Influences of Sr-incorporated TiO₂ layer on the photovoltaic properties of dye-sensitized solar cells

Effects of a mixed overlayer composed of TiO₂ and TiSrO3 on the performance of dye-sensitized solar cells (DSSCs) were investigated. The surface of TiO₂ photoelectrode formed on F-doped SnO2 (FTO) was modified by soaking it in a TiCl₄:SrCl₂ mixed aqueous solution with various molar ratios and then calcining to produce the TiCl₄:SrCl₂-treated TiO₂ photoelectrode (Ti:Sr-TiO₂/FTO). The highest power conversion efficiency (PCE) was obtained from DSSC with Ti:Sr(7:3)-TiO₂/FTO, which was prepared from the mixed solution with the molar ratio of 7:3 (TiCl₄:SrCl₂). An enhancement in short-circuit photocurrent (Jsc) and open-circuit voltage (Voc) of DSSC with Ti:Sr(7:3)-TiO₂/FTO was achieved, compared to those of the reference device with Ti:Sr(10:0)-TiO₂/FTO (i.e., TiO₂-coated TiO₂/FTO). The incorporation of the mixed overlayer on the nanoporous TiO₂ photoelectorde led to an improvement in the electron collection efficiency by a prolonged electron lifetime, thereby increasing the Jsc value. The increase in Voc value of the device with Ti:Sr(7:3)-TiO₂/FTO was due to the suppression of the charge recombination between injected electrons and I-3 ions.