pH-dependent deposition of Cu₂O thin films: tuning defect states and electronic properties for improved energy conversion applications

Abstract

This research investigates the electronic and optical properties of Cu₂O nanostructures deposited under different pH conditions and their implications for semiconductor applications. We performed a comprehensive electrochemical characterization using Mott-Schottky (M-S) analysis to determine the type of conductivity, charge carrier density, and flat-band potential of Cu₂O thin films. The results indicated that Cu₂O deposited at pH 5.4 exhibited n-type conductivity with a peak charge carrier density of 1.01 × 10¹⁵ cm^− 3, while Cu₂O deposited at pH 10 showed p-type conductivity with a carrier density of 2.07 × 10¹⁷ cm^− 3. Results showed that the prepared Cu₂O thin films were influenced by the pH and displayed different semiconductor, crystal, and morphological properties. The optical absorption edge appeared around 459 nm which indicates the formation of Cu₂O and the band gap energy was estimated using Tauc plot. Photoluminescence (PL) spectroscopy was utilized to identify and characterize defect states within the band gap, revealing significant peaks related to copper and oxygen vacancies, as well as metastable defects. The energy band diagrams and Schottky barrier potential calculations provided insights into the charge transfer mechanisms at the semiconductor-electrolyte interface. Finally, the performance of p-Cu₂O/n-Cu₂O homojunctions was evaluated through I-V characterization, demonstrating typical p-n junction behavior and a conversion efficiency of 0.374%. This study highlights the influence of deposition conditions on the electronic properties of Cu₂O and underscores the importance of optimizing these parameters for enhanced performance in photoelectrochemical devices.