Mosaic Se/InSe Heterojunction for Self‐Powered Bipolar Photodetection

Abstract Broadband, sensitive, and spectrally distinctive photodetectors show great applications in multifunction optoelectronic devices, which usually integrate multiple photodetectors for distinguishing different spectra. Recently, UV‐induced photocurrent polarity‐switching in individual photoelectrochemical photodetectors (PEC PDs) has been demonstrated by tuning the interfacial physical/chemical processes. However, broadband and spectrally distinctive PEC PDs are still scarce. Here, mosaic t‐Se/InSe heterojunctions are used for designing broadband and spectrally distinctive PEC PDs. Mosaic t‐Se/InSe photoelectrodes are fabricated by one‐step electrochemical deposition with annealing treatment. t‐Se/InSe self‐powered PEC PDs show a broadband photoresponse from UV to near‐infrared (NIR). The photocurrent is negative for UV‐visible spectra and turns positive under NIR irradiation. The light‐induced photocurrent polarity‐switching originates from the competition of different redox reactions at the t‐Se/InSe photoelectrode/electrolyte interface. The responsivity is −22.5, −10.93, −4.18, and 2.48 mA W −1 for 365, 525, 630, and 850 nm light, respectively, exceeding most spectrally distinctive solid‐state PDs. The boosted photoresponse of t‐Se/InSe is attributed to the synergistic effect of stronger light absorption, faster carrier transport, and accelerated interfacial charge transfer. Moreover, the devices show great potential for applications in encrypted optical communications. This work provides a way for designing broadband and spectrally distinctive PEC PDs and demonstrates their potential applications.