Ti₄N₃ MXene based flexible near-infrared photodetector

Progress in understanding optoelectronic properties of the two-dimensional (2D) transition metal carbides and nitrides (MXenes) is hindered by a dearth of exploring novel intrinsic semiconductor materials from MXene families. Here, we prepared 2D Ti₄N₃ MXene nanoflakes via the molten salt etching method, which was then employed to fabricate a flexible broadband near-infrared (NIR) photodetector. The assembled Ti₄N₃ MXene based photodetector exhibits a stable response to the lasers of 808, 852, 915, 980, and 1060 nm. Under high-power IR illumination, the device deviates entirely from conventional positive photoconductivity, displaying an anomalous superlinear negative photoresponse with a power-law exponent of α = 1.54 and a response time of ~0.7 s. The negative photoconductivity behavior of the Ti₄N₃ MXene based devices is driven by a robust photothermal-ionotronic coupling mechanism: the intense IR-induced local heating heavily disrupts the interfacial hydrogen-bonding networks, triggering an Arrhenius-type non-linear desorption of confined water and protons that effectively disconnects the ionic conduction pathways. This work provides fundamental insights into the photothermal-dominated carrier and ion dynamics in 2D materials, paving the way for next-generation optoelectrical devices and neuromorphic sensory systems.