Compositional engineering of ZnBr2-doped CsPbBr3 perovskite nanocrystals: insights into structure transformation, optical performance, and charge-carrier dynamics

Compositional engineering of CsPbBr3 perovskite nanocrystals (PNCs) via Zn(ii)-doping is an effective way to passivate the defect states, improve the stability, and photoluminescence (PL) efficiency of PNCs for optoelectronic applications. The increase in doping of ZnBr2 results in a gradual transformation of CsPbBr3 into Cs4PbBr6 through the formation of intermediate CsPbBr3-Cs4PbBr(6) heterostructures. The structural transformation is due to the replacement of Pb2+ ions at the B-site with Zn2+ ions supplied by ZnBr2. Furthermore, the presence of additional Br- ions not only facilitates the transition process but also inhibits surface defects in PNCs, leading to an impressive PL quantum yield of 98.6%. The mechanism behind this transformation and the enhancement of optical properties was investigated through experimental characterization techniques. Time-resolved PL and transient absorption spectroscopy revealed the suppression of nonradiative carrier trapping centers and the generation of shallow energy states, facilitating radiative recombination with the addition of ZnBr2. Furthermore, temperature-dependent PL and TRPL studies revealed that radiative recombination and de-trapping were facilitated by temperature changes. At elevated temperatures, ZnBr2-doped PNCs exhibited better color stability than CsPbBr3, making them suitable for application in light-emitting devices. Finally, we developed a white light emitting diode (WLED) using a blue LED, Zn-doped CsPbBr3 PNCs, and K2SiF6:Mn4+, which resulted in the emission of white light with impressive features: a high luminous efficiency of 58 lm W-1, a color rendering index of 80.6, and generated color coordinates of (0.3312, 0.3253) with a correlated temperature of 5584 K, Furthermore, the WLED achieved a wide color gamut, exhibiting 129.74% of the NTSC and 96.88% of the BT-2020.