Achieving ultra-high efficiency by tuning hole transport and carrier balance in fluorescent blue organic light-emitting diode with extremely simple structure

Ultra-high efficiency in fluorescent blue organic light-emitting diode (OLED) with extremely simple structure is demonstrated by tuning hole transport and carrier balance. Using 2-methyl-9,10-bis(naphthalen-2-yl)anthracene doped with 3 wt% 1-4-di-[4-(N,N-diphenyl)amino]styryl-benzene ([MADN: 3 wt%DSA-Ph]) as hole transport and emissive layer, the OLED gives sky-blue emission with 1931 Commission Internationale d'Eclairage color coordinates of (0.159, 0.281), luminous efficiency of 14.7 cd/A, power efficiency of 13.0 lm/W and external quantum efficiency of 10.0%. The efficiencies have been enhanced by 54.7% (11.4%), 49.4% (11.1%) and 38.9% (5.3%), respectively, in comparison with the counterpart having hole transport layer of NPB (MADN). Current versus voltage characteristics and impedance spectroscopy analysis of hole only cells elucidate that [MADN: 3 wt%DSA-Ph] shows reduced hole mobility as a result of trapping or scattering effect of DSA-Ph. Efficient hole injection and appropriate hole transport favorably tune holes entering into the emissive layer and improve carrier balance. Extra-fluorescent emission generated by triplet-triplet annihilation and broad emission zone by integrating hole transport and emission as a single layer are also responsible for ultra-high device efficiency.