Ultrahigh and Tunable Negative Photoresponse in Organic-Gated Carbon Nanotube Film Field-Effect Transistors

Negative photoconductance (NPC) detectors have attracted continuous attention for constructing advanced and novel optoelectronic devices, including reconfigurable image sensors and optosynaptic systems, especially by combining NPC with positive photoconductance (PPC). However, NPC devices suffer from much lower photosensitivity, slower response speed, and poor stability, especially in the infrared range. In this work, controllable NPC detectors based on organic-gated carbon nanotube field-effect transistors (OG-CNT FETs) are reported and the strong influence of light-induced electrostatic doping on the nonconventional photoresponse is demonstrated. The PM6/Y6-based heterojunction allows efficient near-infrared light absorption and facilitates exciton diffusion. By introducing a floating gate structure with an ultrathin dielectric layer, the OG-CNT FET shows an enhanced NPC effect owing to in situ signal amplification. Compared to other device configurations, the optimal OG-CNT FETs exhibit high responsivity of 72.6 A W-1 at 880 nm, along with improved response/recovery times of 7 and 5 ms. Impressively, gate-tunable switching between NPC and PPC is observed under the same light illumination. The reversible switching can be attributed to the competition between the light-controlled electrostatic coupling and the PM6/Y6 photovoltaic effect, which offers a new approach to achieve bidirectional photoresponses and paves the way for the development of future multifunctional optoelectronic systems.