P-Type Ni-Doped α-GaCrO3 (α-GaCrO3:Ni) Thin Films: Investigations of Structural, Optical, and Electronic Properties for Hole Transport Layer and Transparent Photodetector Applications

Abstract

Nickel-doped gallium chromium oxide (α-GaCrO3:Ni) thin films were investigated for their potential application as hole transport layers (HTLs) in perovskite solar cells and as p-type transparent conducting oxide (TCO) in p–n junction-based photodetectors. Epitaxial α-GaCrO3:Ni thin films were deposited on sapphire substrates by RF magnetron sputtering under varying oxygen partial pressures, and their structural quality was determined by X-ray diffraction measurements. The film grown at 20% oxygen partial pressure exhibited lowest ω-scan full width at half maxima (fwhm) values of ∼330 arcsec for the out-of-plane (0006) diffraction peak and ∼1855 arcsec for the in-plane (20–28) diffraction peak. Optical characterization of the film revealed a large optical band gap of 4.1 eV and exhibited an average transparency of more than 70%. Photoelectron spectroscopy measurements confirmed a high ionization energy of 5.7 eV for the thin films, which is well aligned with the perovskite active layer having deep valence band maxima (VBM) like MaPbBr3 and CsPbBr3. Atomic force microscopy and X-ray reflectivity analyses confirmed two-dimensional film growth with smooth surfaces and interfaces. Transmission electron microscopy reveals a sharp and well-defined film–substrate interface. P-type conductivity of the thin film was confirmed by Seebeck measurements, while I–V measurement with platinum (Pt) contacts demonstrated Ohmic behavior at room temperature. These findings suggest that its structural suitability for n-type transparent conducting oxides (TCOs) integration and the alignment of work function with the perovskite having deep VBM makes it a prominent candidate as a HTL in solar cells and p-type TCO for p–n junction photodetectors.