Thermal Enhancement of TADF‐OLED Performance: Size of Active Area Matters

ABSTRACT Temperature significantly impacts the performance of light‐emitting diodes, typically causing degradation as they heat up. However, OLEDs using thermally activated delayed fluorescence (TADF) emitters show a remarkable increase in electroluminescence up to one order of magnitude, depending on the applied voltage, as temperature climbs from 18 to 50°C. This work reveals that this heat‐induced boost in TADF‐OLED performance is also influenced by the device's active area. By varying the active area from 225 to 4 mm 2 , we show that the thermal enhancement in both electroluminescence and external quantum efficiency (EQE) noticeably declines in smaller devices, with the smallest device showing performance deterioration at high temperatures. While large‐area devices demonstrate up to a tenfold increase in EQE near the turn‐on voltage due to heating, their EQE remains low compared to smaller devices, with heat only partially bridging this gap. The size‐dependent behaviour is linked to factors like interface non‐uniformity and aging in large areas, making these devices prone to burnouts that further worsen with thermal runaway. Since OLED performance often decreases with larger sizes, the ability of heating to mitigate this effect supports the effective use of large displays at higher temperatures and suggests TADF‐OLEDs can convert waste heat into light efficiently.