One-step ultrasonic irradiation method for Bi-doped CsPbI2Br nanocrystals: An interplay of doping mechanisms

Doping metal ions into a perovskite lattice is an effective strategy for tailoring the intrinsic properties of perovskite nanocrystals (NCs). Herein, we report the synthesis of red emitting Bi³⁺ doped CsPbI₂Br nanocrystals (NCs) using a one-step ultrasonic irradiation method. Thorough investigations of the effect of Bi³⁺ doping on the photophysical properties of CsPbI₂Br NCs were presented which indicated that the Bi³⁺ ions can be incorporated at interstitial sites, at substitutional site or at both the sites by carefully optimising the feeding concentration of Bi³⁺ ions in the precursor solution. Structural studies showed that substitutional doping was observed for 3.4 % Bi³⁺ doped CsPbI₂Br NCs which resulted in the lattice contraction and shortened the bond length of B–X bond, thereby suppressing the distortion of [BX₆]^4- octahedra of ABX₃ perovskite structure, thus, improved the photophysical properties of CsPbI₂Br NCs. For 3.4 % Bi³⁺ doped CsPbI₂Br NCs, a reduction in the bandgap and 82 % increase in average PL decay time were observed as compared to that of the pure CsPbI₂Br NCs. The prepared Bi-doped CsPbI₂Br NCs with tuned bandgap and enhanced optical properties presented here could be used as potential candidate for future photovoltaic applications.