Effects of TiO₂: MgO-mixed overlayer on the performance of dye-sensitized solar cells

Photovoltaic performance of dye-sensitized solar cells (DSSCs) with a mixed overlayer composed of TiO₂ and MgO was investigated in detail. The surface of photoelectrode (TiO₂) films was modified with a TiCl4:MgCl2 mixed aqueous solutions with various molar ratios and then calcining to produce the surface-modified TiO₂ photoelectrodes (Ti:Mg-TiO₂/FTO). The highest power conversion efficiency was obtained from DSSC with Ti:Mg(3:7)-TiO₂/FTO, which was prepared from the mixed solution with the molar ratio of 3:7 (TiCl₄:MgCl₂). An enhancement in short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc) of DSSC with Ti:Mg(3:7)-TiO₂/FTO was achieved, compared to those of the reference device with bare TiO₂/FTO. The incorporation of the mixed overlayer on the nanoporous TiO₂ photoelectrode led to an improvement in both the light harvesting efficiency and the electron collection efficiency, thereby increasing the J_sc value. The increase in V_oc value of the device with Ti:Mg(3:7)-TiO₂/FTO was due to the reduced charge recombination between photo-injected electrons and I-3 ions.