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

TL;DR

This paper challenges previous interpretations of optoelectronic disorder effects in FAPb$_{1-x}$Sn$_x$I$_3$ perovskites, showing that the largest disorder effects occur at compositions with less than 25% or more than 85% tin, not at 50%.

Contribution

It clarifies the expected alloy disorder effects in mixed tin-lead perovskites, indicating that disorder effects are intrinsic at certain compositions and not due to extrinsic factors.

Findings

Largest alloy disorder effects occur at x<0.25 and x>0.85.

Disorder effects are intrinsic and not eliminated by crystal growth.

Contradicts previous assumptions about disorder at 50:50 composition.

Abstract

Studying optoelectronic properties in FAPb$_{1-x}$Sn$_x$I$_3$ perovskites as a function of the lead:tin content, Parrott et al. observed the broadest luminescence linewidth and the largest luminescence Stokes shift in mixed compositions with Sn $ < 25$% and with $> 0.85$%. Since the largest effects of alloy disorder were expected for the 50:50 composition, it was concluded that the revealed disorder effects might arise from extrinsic factors that can be eliminated upon further crystal growth optimization. This comment shows that the largest effects of alloy disorder for perfectly random fluctuations in FAPb$_{1-x}$Sn$_x$I$_3$ perovskite are, in fact, expected for $x < 0.25$ and for $x > 0.85$. Therefore, further crystal growth optimization is futile.