NiO–NiTiO₃ Heterojunction for Enhanced Solar Cell Efficiency and Hydrogen Evolution: A Stable All-Oxide Approach

Green energy production has become necessary in order to achieve sustainable development goals and transition toward a green economy where solar energy and hydrogen fuel serve as the forthcoming energy sources. In this aspect, perovskite materials find potential applications in the generation of green hydrogen as well as solar energy. While various halide and lead-based perovskites have shown promising results in photovoltaic technology, their stability and toxicity issues hinder the commercialization of the technology. NiTiO₃ is a stable n-type perovskite oxide with a broad absorption range from ultraviolet to visible near-infrared range. However, the application of oxide perovskite materials has not been explored extensively. The creation of p–n heterojunction in NiO–NiTiO₃ enhances photogenerated charge carrier separation. The interface offers a stronger interaction facilitated through Ti.O bond formation and a characteristic bandgap of 1.27 eV, lower than the individual layers, facilitating charge transfer. This accompanied with the higher density of states in the heterojunction improved the efficiency of NiTiO₃ based solar cell to 4.25% as compared to the previously reported 1.66%. Additionally, the all-oxide device provides 87% efficiency retention after 6 months. Exploring the versatility of this heterojunction, its application in green hydrogen generation has been studied, where the NiO–NiTiO₃ thin-film catalyst yielded an overall hydrogen production of 5.04 mmol g⁻¹/1.68 mmol g⁻¹ h⁻¹ of the catalyst. Therefore, all oxide perovskite heterojunction serves as a prospective candidate for the advancement of renewable energy generation techniques.