Effect of hydrogen doping on the properties of Al and F co-doped ZnO films for thin film silicon solar cell applications

• H2 doping improves optoelectronic properties of Al, F co-doped ZnO (AFZO) films.
• Resistivity of AFZO films decreases to 4.4 × 10− 4 Ω-cm with the 3% H2/(Ar + H2) ratio.
• AFZO films show high average visible transmittances of above 92%.
• Efficiency of a-Si thin film solar cells is improved by AFZO:H as front electrode.

Aluminum and fluorine co-doped zinc oxide (AFZO) thin films were prepared in Ar + H2 atmospheres by rf magnetron sputtering at room temperature. The structural, electrical, and optical properties of the prepared films were investigated using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Hall-effect measurement, X-ray photoelectron spectroscopy, and ultraviolet–visible spectrometry, and their dependence on deposition atmosphere (i.e. H2 / (H2 + Ar) ratio) was studied. The resulting films showed a (0 0 2) diffraction peak, indicating a typical wurtzite structure, and the optimal film crystallinity was obtained with the H2 / (H2 + Ar) ratio of 3%. The electrical resistivity of AFZO films decreased to 9.16 × 10− 4 Ω-cm, which was lower than ZnO:Al and ZnO:F films due to double doping effect of Al and F. The resistivity further decreased to below 5 × 10− 4 Ω-cm for the AFZO film with the H2 / (H2 + Ar) ratio of 3%–5%. All the films regardless of hydrogen content displayed high transmittances (> 92%) in the visible wavelength range. Applying the developed AFZO films as front transparent electrodes, amorphous Si thin film solar cells were fabricated and the open-circuit voltage, fill factor, and efficiency of the cell with the hydrogenated AFZO film were improved in contrast to those without the hydrogenated film.