Study on the thermal stability of Ga-doped ZnO thin film: A transparent conductive layer for dye-sensitized TiO2 nanoparticles based solar cells

Abstract

Generally, optoelectronic devices are fabricated at a high temperature. So the stability of properties for transparent conductive oxide (TCO) films at such a high temperature must be excellent. In the paper, we investigated the thermal stability of Ga-doped ZnO (GZO) transparent conductive films which were heated in air at a high temperature up to 500°C for 30min. After heating in air at 500°C for 30min, the lowest sheet resistance value for the GZO film grown at 300°C increased from 5.5Ω/sq to 8.3Ω/sq, which is lower than 10Ω/sq. The average transmittance in the visible light of all the GZO films is over 90%, and the highest transmittance is as high as 96%, which is not influenced by heating. However, the transmittance in the near-infrared (NIR) region for the GZO film grown at 350°C increases significantly after heating. And the grain size of the GZO film grown at 350°C after annealing at 500°C for 30min is the biggest. Then dye-sensitized TiO2 NPs based solar cells were fabricated on the GZO film grown at 350°C (which exhibits the highest transmittance in NIR region after heating at 500°C for 30min) and 300°C (which exhibits the lowest sheet resistance after heating at 500°C for 30min). The dye-sensitized solar cell (DSSC) fabricated on the GZO film grown at 350°C exhibits superior conversion efficiency. Therefore, transparent conductive glass applying in DSSCs must have a low sheet resistance, a high transmittance in the ultraviolet–visible–infrared region and an excellent surface microstructure.