Research On Spectroelectrochemical Properties Of Cu-doped And Ag-doped TiO₂ And Assembly Of DSSCs

Energy and environment are crucial problems toward global economic development and political stability. Finding and applying green and clean energy instead of fossil energy is a key route to solve these problems. The photovoltatic application of solar is the main form of energy development in the future, especially dye-sensitized solar cells. Titanium dioxide(Ti O2) is considered very close to an ideal semiconductor for photoanode because of its high stability, inexpensive and non-toxic. In this paper, we aimed to modify Ti O2 with transition metal Cu and Ag. Cu-doped Ti O2 and Ag-doped Ti O2 powders were synthesized via a simple sol-hydrothermal route, the obtained powders were investigated by XRD, SEM, XPS, and UV-Vis-NIR. The result presented that there were less influences on the crystal form of Ti O2 and particle size was decreased due to the presence of Cu-O-Ti and Ag-O-Ti, which inhibited the growth of crystal grains. Meanwhile, the absorption band edge of Cu-doped Ti O2 shifted toward long wavelength, which was good for absorbing sunlight. For Ag-doped Ti O2, the absorption band edge shifted toward long wavelength slightly owing to the difference of optical and electrical properties with Cu.Then synthetic powders were used as photoanode materials and we assembled DSSCs to test. The result showed that η increased first and then decreased with the dopant increased. The reason for this phenomenon is that doping with a moderate amount improves the valid utilization percentage of sunlight so that we got better performance of DSSC. Nevertheless, too high doping level will lead into more defects serving as carrier trapping centers, which does harm for short circuit current density(Jsc). For the DSSC of Cu-doped Ti O2, we got the highest η of 6.12% when doping content was 1.0 at.%. For the DSSC of Ag-doped Ti O2, we got the highest η of 7.34% when doping content was 1.2 at.%. The higher performance comparing with Cu-doped Ti O2 was because of the better electroconductibility and easy to reduce carrier trapping centers. The Ti Cl4 post-treatment on nanocrystalline Ti O2 films as electrodes in dye-sensitized solar cells can increase the specific surface area of Ti O2 films which is good for adsorption of dye and to improve the photocurrent. So we investigated the properties of Ti Cl4 post-treatment doped Ti O2 DSSC. The result showed that Ti Cl4 post-treatment didn’t change the law causing by doping and improve the conversion efficiency effectively.Then a variable temperature spectroelectrochemistry was applied to prove the change by measuring the conduction band energy of Ti O2 and doped Ti O2 working electrodes, the results showed that the bottom of conduction band with doping product was decreased. The lower conduction band positions of Cu-doped Ti O2 and Ag-doped Ti O2 made the driving force of electrons increase and then improved the electron injection efficiency. The consequence gives a powerful evidence for the nice performance.