Preparation of highly transparent conductive aluminum-doped zinc oxide thin films using a low-temperature aqueous solution process for thin-film solar cells applications

In this work, we developed a facile route to fabricate highly transparent conductive AZO thin films by using an aqueous solution process followed by an ultraviolet (UV) exposure technique at an annealing temperature as low as 200 °C, where the aluminum citrate complex was used as the Al doping source. Various of deposition parameters in the AZO thin films fabrication process were studied and optimized. The mechanisms on UV exposure and heat treatment to the conductivity improvement and conductivity stability of the AZO films were analysed. Results showed that the AZO thin films under the best parameters conditions demonstrated an optical transmittance higher than 85% in the visible spectra region and a lowest electrical resistivity of 4.8 × 10−3 Ω cm, while exhibited densely oriented columnar grains and uniform surface morphology as well as uniform composition distribution. The UV exposure could remove carbon species from the surface of the AZO thin films to reduce oxygen-related defects and release free carriers at the boundaries and interfaces, thereby improving the conductivity of the AZO thin films. The simultaneous treatment of the AZO thin film by ultraviolet exposure and heat treatment could remove carbon species at a deeper thickness, thereby improving the conductive stability of the AZO thin films. Kesterite Cu2ZnSnS4 thin film solar cells incorporating the optimal AZO thin films as top electrodes demonstrated a best power conversion efficiency (PCE) of 7.15%, which was comparable to the PCE value obtained by using the sputtering deposited AZO thin films as top electrodes.