Trimethylsulfonium lead triiodide (TMSPbI3) for moisture-stable perovskite solar cells

Abstract

Conventional, high-efficiency, hybrid organic–inorganic perovskites (e.g., methylammonium lead iodide (MAPbI₃) and formamidinium lead iodide (FAPbI₃)) having ammonium-based organic cations exhibit poor moisture stability mainly due to the effective hydrogen bonding interaction of nitrogen in the ammonium-based cations with water molecules. Recently, a sulfonium-based cation, trimethylsulfonium (TMS⁺), has attracted growing attention for the development of moisture-stable hybrid perovskite solar cells (PSCs). This research investigated the photovoltaic performance of trimethylsulfonium lead triiodide (TMSPbI₃) based PSCs and their moisture stability both experimentally and theoretically. The results revealed that TMSPbI₃ exhibited a relatively large optical band gap (E_g = 2.32 eV) and high absorption coefficient (α = 2.30 × 10⁴ cm⁻¹ at 500 nm) with a hexagonal one-dimensional crystal structure. The PSCs with a device structure of FTO/c-TiO₂/m-TiO₂/TMSPbI₃/CuSCN/Au exhibited a power conversion efficiency (PCE) of 2.22% with no hysteresis in the I–V curve, and high moisture stability at ambient temperature (25 ± 3 °C, ca. 50% relative humidity) with a PCE loss of only ca. 4.6% after 500 h. This result could be attributed to the absence of the hydrogen bonding interaction of TMS⁺ with water molecules, leading to the effective stabilization of TMSPbI₃ compared to MAPbI₃ and FAPbI₃, verified by density functional theory calculations.