p-type oxide semiconductors as hole collectors in dye-sensitized solid-state solar cells
Oxide semiconductors with p-type conductivity were found to be good candidates to be used as hole collectors in dye sensitized solid-state solar cells (DSSC). In this paper, a delofossite p-type CuAlO2 semiconductor was synthesized by a hydrothermal method and its properties were investigated as a hole collector in DSSC. The valence band (VB) and conduction band (CB) positions of CuAlO2 were appropriate to be used as the hole conductor in DSSC. Solar cells constructed with TiO2/Ru dye/CuAlO2 deliver Isc = 0.08 mA cm−2 and Voc = 525 mV. The particle size of CuAlO2 prepared by the hydrothermal method was ~300–500 nm and the large CuAlO2 particle penetrates weakly into the pores of a nanocrystalline matrix resulting in the weak interaction of the dye and hole collector, which was found to be one of the reasons for the poor solar cell performance of the solar cell constructed with CuAlO2 as the hole collector. Bigger particle size and poor p-type conductivity are found to be the major limiting factors of CuAlO2 as a hole collector. The solar cell performances of electrodes constructed with TiO2/Ru dye/NiO are also discussed.