Degradation mechanism of hybrid tin-based perovskite solar cells and the critical role of tin (IV) iodide

Abstract

Tin perovskites have emerged as promising alternatives to toxic lead perovskites in next-generation photovoltaics, but their poor environmental stability remains an obstacle towards more competitive performances. Therefore, a full understanding of their decomposition processes is needed to address these stability issues. Herein, we elucidate the degradation mechanism of 2D/3D tin perovskite films based on (PEA)0.2(FA)0.8SnI3 (where PEA is phenylethylammonium and FA is formamidinium). We show that SnI4, a product of the oxygen-induced degradation of tin perovskite, quickly evolves into iodine via the combined action of moisture and oxygen. We identify iodine as a highly aggressive species that can further oxidise the perovskite to more SnI4, establishing a cyclic degradation mechanism. Perovskite stability is then observed to strongly depend on the hole transport layer chosen as the substrate, which is exploited to tackle film degradation. These key insights will enable the future design and optimisation of stable tin-based perovskite optoelectronics.

Fluoride Chemistry in Tin Halide Perovskites

“…The conversion of SnI 4 into SnF 4 will also prevent the SnI 4 ‐driven degradation pathways recently described by Lanzetta et al. [36] Furthermore, the selective complexation of Sn IV as SnF 4 may hinder its ability to form any perovskite‐like complex in solution. It has been widely reported for SnF 2 that this material's excess tends to undergo phase separation.…”

Emission‐Color‐Tunable Pb−Sn Alloyed Single Crystals with High Luminescent Efficiency and Stability

“…Given the well-known extreme vulnerability of Sn 2+ -based perovskite materials to moisture, the air stability of (C 10 NH 22 ) 2 Pb 0.4 Sn 0.6 Br 4 phosphors is surprising. [41,42] After being stored in ambient air for half a year without any encapsulation, the phase integrity and emission color of (C 10 NH 22 ) 2 Pb 0.4 Sn 0.6 Br 4 are intact, and more importantly an impressively PLQY as high as 78% is still observed (Figure S22, Supporting Information). By contrast, monometallic (C 10 NH 22 ) 2 SnBr 4 degrades after exposing in air for several days due to the oxidation of Sn 2+ to Sn 4+ , as confirmed by the PL, PXRD XPS, and UV-vis measurements (Figure S23, Supporting Information).…”

A Review of Three-Dimensional Tin Halide Perovskites as Solar Cell Materials

“…SnI 4 is detrimental to tin perovskites. Its role in the degradation of perovskites (20% phenylethylammonium and 80% formamidinium as organic cations) was further clarified and a mechanism was proposed based on X-ray diffraction, spectroscopy and ab initio simulation techniques 176 . Figure 12 shows the degradation mechanism of tin perovskites under ambient conditions (relative humidity= 38; temperature = 22.9 o C).…”

“…Figure 12 shows the degradation mechanism of tin perovskites under ambient conditions (relative humidity= 38; temperature = 22.9 o C). From Equation 5, the perovskite reacts with oxygen to produce SnI 4 , SnO 2 and AI (A=organic cation) 176…”

“….Based on Equation6, there is a reaction between SnI 4 and AI (A=organic cation) to produce the A 2 SnI 6 , an oxidized variant176 .However, this process takes time, thus the coexistence of the products SnI 4 , SnO 2 and AI (A=organic cation) is more plausible176 .SnI 4 can react with water to form SnO 2 and HI (Equation7)176 .…”