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 10(4) 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 (V-oc) of 1.68 V, which is higher than the V-oc 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.