Synthesis and Optimization of Planar Perovskite Solar Cells Using TiO2/SnO2, TiO2/WO3 and SnO2/WO3 Electron Transport Bilayer Structures

 In perovskite solar cells (PSCs), effective electron extraction and reduction of electron-hole pair recombination at the electron transport layer (ETL)/perovskite interface is essential for obtaining higher performance. In this research, the presence effect of a metal oxide ultra-thin layer (< 10 nm thick) on the major ETL (≈ 50 nm thick) in improving the photovoltaic performance of the cell was investigated. For this purpose, a complete set of bilayer structures for the three common ETL metal oxide materials TiO2, SnO2 and WO3, were provided using the accurate and reproducible radio-frequency (RF) sputtering deposition method, and their performance as ETL in the cell was compared. Structural and electrical characterizations of different cells and ETLs were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-vis spectroscopy, Mott-Schottky analysis and J-V diagrams. The use of TiO2/SnO2-UTL, TiO2/WO3-UTL and SnO2/WO3-UTL bilayer structures has been shown to significantly increase cell efficiency by creating more efficient energy band alignment. On the other hand, using their inverted bilayer structures, SnO2/TiO2-UTL, WO3/TiO2-UTL, and WO3/SnO2-UTL, resulted in reduced cell efficiency. The results suggest a simple and promising approach to designe more efficient photovoltaic devices with improved performance.