See-through metal oxide frameworks for transparent photovoltaics and broadband photodetectors

In this work, we report metal-oxide based fast and stable transparent self-powered broadband (UV to NIR) photovoltaic devices. Using sputtering technique, we prepared the large-scale and transparent metal-oxide heterojunction device by formation of p-Cu-Cu2O/n-ZnO films on a FTO glass substrate. The heterojunction of Cu-Cu2O/ZnO is invisible to human eyes due to its high energy bandgap to render high transparency ( > 80%) for long wavelength light within the range 600-1100 nm. Meanwhile, it strongly absorbs short wavelength of UV light (below 400 nm), which may cause hurts to human eyes or skin cancers. The transparent Cu-Cu2O/ZnO device is the invisible electric power generator due to photovoltaic behaviour with the open-circuit-voltage of 0.36 V and high short-circuit-current value (1.83 mA), resulting in the maximum conversion efficiency of 0.405%. In addition, the transparent Cu-Cu2O/ZnO photovoltaic device also works as the self-operating photodetector. In the photovoltaic mode, Cu-Cu2O/ZnO heterojunction provided the fast and stable photoresponse (rise time similar to 3.89 ms and decay time similar to 4.12 ms) towards white light which is considered to be the fastest performance of Cu2O/ZnO based thin film photodetectors. These results represent a significant advancement in the see-through photovoltaic device with low-cost and evidently high efficiency. We may consider the transparent window as a power generator to provide electric energy on-demand sites, such as buildings, houses, or vehicles, while protected from the harmful UV radiation due to the smart functioning window.