DFT and AMPS-1D simulation analysis of all-perovskite solar cells based on CsPbI3/FAPbI3 bilayer structure

Very recently, perovskite solar cells (PSCs) have been proposed with both new device structure and materials to replace the conventional Methyl Ammonium-based structures in order to develop cells with higher operational stability. All-perovskite solar cells are the most emerging class of organic-inorganic PSCs which combine the photogeneration and absorption capability of two different perovskite materials to ensure both photo conversion performance and device operational stability. This simulation work aims to develop a systematic investigation of an all-perovskite solar cell structure made of CsPbI3/FAPbI3 heterojunctions using wxAMPS-1D platform supported with Density Functional Theory (DFT) simulations to analyze the band structure of both CsPbI3 and FAPbI3 materials. The quantum efficiency, device characteristics, and degradation trend have been optimized against the thickness of perovskite layers. The optimum thicknesses are obtained to be 200 nm for CsPbI3 layer at an assumed thickness range of∼300 nm for FAPbI3 as stated in different literature, 30 nm for TiO2 electron transporting layer, and 80 nm for Spiro-OMeTAD hole transporting layer. The optimized CsPbI3/FAPbI3 bilayer all-perovskite solar cell results in 19.94% efficiency (PCE), short-circuit current density (Jsc = 24.5 mA/cm2), and open circuit voltage (Voc = 1.1 V), and a fill factor (FF) = 74%. The bilayer structure (CsPbI3/FAPbI3) shows 20% improvement in external quantum efficiency (in visible range), compared to the cell made of single CsPbI3 or FAPbI3 layer. Moreover, the degradation analysis shows that increasing the mid-gap defect density (in both layers) up to 1015 cm−3 was detrimental to device performance.