Comment on Interplay of Structural and Optoelectronic Properties in Formamidinium Mixed Tin-Lead Triiodide Perovskites

Studying optoelectronic properties in FAPb(1-x)Sn(x)I(3) and in FA(0.83)Cs(0.17)Pb(1-x)Sn(x)I(3) perovskites as a function of the lead:tin content, Parrott et al. (2018) and Savill et al. (2020) observed the broadest luminescence linewidth and the largest Stokes shift in mixed compositions with Sn 85%. It is in contrast to the intuitive expectation of the largest effects of alloy disorder for the 50:50 composition. This comment addresses the alloy disorder caused by statistical local spatial fluctuations of the alloy composition and shows that the largest effects of alloy disorder for perfectly random fluctuations in FAPb(1-x)Sn(x)I(3) and FA(0.83)Cs(0.17)Pb(1-x)Sn(x)I(3) are, in fact, expected for x < 0.25 and for x > 0.85. It can be one of the reasons why Pb-rich and Sn-rich Sn-Pb perovskites typically show shorter photoluminescence (PL) lifetimes, broader emission, increased Stokes shifts, reduced PL quantum yield, and higher Urbach tails, compared with their lead-only counterparts.

Automated summary

In the study of optoelectronic properties in FAPb(1-x)Sn(x)I(3) and FA(0.83)Cs(0.17)Pb(1-x)Sn(x)I(3) perovskites as a function of the lead:tin content, researchers observed that the broadest luminescence linewidth and the largest Stokes shift occurred in mixed compositions with Sn 85%, contrary to the intuitive expectation. This comment suggests that the largest effects of alloy disorder are expected for x < 0.25 and x > 0.85 due to statistical local spatial fluctuations of the alloy composition, which could explain why Pb-rich and Sn-rich Sn-Pb perovskites exhibit certain optical properties compared to lead-only counterparts.