Ultrathin CuBiO on a bipolar BiO nano-scaffold: a self-powered broadband photoelectrochemical photodetector with improved responsivity and response speed.

CuBiO is a promising photoactive material for photoelectrochemical (PEC) broadband photodetectors due to its suitable band structure, but its photo-responsivity is severely limited by the short carrier diffusion length and long light penetration depth. To address the trade-off between light absorption and charge separation, a nano-structured bipolar BiO host scaffold was coupled with an ultrathin CuBiO light absorbing layer to construct a host-guest BiO/CuBiO photocathode. The work function of the bipolar BiO scaffold lies in between FTO and CuBiO, making BiO a suitable back contact layer for hole transport. Compared with the flat CuBiO and BiO scaffold counterpart, the nanostructured BiO/CuBiO exhibits significantly improved light absorption and enhanced charge separation efficiency. The BiO/CuBiO PEC photodetector can be self-powered and demonstrates a broad photo-response ranging from ultraviolet (UV) to near infrared (NIR). It shows a high responsivity of 75 mA W and a remarkable short response time of 0.18 ms/0.19 ms. BiO/CuBiO prepared by magnetron sputtering demonstrates great potential for rapid PEC photodetection in a wide optical domain.