High EQE and High Brightness Solution‐Processed TADF Light‐Emitting Transistors and OLEDs

Abstract Thermally activated delayed fluorescence (TADF) emitters can exhibit high quantum efficiencies by harvesting triplet excitons through efficient reverse intersystem crossing. Reports on efficient TADF based light‐emitting field‐effect transistors (LEFETs) are rare. Moreover, despite efficient TADF organic light‐emitting diodes (OLEDs), most devices have thermally evaporated multilayer device designs. In this work, highly efficient solution processed LEFETs using ACRXTN [3‐(9,9‐dimethylacridin‐10(9H)‐yl)‐9H‐xanthen‐9‐one] are demonstrated to show high external quantum efficiencies (EQEs) of ≈1% and on/off ratios (≈10⁵) at low operating voltages (≈22 V) with negligible EQE roll‐off even at ≈1,500 cd m^–2. The same emitter is further studied in solution‐processedOLEDs with a simple architecture to achieve high peak EQEs (≈16%) and brightness (>1000 cd m^–2). The OLEDs retain a high EQE (≈10%) at 20 000 cd m^–2, indicating excellent charge balance even with such simple device architecture. Our optical simulations identify EQE discrepancy in the two devices, mainly arisen from a poorer light out‐coupling efficiency in the LEFETs (0.8%) than that (≈24%) in the OLEDs. This work shows state‐of‐the‐art of solution‐processed TADF LEFETs and OLEDs with simple device architectures and negligible EQE roll‐off.