Efficient all-fluorescence white organic light-emitting diodes with superior color stability and low efficiency roll-off employing matrix-free blue emitting layers

All-fluorescence white organic light-emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) have great potential for large-area light sources. However, designing all-fluorescence WOLEDs that can simultaneously achieve high efficiency, low efficiency roll-off, and excellent color stability with simplified device architectures is still challenging. Herein, we report a simplified three-color all-fluorescence WOLED comprising a matrix-free TADF blue emitting layer (EML) and sensitized EMLs. By broadening exciton distribution and reducing exciton losses through multiple sensitizing processes using an advanced triple-EML configuration, we simultaneously improve the color stability and reduce the efficiency roll-off of DMAC-DPS-based all-fluorescence WOLEDs. Moreover, by introducing a blue emitter Cz-TRZ3 to enhance the charge balance, the all-fluorescence WOLED reaches a maximum external quantum efficiency (EQE) of 24.3% and maintains 22.4% and 19.6% at 100 and 1000 cd m-2, respectively. Remarkably, the device shows extremely color stable electroluminescence spectra with a negligible chromaticity coordinate shift of (0.001, 0.004) in a wide luminance range of 1000-10 000 cd m-2. Our results provide a universal strategy to achieve all-fluorescence WOLEDs with low efficiency roll-off and superior color stability. All-fluorescence WOLEDs comprising a matrix-free TADF blue emitting layer simultaneously reach low efficiency roll-off and extremely color stable electroluminescence spectra.