Flexible Photothermoelectric Photodetector Based on Plasmonic Cu ₉ S ₈ Recycled from Waste Copper Etching Solution

Abstract The self‐powered photothermoelectric photodetector is promising for diverse military and civilian applications. However, the substandard mechanical flexibility and high manufacturing costs limit its promotion in wearable electronics. Herein, a cost‐effective route is demonstrated for manufacturing a flexible photothermoelectric photodetector using industrial waste. By the precipitation reaction under the coupling of ultrasonic waves and shear force, waste copper etching solution is successfully recycled into copper sulfide nanoparticles. The resulting plasmonic Cu 9 S 8 nanoparticles, with an average size of ≈10 nm, exhibit strong near‐infrared light absorption as well as the high photothermal conversion efficiency of 48% due to the plasmonic enhancement effects. Then, the flexible photothermoelectric device is fabricated by depositing the Cu 9 S 8 thin film on Nylon filter membranes. The simplified device demonstrates a responsivity of 0.3 mA W −1 and a rapid response time of 4.1 s (rise) and 3.0 s (fall) to 808 nm infrared light. Furthermore, microcrack engineering within the Cu 9 S 8 thin film enhances the device's mechanical durability. The flexible photodetector shows almost no degradation in photoresponse even after 1000 bending‐releasing cycles. This work not only provides a way to turn waste etching solution into treasure, but also opens up a new path for low‐cost preparation of flexible photodetectors.