Newly designed dye-sensitized solar cells fabricated with double-layered TiO2 (bottom layer)/Bx–TiO2 (top layer) combined electrodes for improved photocurrent

Abstract

An unusual double-layered TiO2 (bottom layer)/Bx–TiO2 (top layer) combined electrode array was investigated to improve the photocurrent in dye-sensitized solar cells (DSSCs). A positive semiconductor, Bx–TiO2, with nanometer-sized B (1.0, 5.0, and 10.0mol%)-incorporated TiO2 prepared using a solvothermal method, was utilized as the working electrode material by coating onto the second level above the TiO2 electrode. The photocurrent and photovoltaic efficiency of the TiO2 (bottom)/Bx–TiO2 (top)-DSSC were 20.5% and 17.3% greater, respectively, than that of the double-layers of anatase TiO2–DSSC in the photocurrent–voltage (I–V) curve of the optimal electrode. This result was attributed to their energy levels of reduction (LUMO)/oxidation (HOMO) as determined by cyclic voltammetry (CV). As the LUMO level of Bx–TiO2 was located at a slightly higher level than that of pure anatase TiO2, the electrons donated from the dye were easily transferred to the surface of the TiO2 electrode without electron loss. Moreover, the recombination was also much slower in the TiO2 (bottom)/Bx–TiO2 (top)-based DSSCs than in the double-layered pure TiO2 DSSC.