Effect of rapid thermal annealing time on ZnO:F thin films deposited by radio frequency magnetron sputtering for solar cell applications

Transparent conducting films are extensively used in optoelectronic devices. In this work, fluorine-doped zinc oxide (FZO) thin films were deposited from a ZnO:ZnF 2 (3 mol%) target by radio frequency magnetron sputtering. A post-deposition rapid thermal annealing (RTA) was performed in vacuum at 400 °C for 15–120 s. Effect of RTA time on the structural, electrical, and optical properties of FZO thin films was explored. X-ray diffraction patterns showed intense (0 0 2) diffraction peaks at 2 θ ~ 34.4°, corresponding to a hexagonal wurtzite structure. As the RTA time increased from 0 to 30 s, the film resistivity decreased by 36% and reached the lowest value, 7.97 × 10 –4 Ω cm. Obvious absorption edges were observed in the ultraviolet region, and the average transmittance of all films in the visible region exceeded 91%. The corresponding optical bandgap increased from 3.751 to 3.804 eV after the 30 s-RTA process. The figure of merit for evaluating TCO performance increased by 91% to 1.92 × 10 –2 Ω −1 . For solar cell applications, the HCl-etched FZO thin films exhibited a crater-like surface structure and achieved a high average haze of 27.3% in the visible region. By utilizing the developed FZO thin film as the front electrode of the superstrate α-Si:H thin-film solar cell, the conversion efficiency increased by 20% compared with the counterpart without RTA. These results demonstrate that post-deposition RTA is an effective method to enhance the optoelectronic properties of FZO thin films. The developed RTA-treated FZO film is an effective alternative to the transparent electrode of solar cells.