDs from photo-bleaching. From the statistical blinking analysis, it was found that NaSCN treatment on PQDs reduces excess surface Pb ions resulting in increased average on-time compared to the untreated PQDs. Our work highlights the importance of strongly confined PQDs with highly stable exciton and the essence of using suitable dielectric matrix for QD immobilization for single QD measurements.