Layered Bi₂O₂Se nanosheets, characterized by a low bandgap, high electron mobility, and good air stability, have garnered significant attention for their potential applications in electronics and photonics. However, the relatively low photocurrent generated by single Bi₂O₂Se nanosheet photodetectors results in diminished switching ratios and responsiveness, thereby limiting the overall performance of Bi₂O₂Se-based photodetectors. In this study, we report a dual-band heterostructure photodetector constructed from high-quality Bi₂O₂Se nanosheets and CdS nanobelts. This device demonstrates exceptional photodetection performance in both the visible (450 nm) and near-infrared (1150 nm) regions, featuring a high switching ratio, increased responsivity, elevated specific detectivity, large external quantum efficiency, and rapid response speed. Notably, these key parameters exceed those reported in most Bi₂O₂Se-based photodetectors. Importantly, the Bi₂O₂Se/CdS heterostructure photodetector showcases impressive high-resolution imaging capabilities. These findings highlight the promising potential of this device for applications in image sensing and encrypted optical communication.

Flexible solid-state cooling devices with high efficiency are attracted to ferroelectric polymers with excellent negative electrocaloric (EC) effects. It is challenging to obtain a large negative EC effect in ferroelectric polymers due to the lack of tunable techniques. A giant negative EC response was obtained in the poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE), 70/30, in mole ratio) irradiated with high-energy X-ray. The irradiated P(VDF-TrFE) films showed an adiabatic temperature change of −13.5 K at 40 MV/m under a dose of 5 Mrad (1 Mrad=10⁴ J/kg) obtained by the indirect method. This significant negative EC effect is attributed to the enhancement of crystalline due to the entry of polymer molecules into the amorphous to crystalline structure and the reduction of heat capacity due to the increase of crosslinking. In addition, X-ray irradiation improves the dielectric coefficient from 15 to 22. This research indicates that irradiation can modify the negative EC properties of ferroelectric polymers for solid-state cooling.