Developing sensitized green fluorescence for efficient, stable narrowband organic light emitting diodes

The thermally activated delayed fluorescence (TADF) or phosphorescence‐sensitized organic light‐emitting diodes (OLEDs) based on multi‐resonance TADF (MR‐TADF) emitters are greatly studied to develop an effective narrowband emitting system for wide color gamut display applications. However, developing pure green OLEDs to meet BT2020 and NTSC requirements is challenging. In this study, we investigated the TADF and phosphorescence‐sensitized OLEDs based on two green MR‐TADF final emitters, namely, BpIC‐DPA and BpIC‐Cz. The unique molecular structure of these emitters resulted in a pure green emission with narrow full width at half‐maximum (FWHM) and high PLQY in both solution and solid state. Notably, under optimal conditions, the BpIC‐Cz‐based OLEDs demonstrated a maximum external quantum efficiency (EQEmax) of 25.7% with alleviated efficiency roll‐off characteristics even at high luminescence (EQE5000 nits = 22.6%). The corresponding CIE coordinates are almost at the level of BT2020 and NTSC green‐color industrial standards. Additionally, the BpIC‐Cz‐based device displayed remarkable stability as seen by a noticeably longer device lifetime (LT90) of 25.3 h at a high initial luminance of 5000 nits. Achieving high EQE and longer device lifetime are crucial for OLEDs in real display applications. We investigated the process of sequentially optimizing a stable green phosphorescence‐sensitized OLED (PSF). In this work, a pure green emissive PSF‐OLED was fabricated and achieved a high EQE of 25.7% and a longer lifetime of 25.3 h at a high initial luminance of 5000 nits.