Near-Infrared Organic Phototransistors with p-Channel Photosensitive Layers of Conjugated Polymer Composed of bis-Octyldodecyl-Diketopyrrolopyrrole and Benzothiadiazole Units

초록

A near-infrared (NIR)-absorbing 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 '-(2,1,3-benzothiadiazole)-5,5 '-diyl}] (PODTPPD-BT), which is synthesized via a Stille coupling reaction, can play a dual role (charge transport and sensing) in NIR-sensing organic phototransistors (OPTRs). The PODTPPD-BT films, which feature two strong optical absorption peaks at wavelengths (lambda) of 830 and 935 nm, possess a highly ordered crystalline state as evidenced by the synchrotron radiation grazing incidence X-ray diffraction (GIXD) method. The OPTRs with the PODTPPD-BT layers show typical p-channel transistor behaviors in the dark, while their best dark performance is measured at a PODTPPD-BT thickness (t) of 85 nm. The highest overall photocurrent is measured at t = 85 nm under illumination with three monochromatic NIR lights, while the highest photoresponsivity (R-C) is obtained for the thickest PODTPPD-BT layers (t = 145 nm). The flexible OPTRs with the PODTPPD-BT layers demonstrate stable sensing characteristics upon optical on/off modulations using a high-power NIR laser diode (lambda = 905 nm) used for actual light detection and ranging (LiDAR) systems.

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