Efficient solution-processed fluorescent OLEDs realized by removing charge trapping emission loss of BODIPY fluorochrome†

The thermally activated delayed fluorescence (TADF)-sensitized fluorescent (TSF) dye strategy has been used successfully in thermally evaporated organic light-emitting diodes (eOLEDs), but the development of solution-processed TSF-OLEDs (TSF-sOLEDs) is still very limited to date. Previously, the introduction of electronically inert shielding terminal groups for TADF sensitizer and/or fluorescent dyes was commonly used in TSF-sOLEDs, which aimed to achieve sufficient Förster energy transfer (FET) while restraining notorious Dexter energy transfer (DET) at a high doping concentration of fluorescent dyes. However, this approach has not yet enabled efficient TSF-sOLEDs owing to severe charge trapping emission (CTE) for triplet loss. In this study, by simply utilizing highly efficient boron-dipyrromethene derivatives (BODIPYs) that simultaneously feature high fluorescent quantum efficiency and narrow-band emission spectra, we developed highly efficient and super color-purity TSF-sOLEDs using a 0.1 wt% ultralow doping strategy. As confirmed, the resultant ultralow doping TSF-sOLEDs achieved sufficient FET from sensitizer to fluorochrome without noticeable CTE issues. The device achieves record maximum external quantum efficiency (EQE_max) and current efficiency (CE_max) of 21.5% and 78.8 cd A⁻¹, respectively, and an ultrapure green emission with Commission International de l’Eclairage (CIE) coordinates of (0.28, 0.65). This study validates the new device architecture of ultralow doping TSF-sOLEDs, which paves the way for future development of high-resolution TSF-sOLED displays via a simple solution-processed manufacturing approach.