Synthesis of ZnO:Al Transparent Conductive Thin Films Using Sol-gel Method

Tin-doped indium oxide (ITO) deposited by vacuum process with excellent optical and electrical properties have been generally used as transparent conductive oxide thin films. In view of high cost and difficulty in recycles for vacuum process, zinc oxide films synthesized by wet chemical process are therefore regarded as a more suitable candidate to replace ITO. In this work, sol-gel method was used to synthesize transparent aluminum-doped zinc oxide (ZnO:Al, AZO) with 450 nm thickness for large scale production of CIGS solar cell. The experimental parameters included different solvents, the propylene glycol methyl ether (PGME) to replace the usually used solvent ethylene glycol monomethyl ether (EGME) which is toxic, the amount of Al dopant (ranged from 0 to 2 at%), and various annealing temperatures. The structure, electrical and optical properties of AZO thin films are investigated by a field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), four-point probe (FPP) and ultraviolet visible light spectroscope (UV-VIS) etc. The experimental results showed that the AZO films were wurtzite crystalline with c-axis preferred orientation and had > 85% transmittance and lower electrical resistivity after annealed in N2 atmosphere. The optimum AZO samples had low electrical resistivity of 1.94¥10-2 Ω-cm, which were synthesized with PGME solvent, 1 at% Al-doping and annealed at 600 °C in N2 atmosphere and 500°C in 95 N2/5 H2 atmosphere for one hour, separately.