Novel A–D–A Fused‐Ring Semiconducting Small Molecules Featuring a Strong Electron‐Donating Indolo[3,2‐b]indole Core for Efficient Short‐Wavelength Infrared Organic Light‐Emitting Diodes

ABSTRACT

Short‐wave infrared (SWIR) organic light‐emitting diodes (OLEDs) have received intense attention, owing to rapid progress in their applications in biomedicine and optoelectronics, although their electroluminescence (EL) efficiency is still far from unity. Recently, various fluorescent acceptor–donor–acceptor (A–D–A) type aromatic fused‐ring non‐fullerene acceptors have demonstrated effective suppression of non‐radiative losses in organic photovoltaics, rendering them promising candidates for SWIR OLEDs. Nevertheless, SWIR fluorescent emitters remain scarce in terms of molecular structure diversity, and state‐of‐the‐art SWIR OLEDs are still limited by relatively low radiative efficiency, unbalanced injection and transport of charge carriers, and light out‐coupling efficiency. In this study, we report high‐performance SWIR OLEDs from a novel A–D–A molecule, named DNIC, in which the traditional carbazole moiety is replaced with an indolo[3,2‐b]indole moiety as a strong electron‐donating group. Owing to enhanced intramolecular charge transfer arising from the multiple donor‐acceptor (D–A) effect within the conjugated backbone, DNIC possesses a narrow optical bandgap of 1.22 eV. By doping DNIC into a near infrared (NIR) emitter Y11, we achieve a maximum external quantum efficiency (EQE) of 0.023% for EL with an emission peak at 1071 nm, outperforming the neat film‐based devices (0.010%) and thus placing it among the best SWIR OLEDs reported to date.