Large-scale preparation of ultra-long ZnSe–PbSe heterojunction nanowires for flexible broadband photodetectors

Flexible photodetectors show great applications in wearable electronics such as health monitoring and the Internet of Things. In this study, we have prepared ultralong ZnSe–PbSe heterojunction nanowires with a length of 20 μm in gram-scale by an in-situ cation exchange reaction. The produced PbSe nanoparticles on the ZnSe nanowire configuration are close to an ideal heterojunction system due to the small lattice mismatch of 7.4% in the (111) direction. The Ohmic contact is formed for nanowire photodetectors. The ZnSe–PbSe heterojunction nanowire photodetector exhibits a broadband photoresponse with the peak responsivity of 40 A W−1 while the ZnSe nanowire photodetector shows a narrowband photoresponse of 5 A W−1, as a result of its extended absorption across the entire UV-visible-NIR. Electrons are transported from PbSe to ZnSe while holes are trapped at PbSe, and electrons are extracted to an external circuit by an Al electrode, resulting in a high gain of the photoconductor. The broadband photoresponse, the large linear dynamic range of 66 dB, the fast response speed of 0.02 s and the protracted cycle of 5000 show the feasibility of the flexible heterojunction photodetector.