Increased photovoltaic performance by the optimized TiCl₄and AlCl₃ surface treatment in dye-sensitized solar cells

The surface of TiO₂ photoelectrodes coated on F-doped SnO₂ (FTO) was modified by soaking it in a TiCl₄:AlCl₃ mixed aqueous solution with various molar ratios, and then calcining to produce the TiCl₄:AlCl₃-treated TiO₂ photoelectrode (Ti:Al-TiO₂/FTO). The highest power conversion efficiency (PCE) was obtained from dye-sensitized solar cells (DSSC) with Ti:Al(5:5)-TiO₂/FTO, which was prepared from the mixed solution with the molar ratio of 5:5 (TiCl₄:AlCl₃). PCE of DSSC with Ti:Al (5:5)-TiO₂/FTO was improved by ca. 19.6%, compared to that of the reference device with Ti:Al (10:0)-TiO₂/FTO (i.e., TiO₂-coated TiO₂/FTO) due to an enhancement in both short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc). A series of measurements such as UV-visible absorption, electrochemical impedance, open circuit voltage decay and dark current revealed that the increase in J_sc was attributed to the improvement of electron collection efficiency by a prolonged electron lifetime, and the suppression of the charge recombination between injected electrons and I-3 ions was found to increase the Voc value of the device with Ti:Al(5:5)-TiO₂/FTO.