Ultralow Voltage Floating Film Transferred DPP-DTT-Based Near-Infrared Phototransistor

In this article, we report water-processed polyvinyl alcohol (PVA) dielectric-based near-infrared (NIR) organic phototransistor (OPT) with operating voltage under <tex-math notation="LaTeX">$-$</tex-math> 1 V. For solution processing of organic semiconductor (OSC), we selected floating film transfer method (FTM) because of its large-area suitability and low-cost processing. The self-assembled film of poly2,5-(2-octyldodecyl)-3, 6-diketopyrrolopyrrole-alt-5,5-(2,5di(thien-2-yl)thieno 3,2-b-thiophene) (DPP-DTT) semiconducting layer was lifted from the surface of the water as liquid substrate. Thus, this NIR OPT has been fabricated by combining the advantages of using water-processed PVA dielectric and FTM-transferred DPP-DTT OSC layer from water as a substrate. The DPP-DTT NIR OPT shows a power sensitivity ( <tex-math notation="LaTeX">P)</tex-math> of 4.56 <tex-math notation="LaTeX">×</tex-math> 10 <tex-math notation="LaTeX">²</tex-math> (at 1.2 mW/cm <tex-math notation="LaTeX">²)</tex-math> , a responsivity of <tex-math notation="LaTeX">~</tex-math> 7.72 A/W, an external quantum efficiency (EQE) of <tex-math notation="LaTeX">~</tex-math> 1183.84%, and a detectivity of <tex-math notation="LaTeX">~</tex-math> 1.097 <tex-math notation="LaTeX">×</tex-math> 10 <tex-math notation="LaTeX">¹²</tex-math> Jones under <tex-math notation="LaTeX">-</tex-math> 1-V operation at the incident radiation of 850 nm (0.067 mW/cm <tex-math notation="LaTeX">²)</tex-math> . The maximum processing temperature in the whole experiment was not more than 100 <tex-math notation="LaTeX">^∘</tex-math> C. Analysis regarding threshold voltage shift and mobility on illumination has also been carried out, which shows a maximum threshold voltage shift of <tex-math notation="LaTeX">~</tex-math> 250 mV and 346% change in mobility at 1.2 mW/cm <tex-math notation="LaTeX">²</tex-math> (850 nm). A mechanism for performance enhancement using the trap charges (hydroxyl group) on the noncross-linked PVA dielectric has also been discussed.