Improved Efficiency, Stable Spectra and Low Efficiency Roll-off Achieved Simultaneously in White Phosphorescent Organic Light-Emitting Diodes by Strategic Exciton Management

Despite their merits of high efficiency and environmental friendliness, phosphor based white organic light-emitting diodes (WOLEDs) for commercial applications still face tough challenges of efficiency roll-off and color stability. Herein, we fabricated high-efficiency phosphor WOLEDs with extremely low roll-off and stable white emission by employing mixed spacer layer between the two complementary emissions as well as mixed host in the orange layer. The strategic exciton management in our proposed device structure greatly balanced the transport of charge carriers due to the excellent exciton manipulation of the mixed spacer, and significantly suppressed the exciton quenching owing to the extended exciton recombination region, which significantly minimized the efficiency roll-off of the fabricated WOLEDs. The resulting phosphor WOLED exhibited the maximum current efficiency (CE) and power efficiency (PE) of 47.5 cd A(-1) and 44.7 lm W-1, respectively, and the CE still had 43.1 cd A(-1) at 5000 cd m(-2), showing a suppressed efficiency roll-off of only 9.2%. Additionally, the device achieved fairly stable spectra over a wide range of luminance with suitable CIE coordinates for indoor lighting and outdoor displays.