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 poly[2,5-(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 (
${P}$
) of
$4.56\,\, \boldsymbol {\times } \,\,10^{{2}}$
(at 1.2 mW/cm2), a responsivity of ~7.72 A/W, an external quantum efficiency (EQE) of ~1183.84%, and a detectivity of
$\boldsymbol {\sim } 1.097\,\, \boldsymbol {\times } \,\,10^{{12}}$
Jones under
$\boldsymbol {-}1$
-V operation at the incident radiation of 850 nm (0.067 mW/cm2). The maximum processing temperature in the whole experiment was not more than 100 °C. Analysis regarding threshold voltage shift and mobility on illumination has also been carried out, which shows a maximum threshold voltage shift of ~250 mV and 346% change in mobility at 1.2 mW/cm2 (850 nm). A mechanism for performance enhancement using the trap charges (hydroxyl group) on the noncross-linked PVA dielectric has also been discussed.