Effect of water on the effective Goldschmidt tolerance factor and photoelectric conversion efficiency of organic-inorganic perovskite: insights from first-principles calculations

Mixed Two-Dimensional Organic-Inorganic Halide Perovskites for Highly Efficient and Stable Photovoltaic Application

Solar cells made of hybrid organic-inorganic perovskite (HOIP) materials have attracted ever-increasing attention due to their high efficiency and easy fabrication. However, issues regarding their poor stability remain a challenge for practical applications. Engineering the composition and structure of HOIP can effectively enhance the thermal stability and improve the power conversion efficiency (PCE). In this work, mixed two-dimensional (2D) HOIPs are systematically investigated for solar-power harvesting using first-principles calculations. We find that their electronic properties depend strongly on the mixed atoms (Cs, Rb, Ge and Pb) and the formation energy is related to the HOIP's composition, where the atoms are more easily mixed in SnI-2D-HOIPs due to low formation energy at the same composition ratio. We further show that optimal solar energy harvesting can be achieved on the solar cells composed of mixed SnI-2D-HOIPs because of reduced bandgaps, enhanced mobility and improved stability. Importantly, we find that the mixed atoms (Cs, Rb, Ge and Pb) with the appropriate composition ratios can effectively enhance the solar-to-power efficiency and show greatly improved resistance to moisture. The findings demonstrate that mixed 2D-HOIPs can replace the bulk HOIPs or pure 2D-HOIPs for applications into solar cells with high efficiency and stability.

Enhanced optical absorption via cation doping hybrid lead iodine perovskites

The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH₂)₂PbI₃ (FAPbI₃) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH₃NH₃PbI₃ (MAPbI₃) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI₃/FAPbI₃ structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI₃/FAPbI₃ is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI₃/FAPbI₃. More importantly, compare with the un-doped tetragonal MAPbI₃/FAPbI₃, the Sn-doped MAPbI₃ and FAPbI₃ have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sn-doped FAPbI₃. The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI₃ make it promising candidates for high-efficient perovskite cells.