Tuning the optoelectronic properties of AZO thin films for silicon thin film solar cell applications

Abstract

Al-doped ZnO (AZO) thin films are deposited using dc magnetron sputtering and the process conditions are optimized to obtain transparent conducting electrode (TCE) with desirable properties suitable for photovoltaic applications. In the course, the effects of deposition parameters such as growth temperature, deposition time and plasma power density on the structural and optoelectronic properties were investigated using suitable characterization techniques. XRD analysis of the deposited films at different process conditions showed a strong c-axis preferred orientation. The surface roughness of the deposited films was examined using AFM analysis. Elemental analysis was carried out using XPS. The resistivity and sheet resistance of the thin films decreased with increase in temperature, deposition time and power density. The optimized films deposited at 250 °C resulted in electrical resistivity of 6.23 × 10−4 Ωcm, sheet resistance of 9.2 Ω/□ and exhibited an optical transmittance of >85% in the visible range. Figure of merit (FOM) calculations were carried out to analyze the suitability of deposited thin films for thin film amorphous silicon solar cell applications. The photogain of optimized intrinsic a-Si:H layer was in the range of 104, whereas no photogain was observed in doped a-Si:H layers. The thin film solar cell fabricated using the optimized AZO film as TCE exhibited power conversion efficiency of 6.24% when measured at AM 1.5 condition.