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

Abstract

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–Cs₄PbBr₆ 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.