The effect of built-in field on the surface photovoltage(SPV) response of ZnO nanoparticles was investigated by means of surface photovoltage spectroscopy(SPS). From the results of in situ SPS in atmosphere and in vacuum, we suggest that the built-in field should be a main condition for producing SPV response. By comparison of SPS with PL in vacuum as well as in atmosphere, we deduce that by changing the ambience of ZnO, its functional properties can be modulated.
The TiO2 based dye-sensitized solar cells doped with different sizes of ZnO nanorods were fabricated and studied by photoelectrochemical measurements. The results show that the energy conversion efficiency of the dye-sensitized solar cells after the addition of ZnO nanorods(1%, mass fraction) was increased by 6%—20% in comparison with that without ZnO nanorods. The effect of different sizes of ZnO nanorods on the electronic transportation properties was studied in the composite semiconductor film by means of transient photovoltage technology(TPV). The result indicates that the electron diffusing velocity in N3-sensitized TiO2/ZnO film electrode was about 1—3 order of magnitude faster than that in TiO2 electrode. The experimental results indicate that the TiO2/ZnO electrode can improve the electron transport, decrease the recombination, enhance Voc, and increase efficiency of energy conversion.
Transient photovoltage(PV) technique was applied to investigate the separation and the transport mechanism of the photo-induced charge carriers on nano-TiO_ 2 film electrode. The positive PV transients were observed whenever the light was incident from the gauze platinum(top illumination) or the ITO electrode(bottom illumination). This implies that the photo-induced electrons always accumulate near the ITO. Simultaneously, it is found that under the singe pulse illumination, PV transient at bottom illumination needs a shorter time to reach its maximum than that at top illumination. This indicates that the photo-induced carriers are separated faster on TiO_ 2/ITO interface than that in the bulk of the TiO_ 2 film. These demonstrate the existence of the contact potential on the TiO_ 2/ITO interface, with the downward band bending from the TiO_ 2 to ITO, which may cause the excess carriers to be separated by drift. Under the repeated pulses illumination, the PV transients at top illumination remained unchanged, while those at bottom illumination changed significantly. This results from the trapping of the excess electrons on the TiO_ 2/ITO interface.
