In Situ Growth Of Doping TiO₂ Thin Film Electrod And Photoelectric Performance

The TiO₂ film electrode is the important part of the dye-sensitized solar cells. The development of simple production process and TiO₂ film with a strong adhesion will promote the practical application. In this paper, the TiO₂ thin film electrode with large area is in situ grown on titanium by micro-plasma oxidation.The effect of electrolyte, current density, voltage, concentration of electrolyte, time and sensitization process on photoelectric performance of thin TiO₂ film electrode is studied. The TiO₂ film electrode grown in situ has been prepared through optimizing process parameters. TiO₂ film electrode has optimum photoelectric performance in (NH4)2SO4 electrolyte when TiO₂ film is prepared under the current density of 14 A/dm2, voltage of 245 V, electrolyte concentration of 0.5 mol/L, the reaction time of 10min, sensitizing temperature for 25℃and dye concentration of 0.2 mmol/L. The open circuit voltage, short circuit current, fill factor and photoelectric transfer efficiency is 652 mV, 149μA/cm2, 0.39 and 0.095% respectivly.The effect of the N, S, Nd alone doping and N and Nd co-doping on optoelectric properties of TiO₂ film electrodes in-situ grown is studied. The results show that N, S, Nd alone doping and N and Nd co-doping can significantly increase photoelectric performance of the TiO₂ thin film electrode. Also, the photoelectric performance of the alone doped TiO₂ film electrode is superior to that of the co-doped TiO₂ film electrode and N-doped TiO₂ film electrode shows the best photoelectric performance. The open circuit voltage, short circuit current, fill factor and photoelectric conversion efficiency reaches 701 mV, 165μA/cm2, 0.42 and 0.121% respectivly.The morphology, cell parameters, grain size, absorption spectrometry and internal resistance of the TiO₂ film before and after the doping ions were analyzed by using SEM, XRD, XPS, UV-vis DRS and EIS. The results show that the film is composed of rutile TiO₂ phase and small amount of Ti and there are a lot of uniform porous on the surface of TiO₂ film. Doping ions into TiO₂ can expand the cell volume and reduces the grain size, the band gap and the internal resistance. Comparing these samples, the bandgap of Nd-doped TiO₂ film is minimum and the internal impedance of N-doped TiO₂ is minimum.The photo-induced electronic reaction and the dynamic behavior of photoelectrons in TiO₂ interface are researched. The results show that the photo-induced electron transfer and the rapid photo-electronic injection into TiO₂ film can be achieved successfully. Smaller crystal grain size and internal impedance can reduce the annihilation of the photoelectron at the TiO₂ interface.The band structure of N and Nd-doped TiO₂ electrode is calculated by the First-principles. The results show that energy bands of impurities exist in N-doped and Nd-doped TiO₂ band structure, which narrows the band gap of TiO₂ band gap. The results are in good agreement with experimental data. So, it can be conclueded that doped modification can adjust the energy band structure of TiO₂ film grow in situ, and improve the photoelectric performance of TiO₂ film.The photoelectric conversion behavior of the doping TiO₂ thin film grown in situ is discussed. It is found that the grain size, the internal resistance and the band gap affect the optoelectronic properties of TiO₂ film cooperatively. The good match among the three factors can bring the higher photoelectrode performance of thin TiO₂ film electrodes grown in situ.