Electrostatically assembled CsCu₂Br₃/Ag₂Se type-II heterojunction nanocomposite for self-powered broadband...

The synthesis of efficient heterojunction nanocomposite with optimized carrier dynamics remains a key challenge in material design. Herein, we report the electrostatic assembly of a CsCu₂Br₃/Ag₂Se heterojunction nanocomposite, in which oppositely charged nanocrystals spontaneously integrate through electrostatic interactions, forming intimate interfacial contact and thereby enhancing carrier transfer. The resulting type-II band alignment induces carrier redistribution at the interface and generates an internal electric field that enables carrier separation without the need for external bias. Density functional theory calculations and ultraviolet photoelectron spectroscopy results confirm the type-II alignment, providing insights into interfacial carrier dynamics. The device exhibits a broadband photoresponse from 405 to 1550 nm, with high photocurrent, reduced noise, and rapid response times (37.1 and 28.4 μs for rise and decay, respectively). Furthermore, the device exhibits stable performance, high-frequency modulation (∼7 kHz), and spatially resolved photocurrent mapping, indicating its potential for near-infrared imaging. Overall, the results demonstrate that electrostatic assembly is an effective strategy for engineering type-II heterojunction interfaces for self-powered broadband photodetection.