Influences of deposition and post-annealing temperatures on properties of TiO2 blocking layer prepared by spray pyrolysis for solid-state dye-sensitized solar cells

Influences of the temperature (Ts) for spray pyrolysis deposition of TiO2blocking layer (BL) using titanium diisopropoxide bis(acetylacetonate) (TAA) as a precursor and the temperature (Tp) for post-annealing of the BL films on the resulting BL film morphology and photovoltaic performance of solid-state dye-sensitized solar cells (SDSC) are investigated. A Tsranging from 300 to 400 degree C is found preferable for the formation of BL films with smooth surface and dense grain packing. A Tslower than 300 degree C results in insufficient decomposition of the TAA precursor and is unable to form smooth BL films, while a Tsover 400 degree C leads to loosely packed grain in BL films. Power conversion efficiency (PCE) of ~4.0% is obtained for SDSC devices with BL films prepared at a Tsin the range of 300-450 degree C. High temperature post-annealing (Tp=500-550 degree C) of the BL films prepared at a low Ts, such as 300 degree C, can improve the PCE up to 4.6%. The improvements are considered due to the higher purity, increased crystallinity, and retained high grain packing density of the post-annealed BL films, which facilitate charge transport and suppress charge recombination.