| Popis: |
This chapter has taken a critical review of doped metal oxide thin films with specific emphasis on ZnO. A general overview of ZnO is concisely presented with highlights of its advantages and drawbacks. The basic drawbacks were identified as low electrical conductivity and low spectra absorption due to wide bandgap of ZnO. Doping with Al and In and also dye-sensitization of the photoelectrode were proposed as key techniques to enhance the electrical conductivity and the spectra absorption of the ZnO thin films. Chemical synthesis, characterization, and application of AZO and IZO in DSSC and non-dye–loaded PEC solar cells were reviewed. Two works of Tyona et al. were used to illustrate the chemical synthesis, characterization, and application of AZO and IZO electrodes in DSSC and non-dye–loaded PEC solar cells. The results of their study revealed that there was an effective modification of the bandgap of ZnO upon doping with Al and In, respectively, which gave rise to enhanced electrical conductivity due to increase in charge carrier concentration in the conduction band. Absorption edges were red-shifted up to 540 nm into the visible spectrum, which confirmed improvement in spectra absorption. The study also revealed that with the sensitization of the AZO photoelectrodes with rhodamine 6G dye, the absorption band edges were further red-shifted (650 nm) into the visible spectrum and that confirmed further improvement in spectra absorption of ZnO thin film electrodes. Structural, morphological, and other properties of ZnO such as film thickness and surface wettability were seen to improve upon doping. Analysis of the photovoltaic (PV) activities revealed an optimal photoelectric efficiency of 0.89% for the DSSC of AZO and 2.85% for the IZO electrode. These efficiencies were remarkably higher than the un-doped and non-dye–loaded electrodes. This clearly illustrates the positive impact of doping and dye-sensitization on ZnO. |
