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), MA1−x−y−zFAxCsyRbzPbI3 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 MA1−x−y−zFAxCsyRbzPbI3 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. Incorporation of Cs+ and/or HC(NH2)2+ cations to prototypical CH3NH3PbI3 enhances chemical stabilities of alloyed perovskites under humidity and elevated temperature conditions, while adoptions of cations with longer alkyl chains, such as C4H9NH3+, together with CH3NH3+ can lead to out-of-plane alignments of highly-crystalline 2-D perovskites with increased stability and favored charge transport. [Display omitted]