Nanoscale Bulk-Heterojunction Channel-Enabled Self-Powered Broadband Lateral Photodetectors for Efficient Weak Light Detection

This work demonstrates a novel technique of fabricating lateral self-powered broadband photodetectors, spanning from visible to near-infrared regions, using a mixed nanoscale ensemble of lead sulfide (PbS) colloidal quantum dots (CQDs) and cesium lead bromide (CsPbBr₃) nanocrystals (NCs). CsPbBr₃ NCs are used to obtain two front benefits. First, they are efficient surface passivators due to their excellent lattice matching with the desired PbS CQDs surface lattice facets. Second, they form an ideal heterojunction with PbS CQDs to generate a built-in potential in the ensemble through the difference between electron and hole quasi-Fermi levels. These effects combined to result in efficient self-powered lateral photodetectors. The synergistic optimization of the ligand exchange process and interface engineering leads to a nearly five-fold increment in charge carrier mobility and a four-fold decrement in trap density. Overall, nano bulk heterojunction devices exhibit a one-order improvement in responsivity and detectivity over the pristine PbS devices. The nano bulk heterojunction-based lateral photodetectors also demonstrate efficient low-intensity photodetection in prototype medical sensing applications.