Mixed Metal Halide Perovskite CsPb1-xSnxBr3 Quantum Dots: Insight into Photophysics from Photoblinking Studies

Mixing different metal ions in the B site of ABX₃ perovskites offers a promising approach to address challenges related to toxicity, stability and performance in optoelectronic applications. One such example is CsPb_1-xSn_xBr₃ which addresses the toxicity issue posed by lead while allowing us to tune optoelectronic properties such as band gap. In this work, nearly monodisperse CsPb_1-xSn_xBr₃ quantum dots (QDs) synthesized with variable Pb/Sn compositions, i.e. CsPbBr₃, CsPb_0.9Sn_0.1Br₃ and CsPb_0.7Sn_0.3Br₃. Photoluminescence quantum yield (PLQY) of CsPb_1-xSn_xBr₃ first increases for x=0.1 and then decrease for x=0.3 with respect to x=0. Such effect of Sn incorporation on the PLQY investigated using photoblinking studies which revealed three level blinking statistics namely ON, GRAY and OFF. These results along with the excited state lifetime measurements enabled us to understand charge carrier dynamics in CsPb_1-xSn_xBr₃ QDs. Based on our findings we propose that the photogenerated hot electrons of Sn enhances the PLQY by filling TRAP states centered on Pb, which otherwise promote non-radiative relaxations in the Sn free CsPbBr₃. However, at higher Sn concentrations, non-radiative recombination becomes more pronounced, reducing the PLQY.