Enhanced Bandwidth of Blue‐Green‐Light CsPbBr₃ Perovskite Photodetectors toward Underwater Wireless Optical Communication

All inorganic CsPbBr 3 perovskite offers excellent thermal stability and a naturally narrow blue‐green spectral response, making it well‐suited for underwater wireless optical communication (UWOC). However, its practical application is hindered by the slow response speed and limited bandwidth of existing CsPbBr 3 ‐based photodetectors. In this work, a carbon‐copper (C‐Cu) composite electrode to achieve rapid response and high bandwidth in CsPbBr 3 photodetectors is introduced. The composite electrode enhances carrier extraction by improving the conductivity of the carbon layer. More importantly, small amounts of copper from the C‐Cu electrode can reach the CsPbBr 3 layer to act as an effective dopant to passivate shallow defects in perovskite, which results in significantly increased carrier mobility and reduced trap density. As a result, the C‐Cu‐based photodetectors exhibit a shortened fall time of 406 ns and a −3 dB bandwidth of up to 3 MHz, which is the highest value among reported CsPbBr 3 ‐based photodetectors. Additionally, when deployed as a receiver in a prototype UWOC system, the photodetectors achieve a high data rate of 20 Mbps. Overall, this work presents a promising strategy to enhance the bandwidth of CsPbBr 3 ‐based photodetectors, advancing their potential for high‐speed underwater wireless optical communication.