• Energy Research

AbstractSolution‐processed high‐performing ambipolar organic phototransistors (OPTs) can enable low‐cost integrated circuits. Here, 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, is demonstrated. Changing the comonomer heteroatom from sulfur (benzothiadiazole (BT)) to oxygen (benzooxadiazole (BO)) leads to an increased electron affinity and introduces higher ambipolarity. Organic thin film transistors fabricated from the novel PDPP‐BO exhibit charge carrier mobility of 0.6 and 0.3 cm2 Vs⁻1 for electrons and holes, respectively. Due to the high sensitivity of the PDPP‐based material and the balanced transport in PDPP‐BO, its application as an NIR detector in an OPT architecture is presented. By maintaining a high on/off ratio (9 × 104), ambipolar OPTs are shown with photoresponsivity of 69 and 99 A W⁻1 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 are also evaluated as ambipolar photo‐inverters, and show a 46% gain enhancement under illumination.

The performance of organic photodetectors (OPDs) using conjugated polymer donors and molecular acceptors has improved rapidly, but many polymers are difficult to upscale due to their complex structures. This study examines two low-complexity thiophene copolymers with substituted benzooxadiazole (FO6-BO-T) or benzothiadiazole (FO6-T). Substituting sulfur with oxygen in FO6-BO-T increased its ionization energy without affecting the optical gap. When blended with the nonfullerene acceptor IDSe, FO6-BO-T showed a significantly lower dark current density (2.06·10-9 A cm-2 at -2 V) compared to FO6-T. Grazing incidence wide-angle X-ray scattering (GIWAXS) measurements demonstrated that pristine FO6-BO-T exhibited a more ordered morphology than FO6-T. However, blending resulted in a significant disruption to the ordered domains in both cases, with a loss of orientational order, suggesting that FO6-BO-T's improved performance is largely related to its increased ionization energy. This study demonstrates the potential of chalcogen atom engineering to enhance the performance of the OPD in scalable polymers.