High Responsivity in Near-Infrared Phototransistor With Oriented Polymer Semiconductors

Near-infrared organic phototransistors (OPTs) in bottom-gated top-contact structures are being reported using an oriented p-type diketopyrrolopyrrole-based semiconducting polymer (SCP) (DPPT-TT). Here, highly oriented DPPT-TT floating films were prepared on a liquid substrate using the unidirectional floating-film transfer method (UFTM) and then utilized as the active layer. This innovative approach exhibits a dual-orientation advantage: They align polymer chains unidirectionally, enhancing charge transport along the backbone while simultaneously promoting an edge-on molecular arrangement relative to the substrate. This combination, coupled with highly uniform thin films, facilitates efficient charge transport pathways, contributing significantly to the fabrication of high-performance OPTs. Our DPPT-TT-based OPT exhibited a high field-effect mobility of 1.5 cm²·V⁻¹·s⁻¹ and photoresponsivity (R) > 10⁵ A·W⁻¹ at an intensity of 45 μW·cm⁻² under 810 nm light illumination. This exceptional performance is attributed to faster carrier transport and efficient charge collection in the oriented DPPT-TT films enabled by the UFTM.