First-Principles Screening of Lead-Free Methylammonium Metal Iodine Perovskites for Photovoltaic Application

Although organo-halide lead perovskite solar cells have achieved outstanding photovoltaic performance in recent years, environmental concern about lead pollutant limits its large-scale commercialization. To address lead-free organo-halide perovskite materials, here we report first-principles screening of different perovskite materials MAXI₃ with consideration of all possible (27 in total) divalent metal ions. Ten kinds of perovskite structures are obtained with a nonzero bandgap, and the others are metallic. Among them, five kinds of perovskite materials (MAXI₃: X = Pb, Sn, Ge, Cd, Be) have appropriate bandgaps as the light-absorbing material in solar cells, in which MACdI₃ and MABeI₃ are reported for the first time. Various corresponding experiments have been carried out to confirm our theoretical predictions

(C₆H₅C₂H₄NH₃)₂GeI₄: A Layered Two-Dimensional Perovskite with Potential for Photovoltaic Applications

Recently, two-dimensional organic–inorganic perovskites have attracted increasing attention due to their unique photophysical properties and high stability. Here we report a lead-free, two-dimensional perovskite, (PEA)₂GeI₄ (PEA = C₆H₅(CH₂)₂NH₃⁺). Structural characterization demonstrated that this 2D perovskite structure is formed with inorganic germanium iodide planes separated by organic PEAI layers. (PEA)₂GeI₄ has a direct band gap of 2.12 eV, in agreement with 2.17 eV obtained by density functional theory (DFT) calculations, implying that it is suitable for a tandem solar cell. (PEA)₂GeI₄ luminesces at room-temperature with a moderate lifetime, exhibiting good potential for photovoltaic applications. In addition, 2D (PEA)₂GeI₄ is more stable than 3D CH₃NH₃GeI₃ in air, owing to the presence of a hydrophobic organic long chain. This work provides a direction for the development of 2D Ge-based perovskites with potential for photovoltaic applications