High-quality all-fluorescent white organic light-emitting diodes obtained by balancing carriers with hole limit layer

Broad-spectrum white organic light-emitting diodes (WOLEDs) based on all-fluorescent materials with excellent color stability were realized by precisely optimizing the doping concentrations of guests and the thickness of each functional layer. High-efficiency blue fluorescent emissive material 9,10-bis[4-(6-methylbenzothiazol-2-yl)phenyl]anthracene (DBzA) was selected as blue emitter and doped into first light emitting layer (EML), while red-emitting dopant 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidn-4-yl-vinyl)- 4H-pyran (DCJTB) was doped into green-emitting host material tris(8-hydroxyquinoline) aluminum (Alq3) as the second EML. Thin hole limit layer (HLL) was inserted to balance carriers' distribution within the two EMLs and to modulate the luminous intensity ratio of different emissions. Finally, the optimal WOLED exhibited the maximum current efficiency of 9.34 cd/A, power efficiency of 10.06 lm/W, brightness up to 29,364 cd/m2 and turn-on voltage of only 2.7 V. In addition, this device displayed stable Commission International de I'Eclairage coordinates from (0.339, 0.382) to (0.324, 0.354) with increasing current density. The highest color rendering index and corresponding correlated color temperature reach 85 and 5492 K, respectively, and the T50 lifetime reaches 7912 h. The achievement of these results fully exhibits the effectiveness of the HLL in improving spectral stability and operation lifetime.