Wide-Band-Gap p-Type GaCrO3:Ni Semiconductor: A Hole Transport Material

The hole transport layer (HTL) is a crucial part of perovskite and organic semiconductor-based photovoltaic devices in order to improve its efficiency by suppressing the excess charge carrier recombination and providing a better contact for charge transport. In this work, Ni-doped alpha-GaCrO3 is studied to investigate its suitability as a HTL material. Single-phase polycrystalline alpha(NixGa0.9-x)Cr1.1O3 (0 < x < 0.02) materials are synthesized using the solid-state reaction method. The solubility of Ni in alpha-GaCrO3 is investigated using synchrotron X-ray diffraction measurements, which is found to be up to x = 0.01. Ni doping improves the delocalization of the charge carriers, which results in the reduction of the resistance by around 104 times as compared to the undoped material. The electrical properties of Ni-doped alpha-Ga0.9Cr1.1O3 are also compared with those of the Ni-doped alpha-Cr2O3. Ni-doped alpha-Ga0.9Cr1.1O3 shows better electrical properties due to modification in the valance band of alpha-Ga0.9Cr1.1O3 which further enhances the delocalization of charge carriers. Nature of charge carrier is confirmed to be p-type (positive) using Seebeck measurements. Ionization energy of Ni-doped alpha-Ga0.9Cr1.1O3 is determined using Ultraviolet Photoelectron Spectroscopy measurements and found to be about 5.2 +/- 0.2 eV. The ionization energy is comparable to the most of state-of-the-art active layers used in perovskite and organic semiconductor-based photovoltaic devices. Thus, Ni-doped p-type alpha-Ga0.9Cr1.1O3 with band gap of around 3.95 eV and ionization energy of about 5.2 +/- 0.2 eV is proposed to be as a promising candidate for the HTL.