Investigation of thickness dependent efficiency of CsPbX3 (X = I, Br) absorber layer for perovskite solar cells

The drawbacks of solar cells consisting of hybrid organic-inorganic lead halide perovskites led to the development of solar cells containing completely inorganic perovskites. Therefore, here we have carried out detailed density functional theory (DFT) based investigation of cubic phase CsPbX3 (X = I, Br). Absence of imaginary frequencies in phonon dispersion curves and negative cohesive energies of the perovskites depicts stability of our crystal structures. From electronic properties of CsPbI3 and CsPbBr3 we have deduced that the major contributions in their valence band region is due to I-5p and Br-4p orbitals, respectively. The static dielectric constant of CsPbI3 is greater than CsPbBr3 which shows that it consists of low carrier recombination rate. Red shift has also been observed in absorption coefficient plot while going from Br -> I in CsPbX3. The thickness of absorber layer present in perovskite solar cells (PSCs) directly influences its efficiency and stability. Therefore, here we have used a detailed framework i.e., spectroscopic limited maximum efficiency (SLME) to predict solar cell parameters of perovskites absorber layer as a function of their thicknesses. Using SLME approach which is thickness dependent it has been predicted that at thicknesses above 2.56 mu m and 1.39 mu m of absorber layers CsPbI3 and CsPbBr3, respectively, their efficiencies obtained using SLME approach are higher compared to that obtained using Shockley-Queisser (SQ) limit. The efficiencies of CsPbI3 and CsPbBr3 absorber layers calculated using SLME approach at absorber thickness of 20 mu m are obtained around 30.41% and 24.53%, respectively.