Abstract
We report on the successful growth optimization of an inorganic p-type copper oxide (Cu2O) thin films for various energy applications. First, Cu2O thin films of a typical thickness of 100 nm are deposited on fluorine-doped tin oxide (FTO) coated glass substrates by DC-reactive magnetron sputtering, followed by their in-depth characterization with different techniques, including scanning electron and atomic force microscopies, UV-Vis, X-ray diffraction and photoelectron spectroscopies, to probe their structural, optical, and morphological properties. Surface topology analysis revealed homogeneous, compact, and uniform sputtered deposited films. The as deposited films layers have shown a preferential crystal orientation of (111) and a stoichiometry of CuO, at the surface, which is believed to be mainly due to the oxidization effect of the non-capsulated surface, while a short-duration argon etching (~ 5 s) has revealed the growth of Cu2O films stoichiometry. Finally, during the reactive plasma deposition, films were grown under nitrogen gas flow to improve their hole-mobility, followed by a systematic annealing at various temperatures ranging from 100 to 250 °C to improve their crystalline structure. Hall effect measurement confirmed that the Cu2O thin film are p-type, with extremely high electronic properties, including an electrical conductivity of 2.6 × 102 S/cm, a hole mobility of about 30 cm2/Vs and a charge carrier density around 5 × 1019 cm-3, making them a serious candidate for a hole transport layer in perovskite solar cells.
Highlights
Cuprous oxide (Cu2O) is a well-established p-type material and its conductivity is directly correlated with the oxygen rich or poor layers due to the variation in growth processes [1]
Cu2O films were deposited by direct current (DC) magnetron sputtering (Torr International’s MagSputTM series CRC 600) with a power density of 1.5 W/cm2, using Cu target (99.999% purity), at various temperatures ranging from 100 °C to 250 °C, under oxygen and nitrogen flow, with a background pressure of about 10 mTorr
The structural analysis of the sputtered thin films was performed by Xray diffractometer (XRD, Rigaku XRDTM) at diffraction angles 2θ, ranging from 10° to 80°
Summary
Cuprous oxide (Cu2O) is a well-established p-type material and its conductivity is directly correlated with the oxygen rich or poor layers due to the variation in growth processes [1]. Such growth processes usually result in copper (I) oxide Cu2O and copper (II) oxide CuO (i.e. cupric oxide) [2,3] films mainly due to the oxidization process of copper films. The optical properties vary for both Cu2O and CuO as reported previously [47] mainly due to the growth process resulting in rich or poor oxygen bonding. Copper oxide films show high transparency with light absorbing capability at wavelengths below 600 nm, whereas metal rich oxide films absorbs strongly in the visible spectrum range [2]
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