Reactive plasma deposition of high quality single phase CuO thin films suitable for metal oxide solar cells

Abstract

Copper oxides are of great potential as active optical absorbing materials for low-cost solar cells based on sustainable and green materials resources. In this work, CuO thin films are deposited at room temperature by reactive sputtering deposition using a novel high target utilization system (HiTUS). The films were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) analysis, scanning electron microscopy, atomic force microscopy, UV–vis-near infrared absorption spectroscopy, and Hall measurement. The results showed that the deposition rate, phase structures, optical, and electrical properties of copper oxide films were strongly dependent on the sputtering power and the oxygen flow rate. The as-deposited films were characteristically polycrystalline, without evident preference in crystal orientations. This led to highly compact films without the formation of through-thickness columnar grain boundaries typical to conventional reactive magnetron sputtering deposited films. Optical absorption spectroscopy showed that all the CuO films from this work exhibited an indirect optical bandgap about 1.5 eV, without evident effect from the oxygen flow rates. Hall measurement revealed that the CuO films were of p type conductivity, with their hole concentration being readily tunable in a wide range of 1017–1022 cm−3. The ability for refined tuning of the concentration of charged carriers (holes) is critical in realizing the great potential in engineering delivery of CuO photovoltaic (PV) cells with high efficiency.