Solution-processed small molecule thin films and their light-emitting devices

Thin films of N,N′-bis-(3-Naphthyl)-N,N′-biphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB), tris-(8-hydroxyquinoline)-aluminum (Alq3) and their blends prepared by spin-coating process were investigated. Experimental results revealed that the NPB films prepared by spin-coating process have smoother surface than that of Alq3, which was attributed to their different molecular structures. Organic light-emitting devices (OLEDs) with emitting layer prepared by spin-coating the blends of NPB and Alq3 exhibited a maximum luminance and a current efficiency over 10,000 cd/m2 and 3.8 cd/A respectively, and when 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[l]benzopyrano[6,7,8-ij]quinolizin-11-one was doped in, a current efficiency of 8 cd/A can be obtained. Comparative device performance to the vapor-deposited OLEDs suggested that solution-process could be an alternative route for the fabrication of OLEDs based on Alq3.