Self-powered hematite photoelectrochemical photodetectors for blue-green light encrypted underwater optical...

Photoelectrochemical photodetectors (PEC PDs) are attractive for underwater optical communication (UOC) because they are low-cost, highly sensitive, and can operate in an aqueous environment without an external power supply. However, UOC systems that combine high sensitivity with encryption capability remain difficult to realize. Herein, we report a self-powered α-Fe₂O₃ nanosheet-array PEC PD and demonstrate a transient-polarity-based encoding strategy for encrypted UOC. The device exhibits broadband photoresponse from 365 to 523 nm, a responsivity of 10.34 mA W^-1, and rapid rise/decay times of 3/2 ms at zero bias. More importantly, reproducible positive and negative transient photocurrent pulses are generated during light switching because of carrier trapping and detrapping at the α-Fe₂O₃/electrolyte interface. These opposite pulse polarities are directly assigned as binary states, enabling forward and reverse decoding of the same optical signal and encrypted character transmission. This work transforms an intrinsic interfacial carrier-dynamic feature into a functional information-encoding dimension, providing a new design principle for compact and secure PEC-based UOC.