Ultraviolet–Visible photo-response of p-Cu2O/n-ZnO heterojunction prepared on flexible (PET) substrate

• Fabrication of p-Cu2O/n-ZnO heterojunction on flexible PET substrate.
• Synthesis of different ZnO nanostructures i.e. nanoneedles, nanotubes and nanorods.
• The UV-VIS photo-detection properties of p-Cu2O/n-ZnO heterojunctions.

The deposition of monocrystalline ZnO nanostructures (using different concentration of reaction solution) on Cu2O thin film by hydrothermal method is reported. The mechanism of growing different ZnO nanostructures i.e. nanoneedles, nanotubes and nanorods are explained based on the gradient of Zn+ species (resulting from precipitation) in reaction solution. The UV-VIS photo-detection properties of the three selected p-Cu2O/n-ZnO heterojunctions are studied by illuminated I–V characteristic and the wavelength dependent photo-responsivity properties. The spectral responsivity curves can be divided into three regions (1.9–2.17 eV), (2.2–2.9 eV) and (>3.2 eV) denoted as A, B and C. The regions A and C are assigned for band to band level absorption in Cu2O and ZnO respectively, while region C is associated with a combination of two absorption process: part of photons were absorbed by the band to deep level absorption in ZnO and the transmitted photons were absorbed in Cu2O. It is found that the heterojunctions with nanotubes exhibit higher responsivity than other nanostructures, which is mainly due to the large surface-to-volume ratio.