Fabrication and characterization of sputtered Mg and F co-doped ZnO thin films with different substrate temperature for silicon thin-film solar cell applications

Abstract

Transparent conducting oxide thin films have been extensively studied for various optoelectronic devices. In this paper, we investigated the influence of substrate temperature on structure, morphology, electrical and optical properties of Mg and F co-doped ZnO (MFZO) thin films. The MFZO films were deposited on glass substrates by radio frequency magnetron sputtering at a temperature ranging from room temperature to 200 °C. Experimental results indicate that small amounts of Mg (3 at%) and F (6 at%) co-doping does not change the (002) oriented hexagonal wurtzite structure of ZnO, but it can improve the crystallinity and optoelectronic properties by increasing the substrate temperature. For all MFZO films, the average transmittance in the visible region exceeds 91%. As the substrate temperature rises to 200 °C, the electrical resistivity of the film drops to 1.18 × 10−3 Ω cm. The high figure of merit (FOM) of the film deposited at 200 °C, 1.36 × 10−2 Ω−1 or 2.96 × 104 Ω−1 cm−1, makes it a transparent conductor of choice for photovoltaic applications. By etching with a dilute HCl solution, the surface morphology of the as-deposited MFZO film was modified to a crater-like texture, resulting in a significant increase in the average haze in the visible region from 4.5% to 52.3%. By employing the developed high-FOM and high-haze MFZO film as the front electrode of a-Si:H thin-film solar cells, a 30% increase in conversion efficiency was achieved under AM 1.5 G illumination.