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

Abstract

[Abstract]: Two fully non-fused small-molecule acceptors BTIC-1 and BTIC-2 are reportedfor application in near-infrared organic photodetectors (NIR OPDs). Bothacceptors contain the same conjugated backbone but differing sidechainregiochemistry, affording significant differences in their optical properties. Thehead-to-head arrangement of BTIC-2 results in a reduction of optical band gapof 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. Thesedifferences are rationalized on the basis of non-covalent intramolecularinteractions facilitating a more co-planar conformation for BTIC-2. OPDsbased 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 fullynon-fused small-molecule acceptors offer competitive device performance forNIR OPDs compared to fused-ring electron acceptors, but with reducedsynthetic complexity. Furthermore, the study presents an efficient strategy toenhance device performance by varying conformational locks.