Effect of Li-doped TiO2 compact layers for dye sensitized solar cells

Both TiO2 compact layer (d-TiO2) and Li-doped TiO2 compact layer (d-Li-TiO2) were deposited between nano-TiO2 and transparent conductive oxide (TCO) for dye sensitized solar cells (DSSC) by the technique of pulsed laser deposition (PLD). XRD pattern shows the compact layers are crystallized in anatase structure. Compared with FTO-based DSSC without compact layer, the open voltage decay measurement shows the novel structure can slow the decay of the open circuit voltage, indicating an effective suppression of back electrons transfer from TCO to the electrolyte by the dense buffer layers. In addition, the interface resistance between the nano-TiO2 and the TCO falls down due to the reduced energy band-gap of Li-doped TiO2, which makes it easier to transfer the generated electrons from conducting band of nano-TiO2 to TCO surface, leading an enlarged short current from 4.2 mA/cm(2) of FTO-based to 4.8 mA/cm(2) for that with d-TiO2 and 6.1 mA/cm(2) for d-Li-TiO2, respectively. Thus, the photovoltaic energy conversion efficiency of DSSC based on the Li-doped TiO2 compact layer enhances as much as 42% compared with that FTO-based DSSC without TiO2 compact layer.