A Brief Overview of Thermally Activated Delayed Fluorescence (TADF) Light Emitting Electrochemical Cells (LEECs)

Thermally Activated Delayed Fluorescence Light-Emitting Electrochemical Cells (TADF-LEECs) are single-layer emitters in which the active film contains both a luminophore and mobile ions (either an ionic TADF emitter or a neutral TADF host mixed with a salt/ionic complex). Under bias voltage, the ions migrate and form electrical double layers (EDLs) at the electrodes, lowering the injection barriers. Subsequent electrochemical doping (p-type near the anode, n-type near the cathode) creates a dynamic p-i-n junction with radiative recombination inside the film. The TADF mechanism- a small ΔEₛₜ that enables thermally driven reverse intersystem crossing (rISC), allows the harvesting of singlet and triplet excitons without heavy metals, which in principle enables an internal quantum efficiency close to unity. Compared to multilayer OLEDs, TADF-LEECs offer a simpler architecture, fully solution-based fabrication compatible with print/roll, air-stable electrodes, and straightforward color tuning via the composition of the mixed layer. Remaining challenges include turn-on delay (ion migration), operational stability/lifetime and aggregation/dexter-type quenching at high doping levels. Effective design therefore targets high PLQY of the film, small ΔEST, controlled ionic conductivity, rigid matrix with appropriate Tg, and appropriate alignment of energy levels in host-guest systems.