The properties, photovoltaic performance and stability of visible to near-IR all inorganic perovskites

Abstract

Hybrid metal halide perovskites have seen an exponential increase in the scientific community due to their successful introduction in solar cells. However, these materials are known to suffer from thermal instability, toxicity and limited absorption range. One way to overcome these obstacles is by substituting the organic cation with an inorganic one and by replacing the lead with tin, which can shift the absorbance to the near infra-red (NIR). In this work we synthesized several compositions of all inorganic CsSn_yPb_1−yBr_xI_3−x (0 ≤ y ≤ 1, 0 ≤ x ≤ 3) perovskites, achieving a wide band gap range from 1.3 eV to 1.75 eV. It was found that Sn stabilizes the CsPbI₃ black photovoltaic (PV) active phase and at the same time shifts the absorbance to the NIR. Although some of these perovskite compositions are already known, here we analyzed in detail their physical and electronic properties. Hall effect measurements show an increase in the carrier concentration and Hall mobility with the addition of Sn. Interestingly, the Hall mobility is five times higher for CsSnI₃ than in the case of having just 10% Pb and 90% Sn in the perovskite structure. Ultraviolet photoemission spectroscopy (UPS) and density functional theory (DFT) calculations reveal the energy level position and phase mixing, which explain the reduction in the photovoltaic performance with the addition of Sn. The best PV performance of 12.7% efficiency was achieved in the case of an 80 : 20 Pb : Sn ratio, which is one of the highest PCEs reported for similar perovskite compositions.