Enhanced performance of planar perovskite solar cells using TiO2/SnO2 and TiO2/WO3 bilayer structures: Roles of the interfacial layers

In planar perovskite solar cells (PSCs), engineering the extraction and recombination of electron-hole pairs by modification of the electron transport layer (ETL)/perovskite interface is very vital for obtaining high performance. The main idea here is to improve properties of the TiO2/perovskite interface by inserting an ultra-thin layer (UTL) of WO3 or SnO2 with the thickness of less than 10 nm by RF magnetron sputtering method. The structural and electrical characteristics of the samples were tested by XRD, AFM, FE-SEM, Mott-Schottky analysis, UV-Vis spectroscopy, J-V characterization and electrochemical impedance spectroscopy (EIS). It was found that the bilayer structured ETLs exhibit advantages of high electron extraction and low interfacial recombination together mainly based on a more effective energy level alignment. The best performance here belongs to the cell with TiO2/SnO2 bilayer by which an improved efficiency exceeding 12% was achieved for the planar PSCs. The role of SnO2 and WO3 UTLs was also modeled using SCAPS-1D software. This simulation supported the experimental results and was used to interpret the photovoltaic behaviors of the fabricated devices based on defect characteristics. The present work proposes a simple and promising method to make photovoltaic devices with desirable charge transport and recombination properties.