Band-Gap Tuning in All-Inorganic CsPb<i>_x</i>Sn_1–<i>x</i>Br₃ Perovskites

Abstract

We investigate all-inorganic perovskite CsPb<i>_x</i>Sn_1-<i>x</i>Br₃ thin films to determine the variations in the band gap and electronic structure associated with the Pb/Sn ratio. We observe that the band gap can be tuned between 1.86 eV (<i>x</i> = 0) and 2.37 eV (<i>x</i> = 1). Intriguingly, this change is nonlinear in <i>x</i>, with a bowing parameter of 0.9 eV; furthermore, a slight band gap narrowing is found for low Pb content (minimum <i>x</i> ∼ 0.3). The wide tunability of the band gap makes CsPb<i>_x</i>Sn_1-<i>x</i>Br₃ a promising material, e.g., for a wide-gap subcell in tandem applications or for color-tunable light-emitting diodes. Employing photoelectron spectroscopy, we show that the valence band varies with the Pb/Sn ratio, while the conduction band is barely affected.