Effect of Radio Frequency Power on the Properties of Al-Doped ZnO (AZO) Thin Films and Their Application to Cu2ZnSn(S,Se)(4) Thin-Film Solar Cells

Abstract

Cu2ZnSn(S,Se)(4) (CZTSSe) has emerged as an attractive candidate to replace CdTe, CIGS, and silicon-based thin-film solar cells (TFSCs). In the present study, the Al-doped ZnO (AZO) thin films that serve as a window layer in CZTSSe TFSCs were optimized to improve the device efficiency. AZO thin films were deposited on a soda lime glass (SLG) substrate using radio frequency (RF) magnetron sputtering with the varying of the RF sputtering power during the deposition. The influence of different RF-power values on the structural, optical, and electrical properties of the AZO thin films, as well as the CZTSSe TFSC efficiency, were investigated. All of the deposited thin films showed a uniform microstructure with a transmittance of more than 90% in the visible region, although they possess comparable bandgap and resistivity differences. Especially, the AZO thin films that were deposited at 50 and 70 W showed high optical bandgap energies of similar to 3.67 eV, with a transmittance of similar to 90% in the visible region. Alternatively, the AZO thin films that were deposited at 50 W showed improved electrical properties with the lowest resistivity of 4.36 x 10(-4) Omega cm, a higher carrier concentration of 5.95 x 10(20) cm(-3), a high mobility of 24.06 cm(2)v(-1)s(-1), and a lower sheet resistance of 6.4 Omega/SQ. This led to the enhanced device efficiency of the CZTSSe TFSCs with the 50-W-deposited AZO window layer owing to its outstanding optoelectronic properties. Specifically, the improved open-circuit voltage (V-OC) resulted in a high power conversion efficiency (PCE) of 5.53% for the CZTSSe TFSCs. These results signify the effectiveness of AZO as a highly promising TCO for the TFSC application.