Cs2XI2Cl2 (X = Pb, Sn) All‐Inorganic Layered Ruddlesden–Popper Mixed Halide Perovskite Single Junction and Tandem Solar Cells: Ultra‐High Carrier Mobility and Excellent Power Conversion Efficiency

Layered pseudo‐2D perovskites are new and emerging candidates for optoelectronic applications, exhibiting excellent physical properties and very high stability compared to bulk perovskite structures. Herein, two synthesized inorganic layered perovskites with Ruddlesden–Popper phase Cs2XI2Cl2 (X = Pb, Sn) are investigated. The optoelectronic properties of these structures are calculated using density‐functional theory (DFT). In addition, single junction solar cells and a Cs2PbI2Cl2/Cs2SnI2Cl2 tandem cell, are investigated using the finite‐difference time‐domain method and drift‐diffusion model. The optimal absorption coefficient and suitable bandgap for solar cells are indicated by the results obtained from DFT. Based on the deformation potential theory, the ultrahigh charge‐carrier mobility of 104 order are predicted for these structures, which is much higher than the mobility of 3D known organic perovskites. Remarkable power conversion efficiencies of 24.09% and 21.94% for Cs2SnI2Cl2 and Cs2PbI2Cl2 solar cells, respectively, are shown in the calculated results, which are among highest reported efficiencies for layered perovskite solar cells. Also, the simulated tandem cell achieves a high open‐circuit voltage (Voc) of 1.68 V, which is higher than the Voc of single‐junction cells. The high potential of inorganic layered perovskites in optoelectronic devices with excellent efficiency and long‐term stability is implied by the obtained results. Layered pseudo‐2D perovskites are new and emerging candidates for optoelectronic applications. Two synthesized inorganic layered perovskites with Ruddlesden–Popper phase Cs2XI2Cl2 (X = Pb, Sn) are investigated. Single‐junction solar cells and a Cs2PbI2Cl2/Cs2SnI2Cl2 tandem cell are investigated using the density functional theory and finite‐difference time‐domain method.