It is well known that electron mobility of ZnO is much
higher than that of TiO2, while the conduction band edge of
both materials is approximate at the same level. In this study,
ZnO and Ga-doped ZnO fabricated by sol-gel process were
inserted between FTO and nanoparticle TiO2 layer, as shown
in Fig. 4. However, the reported photocurrent conversion
efficiency of ZnO DSSCs is far less than that of TiO2 due to
the poor dye absorption of ZnO.