Atomic-layer-deposited Cu_xCr_yO_z thin films: Optoelectronic properties and potential application as hole-selective contacts for c-Si solar cells

In this work, we investigate the properties of Cu_xCr_yO_z thin films deposited by atomic layer deposition (ALD) over a wide compositional range. A significant increase in growth rate is observed for intermediate compositions and shown to arise from an enhancement of the CrO_x deposition rate on the CuO_x surface. In addition to the characteristics of the deposition process, we explore the structural and optoelectronic properties of these films for compositions ranging from copper-free chromium oxide to chromium-free copper oxide, and for various post-deposition annealing temperatures (400–800 °C). The resulting composition, optical constants, band gap, valence band maximum and work function are determined and used to draw full band diagrams of the binary and ternary oxides. We report for the first time the experimental work function of the spinel phase CuCr₂O₄ (5.0 ± 0.2 eV). Finally, the contact resistivity of the films with p-type silicon is examined to assess their potential use as hole-selective contacts for crystalline Si solar cells. The lowest contact resistivity (1.72 Ω cm²) was found for as-deposited Cu_0.05Cr_0.30O_0.65.