Polypyrrole-Engineered ZnO/BiOBr Nanostructured Heterojunction with Broadband UV-Visible Optical Sensing Properties

Abstract Extending the spectral response of wide-bandgap semiconductors into the visible region remains a significant challenge for broadband UV-visible optical sensing. Herein, a polypyrrole (PPy)-engineered ZnO/BiOBr nanostructured heterojunction was developed to enhance visible-light harvesting and improve broadband optical sensing properties. The hybrid heterojunction combines the ultraviolet response of ZnO, the near-visible UV photoactivity of BiOBr, and the high electrical conductivity of the π-conjugated PPy network, resulting in enhanced light absorption, efficient charge separation, and improved charge transport. The ZnO/BiOBr-PPy heterojunction exhibits a responsivity of 0.104 AW−1, corresponding to an approximately 5.7-fold enhancement compared with ZnO/BiOBr, together with more than an order-of-magnitude enhancement in visible-light photocurrent. Furthermore, its stable switching behavior with rapid response and recovery characteristics demonstrates excellent broadband optical sensing performance. Ultraviolet photoelectron spectroscopy (UPS), electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) analyses support the role of PPy in promoting favorable energy-band alignment, facilitating interfacial charge separation, and reducing carrier recombination, thereby contributing to the enhanced photocurrent across the UV-visible spectral region. These findings provide an effective strategy for engineering organic−inorganic nanostructured heterojunctions with enhanced broadband UV-visible optical sensing properties for next-generation optoelectronic sensing applications.