The ability of MXenes to efficiently absorb light is greatly enriched by the surface plasmons oscillating at their two-dimensional (2D) surfaces. Thus far, MXenes have shown impressive plasmonic absorptions spanning the visible and infrared (IR) regimes. However, their potential use in IR optoelectronic applications, including photodiodes, has been marginally investigated. Besides, their relatively low resistivity has limited their use as photosensing materials due to their intrinsic high dark current. Herein, heterostructures made of methylammonium lead triiodide (MAPbI3) perovskite and niobium carbide (Nb2CTx) MXene are prepared with a matching band structure and exploited for self-powered visible-near IR (NIR) photodiodes. Using MAPbI3 has expanded the operation range of the MAPbI3/Nb2CTx photodiode to the visible regime while suppressing the relatively large dark current of the NIR-absorbing Nb2CTx. In consequence, the fabricated MAPbI3/Nb2CTx photodiode has responded linearly to white light illumination with a responsivity of 0.25 A/W and a temporal photoresponse of <4.5 μs. Furthermore, when illuminated by NIR laser (1064 nm), our photodiode demonstrates a higher on/off ratio (∼103) and faster response times (<30 ms) compared to that of planar Nb2CTx-only detectors (<2 and 20 s, respectively). The performed space-charge-limited current (SCLC) and capacitance measurements reveal that such an efficient and enhanced charge transfer depends on the coordinate bonding between the surface groups of the MXene and the undercoordinated Pb2+ ions of the MAPbI3 at the passivated MAPbI3/Nb2CTx interface.
Keywords: absorption; capacitance; photoresponse; surface passivation; surface plasmons.