All-oxide solar cells based on electrodeposited Cu2O absorber and atomic layer deposited ZnMgO on precious-metal-free electrode

Abstract

All-oxide solar cells based on electrodeposited p-type Cu2O absorber and atomic layer deposited n-type ZnMgO are investigated. The introduced solar cell architecture is free of precious metals that are usually employed as electrodes in Cu2O solar cells and is composed almost exclusively of oxide layers. Firstly, a detailed investigation is made on the potentiostatic electrodeposition of the absorber layer on the sputtered, highly conductive and reflective Cr/ITO (ITO: tin-doped indium oxide) electrode. The focus is set on adjusting the deposition parameters to obtain Cu2O layers, which are void-free and with large grains. A multi-textured film is obtained with prominent (111), (200) and (220) reflections. The absorber has a bandgap of 1.93eV and a rough, antireflective surface. Next, the n-type ZnMgO layer has been investigated and a linear relation of the optical bandgap (3.2–3.9eV) versus Mg content was found. The valence band maximum levels have been extracted from X-Ray photoelectron spectroscopy and the band alignment of the Cu2O/ZnMgO was evaluated. Solar cells employing ZnMgO films with ~10at% Mg show best photovoltaic performance, whereas for larger Mg contents a dramatic decrease of the performance takes place, presumably due to excessive, deep-level defects, leading to tunnel recombination. Best cells show short circuit current density of 6.8mA/cm2, open circuit voltage of 550mV, fill factor of 45% and power conversion efficiency of 1.67%.