Demonstration of Low-Resistive P-Type Cu4O3 Thin Films by Radio Frequency Sputtering for Low-Cost Thin Film Solar Cells

Abstract

A systematic investigation on the influence of oxygen flow rates and substrate positions on the structural, optical and electrical properties of copper oxide (Cu x O) thin films deposited by reactive radio frequency sputtering to establish the deposition condition for Cu 4 O 3 . Detailed analyses on x-ray diffraction (XRD) and Raman spectroscopy were performed, revealing that different single or bi-phase of Cu 2 O, Cu 4 O 3 and CuO were grown at the different O 2 flow rate and substrate position. From the optical absorption analyses, Cu 2 O films showed a direct forbidden transition at $\mathrm{E}_{\mathrm{g}}=2.28\sim 2.37 \text{eV}$ in addition to a direct allowed transition at $\mathrm{E}_{\mathrm{g}}=2.50\sim 2.53 \text{eV}$ . In Cu 4 O 3 and CuO films, a direct forbidden transition at $\mathrm{E}_{\mathrm{g}}=1.58 \text{eV}$ and 1.51 ∼ 1.54 eV was observed respectively with a high absorption coefficient, demonstrating the possibility to use these compounds as an absorber for single junction solar cells. Moreover, single phase Cu 4 O 3 showed the resistivity from 38 to 460 ohm cm with p-type conductivity, which was the lowest resistivity for the single phase of Cu 4 O 3 films reported so far.