Multi-Sensitization Strategy for High Efficiency and Low Efficiency Roll-off Solution-Processed Single-Emission-Layer All-Fluorescence White Organic Light-Emitting Diodes.

A multi-sensitization strategy is proposed to develop highly efficient and low efficiency roll-off solution-processed single-emission-layer all-fluorescence white organic light-emitting diodes, resulting in significantly boosted Förster energy transfer from blue emitter and green sensitizer to the orange-red dopant and thus a recorded external quantum efficiency of 22.8%. [Display omitted] • Multi-sensitization strategy to boost FRET and block exciton loss. • Exciton utilization efficiency was improved by BDP-C-Cz with HLCT character. • An EQE of 26.8% for blue s-OLED was achieved with 70% Θ// of spin-coated EML. • An EQE of 22.8% was achieved for the multi-sensitized all-fluorescence s-WOLED. Limited by the inefficient energy transfer from blue thermally activated delayed fluorescence (TADF) material to the complementary color fluorescent dopant and unwanted charge trapping effect, it is challenging to achieve a spectrally stable, high efficiency and low efficiency roll-off solution-processed single-emission-layer (SEL) white organic light-emitting diodes (WOLEDs). Herein, a highly efficient solution-processed all-fluorescence SEL-WOLED with suppressed efficiency roll-off and stable electroluminescence spectra is achieved by introducing a hybridized local and charge-transfer (HLCT) orange-red emitter (BDP-C-Cz) and a TADF sensitizer (4CziPN) into an optimized blue TADF OLED. Specially, the adopted BDP-C-Cz emitter has a high molar absorption coefficient, whose absorption spectrum has a significant overlap with the emission spectra of 4CziPN and blue emitter. By additionally introducing 4CziPN as an assistant sensitizer of blue emitter, Förster energy transfer can be enhanced to give favorable exciton allocation and thus effectively blocks triplet exciton loss. Accordingly, a recorded external quantum efficiency of 22.8% and current efficiency of 60.0 cd/A were realized for the solution-processed SEL-WOLEDs, with color coordinates of (0.33, 0.44) and good color stability, providing a valuable guidance for the future development of simplified, high-efficiency and low-cost WOLEDs. [ABSTRACT FROM AUTHOR]