White-light-emitting organic electroluminescent devices with poly-TPD as emitting layer

We report a method to achieve white organic light-emitting diodes (WOLEDs) with poly {N,N′-bis (4-butylphenyl)-N,N′-bis(phenyl)-benzidine} (poly-TPD) as single emitting layer. Monomer emission, excimer and electromer emission are all observed from poly-TPD, and combining them the white light emission with color coordinate of Commission International de L’Eclairage (CIE) (0.37, 0.31) was achieved. Double electron transport layer with apposite thickness 1,3,5-tris(1-phenyl-1H-benzimida-zol-2-yl) benzene (TPBi) (30 nm) and tris(8-hydroxyquinolato) aluminum (Alq3) (20 nm) were introduced to improve the performance of WOLEDs. The brightness reached 1000 cd/m2 at 22 V with an efficiency of 1.0 cd/A.