Water‐Resistant Polymer Films of Cyan‐Emitting CsPbBr 2.1 Cl 0.9 Perovskite Nanocrystals for Underwater Wireless Optical Communication

Underwater wireless optical communication (UWOC) holds great promise for applications in deep‐sea exploration, marine environmental monitoring, and underwater sensing, owing to its high bandwidth, low latency, and strong anti‐interference capability. Perovskite nanocrystals are considered ideal light‐source candidates for UWOC due to their emission tunability matching seawater's low‐loss window, high photoluminescence efficiency, ultrafast radiative recombination, and solution processability. However, poor water stability of perovskite nanocrystals originating from their intrinsic ionic lattice severely restricts their practical deployment in underwater environments. Herein, we report a synergistic strategy combining 2‐thiophenesulfonamide coordination passivation and isobornyl acrylate ultraviolet‐induced polymerization to prepare solution‐processable and water‐resistant polymer CsPbBr 2.1 Cl 0.9 perovskite nanocrystal films. 2‐thiophenesulfonamide passivates undercoordinated surface defects and enables stable perovskite nanocrystal dispersion in isobornyl acrylate monomer, while in situ ultraviolet‐polymerized isobornyl acrylate produces a dense protective polymer network to shield perovskite nanocrystals from water erosion. These composite films show outstanding water stability with a negligible emission intensity loss after 8 h of immersion in water. Integrated as a color‐conversion layer in a UWOC system, the perovskite nanocrystal‐based light‐emitting diode delivers a stable −3 dB bandwidth of 2.9 MHz. Using non‐return‐to‐zero amplitude shift keying modulation, the system achieves a data transmission rate of 3.48 Mbps.