Near infrared light-sensing semi-transparent organic phototransistors with soluble benzothiadiazole-based conjugated polymer films

Here we report semi-transparent organic phototransistors (OPTRs), which consist of poly[{3-(5-(7-methyl-5,6-bis(octyloxy)benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)-6-(5-methylthiophen-2-yl)}-co-{2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione}] (PDPP-8OBT) as a sensing channel layer, for the detection of particular near infrared (NIR) light (905 nm) that is used in the light and distance ranging (LiDAR) systems. Two different thicknesses (45 and 75 nm) were chosen for the examination of NIR light-sensing performances, while both ca. 20 nm-thick silver source/drain electrodes and transparent indium-tin oxide (ITO) gate electrodes were applied to achieve the semi-transparency of devices. Results showed that the present devices could be operated in a mode of typical p-channel transistor and were sensitive to the NIR light. The semi-transparent OPTRs with the 75 nm-thick PDPP-8OBT layers showed better NIR light-sensing performances with the high photosensitivity of ca. 200 %. The performance of devices was slightly varied by running about 50 cycles of transfer curves between forward and backward sweeps, whereas the NIR light-sensing characteristics were well kept during the cycle tests. It is expected that the present NIR-OPTRs with the PDPP-8OBT sensing channel layers can be applied as a practical detector for LiDAR systems through further optimization of device stability. Semi-transparent organic phototransistors with the PDPP-8OBT sensing channel layers can detect near infrared (NIR) light with a high photosensitivity of ca. 200%. [Display omitted] •Synthesis of NIR light-absorbing conjugated polymer (PDPP-8OBT).•Semi-transparent organic phototransistors with the PDPP-8OBT sensing channel layers.•High photosensitivity (