Flexible near-infrared (NIR) organic light-emitting diodes (OLEDs) face efficiency challenges due to low photoluminescence quantum yields (PLQYs) in NIR emitters, governed by the energy gap law. Accelerating radiative transitions via the Purcell effect in optical microcavities offers a solution, but conventional flexible semitransparent electrodes struggle to balance microcavity-enhanced PLQY and light outcoupling efficiency (OCE). We address this with a micro-structured magnesium-bismuth (Mg-Bi) alloy electrode offering 40% broadband transmittance (400-1600 nm) and conductivity (29.3 Ω ◻-1). The alloy's low real permittivity supports less confined surface plasmon polariton and, with a capping layer, yields 60% NIR transmittance in an organic-to-air optical configuration. This design achieves 42.3% OCE and elevates the PLQY of a 704 nm NIR emitter to 71.8%, enabling flexible NIR-OLEDs with a record 24.3% external quantum efficiency. The synergy of optical engineering and conductive microstructures establishes a universal strategy for high-efficiency flexible NIR optoelectronics.
Xu et al. (Thu,) studied this question.