A-Site Effect on the Oxidation Process of Sn-Halide Perovskite: First-Principles Calculations

Abstract

Tin-halide perovskite solar cells (Sn-PSCs) are promising candidates as an alternative to toxic lead-halide PSCs. However, Sn2+ is easily oxidized to Sn4+, so Sn-PSCs are unstable in air. Here, we use first-principles density functional theory calculations to elucidate the oxidation process of Sn2+ at the surface of ASnBr3 [A = Cs or CH3NH3 (MA)]. Regardless of the A-site cation, adsorption of O2 leads to the formation of SnO2, which creates a Sn vacancy at the surface. The A-site cation determines whether the created vacancies are stabilized in the bulk or at the surface. For CsSnBr3, the Sn vacancy is stabilized at the surface, so further oxidation is limited. For MASnBr3, the Sn vacancy moves into bulk region, so additional Sn is supplied to the surface; as a result, a continuous oxidation process can occur. The stabilization of Sn vacancy is closely related to the polarization that the A-site cation causes in the system.

DMSO‐Free Solvent Strategy for Stable and Efficient Methylammonium‐Free Sn–Pb Alloyed Perovskite Solar Cells

“…In terms of such storage conditions, environmental factor was absent, thus the degradation would mainly result from internal factors, such as the unstable Sn 4+ vacancies in perovskite components. [44] The corresponding results were recorded in Figure S17 (Supporting Information). Here, the devices modified with D/P retained 95.9% of its initial PCE after 2000 h. In contrast, the control devices retained only 87.1% of its initial efficiency.…”

Resolving Mixed Intermediate Phases in Methylammonium-Free Sn–Pb Alloyed Perovskites for High-Performance Solar Cells

“…6i, k). Under these storage conditions, environmental factors were absent, so the main degradation would have resulted from internal factors, such as any unstable perovskite components containing Sn 4+ and the acid nature of PEDOT:PSS [65][66][67][68]. Here, our single-junction device modified with D-HLH retained 94.1% of its initial PCE after 3000 h, while the tandem device maintained 93% of its PCE after more than 1000 h; in contrast, the control single-junction and tandem devices retained only 63.9% and 41.1%, respectively, of their initial PCEs.…”

Surface energy and surface stability of cesium tin halide perovskites: a theoretical investigation

“…The degradation product of Sn-perovskites exposed to ambient air is suggested to be environment-friendly SnO 2 . 14,15 The PCE of Sn-perovskite solar cells has been raised up to 14.81%. 10,[16][17][18] However, the development of Sn-perovskitebased solar cells also encounters bottlenecks.…”

“…21 The oxidation and the degradation of Sn-perovskites generally initiate at the surface. 15,22 Therefore, understanding the surface properties of Sn-perovskites is extremely important, especially thermodynamic stability and surface energy.…”