Cation engineering on lead iodide perovskites for stable and high-performance photovoltaic applications

Perovskite solar cells (PSCs) based on methylammonium lead iodide (CH₃NH₃PbI₃) have shown unprecedentedly outstanding performance in the recent years. Nevertheless, due to the weak interaction between polar CH₃NH₃ ⁺ (MA⁺) and inorganic PbI₃ ⁻ sublattices, CH₃NH₃PbI₃ dramatically suffers from poor moisture stability, thermal decomposition and device hysteresis. As such, strong electrostatic interactions between cations and anionic frameworks are desired for synergistic improvements of the abovementioned issues. While replacements of I⁻ with Br⁻ and/or Cl⁻ evidently widen optical bandgaps of perovskite materials, compositional modifications can solely be applied on cation components in order to preserve the broad absorption of solar spectrum. Herein, we review the current successful practices in achieving efficient, stable and minimally hysteretic PSCs with lead iodide perovskite systems that employ photoactive cesium lead iodide (CsPbI₃), formamidinium lead iodide (HC(NH₂)₂PbI₃, or FAPbI₃), MA_{1− x − y − z}FA_xCs_yRb_zPbI₃ mixed-cation settings as well as two-dimensional butylammonium (C₄H₉NH₃ ⁺, or BA⁺)/MA⁺, polymeric ammonium (PEI⁺)/MA⁺ co-cation layered structures. Fundamental aspects behind the stabilization of perovskite phases α-CsPbI₃, α-FAPbI₃, mixed-cation MA_{1 − x − y − z}FA_xCs_yRb_zPbI₃ and crystallographic alignment of (BA)₂(MA)₃Pb₄I₁₃ for effective light absorption and charge transport will be discussed. This review will contribute to the continuous development of photovoltaic technology based on PSCs.