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 TiO2 blocking 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 Ts ranging from 300 to 400 °C is found preferable for the formation of BL films with smooth surface and dense grain packing. A Ts lower than 300 °C results in insufficient decomposition of the TAA precursor and is unable to form smooth BL films, while a Ts over 400 °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 Ts in the range of 300–450 °C. High temperature post-annealing (Tp = 500–550 °C) of the BL films prepared at a low Ts, such as 300 °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.