Mixed metal halide perovskite CsPbSnBr quantum dots: insight into photophysics from photoblinking studies.

Mixing different metal ions at the B site of ABX perovskites offers a promising approach for addressing challenges related to toxicity, stability and performance in optoelectronic applications. One such example is CsPbSnBr 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 CsPbSnBr quantum dots (QDs) were synthesized with variable Pb/Sn compositions, CsPbBr, CsPbSnBr and CsPbSnBr. The photoluminescence quantum yield (PLQY) of CsPbSnBr first increases for = 0.1 and then decreases for = 0.3 with respect to = 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 CsPbSnBr 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 CsPbBr. However, at higher Sn concentrations, non-radiative recombination becomes more pronounced, reducing the PLQY.