Conjugated Polymer Heteroatom Engineering Enables High Detectivity Symmetric Ambipolar Phototransistors.

Solution-processed high-performing ambipolar organic phototransistors (OPTs) can enable low-cost integrated circuits. Here, we demonstrate a heteroatom engineering approach to modify the electron affinity of a low band gap diketopyrrolopyrole (DPP) co-polymer, resulting in well-balanced charge transport, a more preferential edge-on orientation and higher crystallinity. Changing the comonomer heteroatom from sulfur (benzothiadiazole (BT)) to oxygen (benzooxadiazole (BO)) led to an increased electron affinity and introduced higher ambipolarity. Organic thin film transistors fabricated from the novel PDPP-BO exhibited charge carrier mobility of 0.6 and 0.3 cm2/Vs for electrons and holes, respectively. Due to the high sensitivity of the PDPP-based material and the balanced transport in PDPP-BO, we present its application as an NIR detector in the device architecture of organic phototransistors. By maintaining a high on/off ratio (9 × 104), we show ambipolar OPTs with photoresponsivity of 69 and 99 A/W and specific detectivity of 8 × 107 for the p-type operation and 4 × 109 Jones for the n-type regime. The high symmetric NIR-ambipolar OPTs were also evaluated as ambipolar photo-inverters, and showed a 46% gain enhancement under illumination. This article is protected by copyright. All rights reserved.