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 $-$ 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 ( $\textit{P}\text{)}$ of 4.56 $\bm{\times} $ 10 $^{\text{2}}$ (at 1.2 mW/cm $^{\text{2}}\text{)}$ , a responsivity of $\bm{\sim}$ 7.72 A/W, an external quantum efficiency (EQE) of $\bm{\sim}$ 1183.84%, and a detectivity of $\bm{\sim}$ 1.097 $\bm{\times} $ 10 $^{\text{12}}$ Jones under $\bm{-}$ 1-V operation at the incident radiation of 850 nm (0.067 mW/cm $^{\text{2}}\text{)}$ . The maximum processing temperature in the whole experiment was not more than 100 $^\circ$ C. Analysis regarding threshold voltage shift and mobility on illumination has also been carried out, which shows a maximum threshold voltage shift of $\bm{\sim}$ 250 mV and 346% change in mobility at 1.2 mW/cm $^{\text{2}}$ (850 nm). A mechanism for performance enhancement using the trap charges (hydroxyl group) on the noncross-linked PVA dielectric has also been discussed.