Toward Efficient and Metal-Free Emissive Devices: A Solution-Processed Host–Guest Light-Emitting Electrochemical Cell Featuring Thermally Activated Delayed Fluorescence

The next generation of emissive devices should preferably be efficient, low-cost, and environmentally sustainable, and as such utilize all electrically generated excitons (both singlets and triplets) for the light emission, while being free from rare metals such as iridium. Here, we report on a step toward this vision through the design, fabrication, and operation of a host–guest light-emitting electrochemical cell (LEC) featuring an organic thermally activated delayed fluorescence (TADF) guest that harvests both singlet and triplet excitons for the emission. The rare-metal-free active material also consists of a polymeric electrolyte and a polymeric compatibilizer for the facilitation of a cost-efficient and scalable solution-based fabrication, and for the use of air-stable electrodes. We report that such TADF-LEC devices can deliver uniform green light emission with a maximum luminance of 228 cd m –2 when driven by a constant-current density of 770 A m –2, and 760 cd m –2 during a voltage ramp, which represents a one-order-of-magnitude improvement in comparison to previous TADF-emitting LECs.