Deposition of large area, directly textured, ZnO:Al films by reactive-environment, hollow cathode sputtering

Abstract

Aluminum-doped zinc oxide (ZnO:Al) is a promising transparent conducting oxide (TCO) for the second generation, thin film based solar cells. Moderately large area, directly textured ZnO:Al films were successfully deposited by reactive-environment, hollow cathode sputtering (RE-HCS) using metal targets. The morphology, structural, electrical, and optical properties of the films have been investigated and comparisons are made with the properties of commercially available textured SnO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> :F. Higher haze and reduced absorption could be obtained with the textured ZnO:Al films. Besides the textured surface, these films (∼1030nm thick) also have a low sheet resistance of 2.8 ohms/square. Hall effect measurements on these films yielded a record high mobility of 49.5 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s and carrier concentration of 4.42 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> . The use of these textured ZnO:Al films as a TCO for single junction a-Si cells resulted in increased V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> , J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> , and FF. The novel deposition method of RE-HCS provides a possible and promising pathway to a relatively low cost, large area production process for a textured ZnO TCO for thin-film PV manufacturing.