Ultrathin CuBi2O4 on a bipolar Bi2O3 nano-scaffold: a self-powered broadband photoelectrochemical photodetector with improved responsivity and response speed

CuBi2O4 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 Bi2O3 host scaffold was coupled with an ultrathin CuBi2O4 light absorbing layer to construct a host-guest Bi2O3/CuBi2O4 photocathode. The work function of the bipolar Bi2O3 scaffold lies in between FTO and CuBi2O4, making Bi2O3 a suitable back contact layer for hole transport. Compared with the flat CuBi2O4 and Bi2O3 scaffold counterpart, the nanostructured Bi2O3/CuBi2O4 exhibits significantly improved light absorption and enhanced charge separation efficiency. The Bi2O3/CuBi2O4 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-1 and a remarkable short response time of 0.18 ms/0.19 ms. Bi2O3/CuBi2O4 prepared by magnetron sputtering demonstrates great potential for rapid PEC photodetection in a wide optical domain.