Sputtered TiOx thin film as compact layer for solid-state dye sensitized solar cells

This study investigates the TiOx compact layers deposited by mid-frequency magnetron sputtering of Ti target under a gaseous atmosphere of Ar/O2. X-ray photoelectron spectroscopy suggests that the compact layer consists of 55% Ti3+ and 45% Ti4+. Current-voltage measurements reveal that the TiOx film effectively impedes the leakage of current at the FTO/hole transporting material (HTM) interface. Current-voltage curves, electrochemical impedance spectroscopy and open-circuit voltage decay are used to evaluate the function of TiOx compact layer in the solid-state solar cells. Results show that the best cell performance is observed in the cell with optimum compact layer thickness of 85 nm, which shows 814% increase in the power conversion efficiency (PCE) when compared with the bare cell. Thicker TiOx film suppresses the charge recombination more effectively, leading to longer electron lifetime of the solar cells. Nevertheless, higher resistance of the thicker TiOx film decreases its electron transport ability, thereby leading to lower PCE. Besides, compared to liquid-state solar cells, solid-state solar cells require thicker TiOx compact layer to block the electron loss and show larger increase of PCE (highest 27% enhancement in liquid-state solar cells with 85 nm TiOx layer), which corresponds to the much faster charge recombination and ~15 times lower electron-carrier lifetime in solid-state solar cell.