Pronounced Light Insensitivity in Low-Voltage n-Channel Organic Field-Effect Transistors with Channel Layers of Dinitrobenzothiadiazole-Containing Conjugated Polymer

A light insensitivity in organic field-effect transistors (OFETs) is crucial for use under ambient light conditions that can cause additional current flow in devices leading to unexpected noises. Here, we report low-voltage driving n-channel OFETs, featuring very low light sensitivity, with a channel layer consisting of dinitrobenzothiadiazole-containing conjugated polymer, poly[{2,5-bis(2-octyldodecyl)-3,6-bis(thien-2-yl)-pyrrolo[3,4-c]pyrrole-1,4-diyl}-co-{2,2′-(5,6-dinitro-2,1,3-benzothiadiazole)-5,5′-diyl}] (PODTPPD-DNBT). The PODTPPD-DNBT polymer, synthesized via the Stille reaction of two comonomers, showed an optical absorption up to 1100 nm and a lowest unoccupied molecular orbital (LUMO) energy of 4.41 eV. The OFET devices with the PODTPPD-DNBT channels exhibited n-channel-mode transistor behaviors at a low voltage (≤5 V) and very slightly increased drain current under illumination with strong near-infrared (NIR, wavelength = 905 nm, intensity = 5.96 mW/cm2) and simulated solar light (intensity = 100 mW/cm2). The PODTPPD-DNBT channel layers delivered very low photoresponsivity of 6.95 mA/W under the NIR light, which is less than 1% compared to the theoretical maximum value of 730 mA/W, and 2800% lower photoresponsivity (0.3 mA/W) compared to the same backbone polymer (PODTPPD-BT) without dinitro groups under the simulated solar light.