In this Letter, we report a high-performance NiO/β-Ga2O3 pn heterojunction diode with an optimized interface by annealing. The electrical characteristics of the pn diode without annealing (PND) and with annealing (APND) are studied systematically. The APND device has a lower specific on-resistance of 4.1 mΩ cm2, compared to that of the PND, 5.4 mΩ cm2. Moreover, for the APND, a high breakdown voltage of 1630 V with lower leakage current is achieved, which is 730 V higher than that of the PND. The enhanced electrical performance of the APND leads to a record high power figure of merit of 0.65 GW/cm2 in Ga2O3-based pn diodes, which is among the best reported results in Ga2O3 power devices. In addition, the interface trap density of the diode decreases from 1.04 × 1012 to 1.33 × 1011 eV−1 cm−2 after annealing, contributing to much lower hysteresis. Simultaneously, the ideality factor n for the APND is steady at elevated temperatures due to the stable interface. The results of C−V characteristics reveal the bulk defects inside the nickel oxide film grown by sputtering, which are calculated by high- and low-frequency capacitance methods. X-ray photoelectron spectroscopy of NiO illustrates the reasons for the changes in the concentration of holes and defects in the film before and after annealing. This work paves the way for further improving the performance of Ga2O3 diode via interface engineering.

Combing PV with Thermoelectric (TE) would be dominant because it can employ the solar fully spectrum to produce electricity. But the TE efficiency is significantly lower than PV efficiency and the coupling effect between them will limit the performance of PV and TE. The analyze and comparison on the different characteristics among the hybrid module, the PV alone and TE alone is significant to obtain the highest the electrical efficiency. In this paper, the attention was paid to the inconsistent phenomenon of thermoelectric load resistance for photovoltaic-thermoelectric modules. The model of PV-TE was built and verified based on two types of PV cells. The load resistance of TE for the maximum power output was also analyzed under different working conditions for the TE alone, TE in the PV-TE and PV-TE. The results showed that the load resistance of TE for the maximum power output of the TE alone, TE in the PV-TE and PV-TE are all different. For example, the PV-TE module based on the c-Si cell attains its peak value at the load electrical resistance of TE of 0.75 Ω, while the internal electrical resistance of the TE is 0.47 Ω. The PV-TE module based on the GaAs cell shows a maximum efficiency of PV-TE with a load resistance of approximately 1.6 Ω, while the internal electrical resistance of the TE is 2.0 Ω. Referring to the load resistance of TE alone is not suitable for PV-TE maximum power output. In addition, the TE maximum power output does not correspond to the PV-TE maximum power output since the TE load resistances in these two conditions are also different. The study will provide the reference for attaining the correct load resistance for the actual maximum power output of PV-TE module.

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Rapid economic and industrial development within the past decades has led to an increased consumption of non-renewable and polluting fossil fuels. Therefore, it is of utmost importance to explore renewable energy sources to meet the increased demand for energy [1,2]. In addition, issues such as: scarcity of conventional energy sources, hike in fuel prices and environmental pollution has made the generation of power from conventional energy sources to be unsustainable and unviable [3]. The sun is one of the most potent energy sources as its contribution to the world's energy demand is substantial and its availability greatly exceeds any conceivable future energy demands [4]. Solar energy is therefore one of the most widely abundant and used renewable energy source. The most common method to utilize solar energy is to convert it into two easily harnessed forms which are; electrical and thermal energy [5].Solar photovoltaic (PV) systems can be used to convert solar radiations directly into electricity via the Photovoltaic effect. It is considered as one of the most viable solution to meet the electrical energy demand and demand for clean energy as it can achieve noiseless operation, needs low maintenance and has zero pollution [6]. However, the major issues hindering the widespread application of the PV are: limited conversion efficiency, elevated temperature and dust accumulation [7].A thermoelectric generator (TEG) is a device which can convert waste heat directly into electrical energy via the Seebeck effect and it has attracted substantial interest recently because of its advantages such as: silent operation and compactness [8]. A hybrid device can be obtained by integrating a thermoelectric generator into a photovoltaic module to compensate for the disadvantages of the photovoltaic (elevated temperature) by using the

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