Near Infrared Organic Phototransistors With Blend Gate Sensing Layers Consisting of Conjugated and Insulating Polymers

Near infrared (NIR) light-detecting organic phototransistors were fabricated with a polymer blend gate sensing layer (GSL). The polymer blend GSLs were prepared by employing a 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)] and an electrically-insulating polymer [poly(methyl methacrylate) (PMMA)] at various PODTPPD-BT contents between 0 and 100 wt%. All the devices with the blend GSLs showed a noticeable drain current increase and threshold voltage shift upon illumination with a NIR light (wavelength = 905 nm). The net photocurrent and threshold voltage shift were gradually increased with the PODTPPD-BT content. The photosensitivity (S_P) and photoresponsivity (R_C) trend was almost proportional to the PODTPPD-BT content, but the S_P and R_C values at the lowest PODTPPD-BT content (10 wt%) were still ca. 55∼57% of those at 100 wt% (pristine PODTPPD-BT).