Mixed metal halide perovskite CsPb _{1− x} Sn _x Br ₃ quantum dots: insight into photophysics from photoblinking studies

Mixing different metal ions at the B site of ABX₃ perovskites offers a promising approach for addressing 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 the band gap. In this work, nearly monodisperse CsPb_1-xSn_xBr₃ quantum dots (QDs) were synthesized with variable Pb/Sn compositions, i.e. CsPbBr₃, CsPb_0.9Sn_0.1Br₃ and CsPb_0.7Sn_0.3Br₃. The photoluminescence quantum yield (PLQY) of CsPb_1-xSn_xBr₃ first increases for x = 0.1 and then decreases for x = 0.3 with respect to x = 0. Such an effect of Sn incorporation on the PLQY was investigated using photoblinking studies which revealed three levels of blinking statistics namely ON, GRAY and OFF. These results along with the excited state lifetime measurements enabled us to understand charge carrier dynamics in the CsPb_1-xSn_xBr₃ QDs. Based on our findings, we propose that the photogenerated hot electrons of Sn enhance the PLQY by filling the 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.