Design of ultranarrow-bandgap acceptors for efficient organic photovoltaic cells and highly sensitive organic photodetectors

The fabrication of multifunctional electronic devices based on the intriguing natures of organic semiconductors is crucial for organic electronics. Ultranarrow-bandgap materials are in urgent demand for fabricating high-performance organic photovoltaic (OPV) cells and highly sensitive near-infrared organic photodetectors (OPDs). By combining alkoxy modification and an asymmetric strategy, three narrow-bandgap electronic acceptors (BTP-4F, DO-4F, and QO-4F) were synthesized with finely tuned molecular electrostatic potential (ESP) distributions. Through the careful modulation of electronic configurations, the optical absorption onsets of DO-4F and QO-4F exceeded 1 μm. The experimental and theoretical results suggest that the small ESP of QO-4F is beneficial for achieving a low nonradiative voltage loss, while the large ESP of BTP-4F can help obtain high exciton dissociation efficiency. By contrast, the asymmetric acceptor DO-4F with a moderate ESP possesses balanced voltage loss and exciton dissociation, yielding the best power conversion efficiency of 13.6% in the OPV cells. OPDs were also fabricated based on the combination of PBDB-T:DO-4F, and the as-fabricated device outputs a high shot-noise-limited specific detectivity of 3.05 × 1013 Jones at 850 nm, which is a very good result for near-infrared OPDs. This work is anticipated to provide a rational way of designing high-performance ultranarrow-bandgap organic semiconductors by modulating the molecular ESP.