Binary copper oxide semiconductors: From materials towards devices

TLDR

Copper‑oxide semiconductors can be tuned from insulating to metallic conduction, with bandgaps ranging from 2.1 eV to 1.40 eV, placing them near the optimal efficiency window for solar‑cell applications. The paper reviews the experimentally observed and theoretically predicted material properties of the three binary phases Cu₂O, Cu₄O₃, and CuO, and presents new experimental data. Thin‑film deposition techniques are used to grow these phases, and the resulting films are characterized by spectroscopic and structural methods to assess their electronic and optical behavior. Device‑level results show that a p‑Cu₂O/n‑AlGaN heterojunction yields superior solar‑cell performance compared to the previously favored p‑Cu₂O/n‑ZnO configuration, as confirmed by XPS analysis.

Abstract

Abstract Copper‐oxide compound semiconductors provide a unique possibility to tune the optical and electronic properties from insulating to metallic conduction, from bandgap energies of 2.1 eV to the infrared at 1.40 eV, i.e., right into the middle of the efficiency maximum for solar‐cell applications. Three distinctly different phases, Cu 2 O, Cu 4 O 3 , and CuO, of this binary semiconductor can be prepared by thin‐film deposition techniques, which differ in the oxidation state of copper. Their material properties as far as they are known by experiment or predicted by theory are reviewed. They are supplemented by new experimental results from thin‐film growth and characterization, both will be critically discussed and summarized. With respect to devices the focus is on solar‐cell performances based on Cu 2 O. It is demonstrated by photoelectron spectroscopy (XPS) that the heterojunction system p‐Cu 2 O/n‐AlGaN is much more promising for the application as efficient solar cells than that of p‐Cu 2 O/n‐ZnO heterojunction devices that have been favored up to now.