Remarkable Isomer Effect on the Performance of Fully Non‐Fused Non‐Fullerene Acceptors in Near‐Infrared Organic Photodetectors

Abstract Two fully non‐fused small‐molecule acceptors BTIC‐1 and BTIC‐2 are reported for application in near‐infrared organic photodetectors (NIR OPDs). Both acceptors contain the same conjugated backbone but differing sidechain regiochemistry, affording significant differences in their optical properties. The head‐to‐head arrangement of BTIC‐2 results in a reduction of optical band gap of 0.17 eV compared to BTIC‐1, which contains a head‐to‐tail arrangement, with absorption spanning the visible and near‐IR regions up to 900 nm. These differences are rationalized on the basis of non‐covalent intramolecular interactions facilitating a more co‐planar conformation for BTIC‐2. OPDs based on PM6:BTIC‐2 deliver a low dark current density of 2.4 × 10⁻⁷ A cm⁻², leading to a superior specific detectivity of 1.7 × 1011 Jones at 828 nm at ‐2 V. The optimized device exhibits an ultrafast photo response of 2.6 µs and a high ‐3 dB cut‐off frequency of 130 kHz. This work demonstrates that fully non‐fused small‐molecule acceptors offer competitive device performance for NIR OPDs compared to fused‐ring electron acceptors, but with reduced synthetic complexity. Furthermore, the study presents an efficient strategy to enhance device performance by varying conformational locks.