Abstract High temperatures normally deteriorate the performance of light-emitting diodes, leading to excessive leakage currents, material degradation, and device failure. However, thermal activation is necessary for proper operation of OLEDs based on thermally-activated delayed fluorescence (TADF) compounds, where heat might be exploited as a side energy assisting electroluminescence. Here we show that performance of the TADF-based OLEDs can be significantly improved by heating, while extremely dependent on the applied biases. Enhancement of the OLED’s electroluminescence by 5-6 times is achieved when operating near the turn-on voltage and heating to 50 °C, but enhancement decreases at higher applied biases. At the same time, current characteristics reveal normal and abnormal regions, where currents increase and decrease with temperature, respectively. The discrepancy of temperature dependence of electroluminescence and current in the abnormal region provides improved external quantum efficiency and power efficiency of the device upon heating. These findings open up potential opportunities for exploitation of TADF-based OLEDs as energy upconverters pumping waste heat to light emissions.
Kuznetsova et al. (Tue,) studied this question.