In-situ SEM evaluation of single-nanowire response in CuO–Cu₂O–ZnO nanowire arrays for infrared energy harvesting

Copper and zinc oxides (CuO, Cu 2 O, ZnO) are semiconductors with p-type and n-type conductivity, respectively, which have attracted attention as perspective materials for the research and development of p-n junction-based devices. Their low cost and abundance are ideal for applications in electronics and solar radiation sensing and harvesting. Most research involving these materials has been focused on UV-VIS photodetectors and solar cells, as well as p-n junction-based diodes. However, less attention has been paid to thermoelectric applications or the detection/energy harvesting of infrared radiation, which constitutes a significant part of the solar spectrum. In this work, electrical properties and the unbiased response to infrared radiation of CuO-Cu 2 O-ZnO heterojunction nanowires are studied. The vertically arranged CuO-Cu 2 O-ZnO nanowire arrays were synthesized directly on copper substrates using a combined thermal oxidation/thermal evaporation method and studied in-situ inside a scanning electron microscope using nanomanipulation techniques. The nanowires were found to exhibit diode-like behavior, indicating the presence of a p-n junction. Furthermore, a pronounced unbiased response to infrared radiation was observed and attributed to the photo-thermoelectrical effect. The estimated Seebeck coefficient, power factor, and responsivity of the CuO-Cu 2 O-ZnO heterojunction nanowires were 120 µV/K, 18 nW/mK 2 , and 150 mA/W respectively. The absorbance capabilities of the material widen the potential for applications in effective harvesting of the full spectrum of solar energy. Additionally, the material furthers the development of nano-power generators operating at low-temperature differences of a few degrees Celsius, which may be favorable for a wide range of applications, like wearable electronics, Internet-of-Things, environmental and health sensors.