| Nb doping TiO2 transparent conductive films, which have an excellent photoelectric properties and relatively low cost elements, attract widely attention in TCOs field. However, restricted by the preparation methods, transparent conductive TNO film was still in the stage of research and development at present. In this paper, using sol gel and subsequent annealing method to prove the Nb doping efficiency and effective ionization rate of doped Nb atoms firstly. Then discuss the feasible solutions in improving photovoltaic performance of TNO thin films basing on the doping concentration, crystal morphology and annealing condition. The scheme involved include:increasing Nb doping concentration and introducing oxygen vacancies to improve the concentration of carriers in the TNO film, preparing with columnar crystal morphology of TNO films to improve the mobility and remain favourable transmittance in same time..The specific research results are as follows:Through sol gel and annealing process, Nb atoms have doped in the lattice of TiO2 and replaced the Ti atoms. There is no oxidation phase or other forms containing Nb atoms. The actual Nb doping amount is nearly equal to nominal Nb doping concentration. It proves sol gel method can effectively control the Nb doping concentration. But the effective ionization rate of doping Nb atoms decreases with the increase of the Nb doping concentration.Therefore, choosing an appropriate doping concentration is important to the study of transparent conductive TNO film.With the increase of Nb doping concentration, (101) peak intensity of anatase phase decreases, and the peak position shift to the left, so the spacing of TiO2 increases, but the crystallinity and crystal morphology of samples was gradually get badly. In the same time, the conductivity and visible light transmittance has a tendency to decline. It can be concluded that the doping concentration in 10-15% of the samples with the best photoelectric comprehensive performance.Under the condition of the same concentration, the morphology with columnar crystal is obviously better than the granular sample in crystal properties. Resistivity of the sample of the columnar crystal more than an order of magnitude lower than granular sample, and visible light through performance did not improve, but remain at about 78%. It shows that visible light transmittance rise space is very small in the condition of favourable crystallization properties. And the 10 at.% samples with the columnar crystal has the most excellent electrical performance, which resistivity can be measured as 2.7Ω· cm and transmittance 69%. The result is very close to the best electrical performance of sol gel TNO samples.High vacuum annealing can promote the formation of oxygen vacancies in the TNO films. So it can greatly improve the conductivity of TNO films. Because of the absorption by oxygen vacancy on the photons, the visible light transmittance would drop as oxygen vacancies increase. After annealing in H2+N2 gas mixture, the electrical performance and visible light transmittance is lower than high vacuum condition but higher than N2 annealing condition. After N2 annealing, samples own the best performance of visible light, but the resistivity is highest, and crystal morphology is poorest. It can be concluded that the increase of oxygen vacancy concentration can greatly improve the conductivity but decrease the transmittance of TNO films. |
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