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

s This study investigates the TiO x compact layers deposited by mid-frequency magnetron sputtering of Ti target under a gaseous atmosphere of Ar/O 2 . X-ray photoelectron spectroscopy suggests that the compact layer consists of 55% Ti 3+ and 45% Ti 4+ . Current–voltage measurements reveal that the TiO x 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 TiO x 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 TiO x film suppresses the charge recombination more effectively, leading to longer electron lifetime of the solar cells. Nevertheless, higher resistance of the thicker TiO x film decreases its electron transport ability, thereby leading to lower PCE . Besides, compared to liquid-state solar cells, solid-state solar cells require thicker TiO x compact layer to block the electron loss and show larger increase of PCE (highest 27% enhancement in liquid-state solar cells with 85   nm TiO x layer), which corresponds to the much faster charge recombination and ~15 times lower electron-carrier lifetime in solid-state solar cell.