Improving the luminous efficiency of red organic light-emitting diodes using a carrier balance layer

This work proposes a carrier balance layer (CBL) to yield red organic light-emitting diodes (OLEDs) with high luminous efficiency. In the structure of OLEDs, the CBL (1,3,5- tris(N-phenylbenzimidazol-2,yl) benzene, TPBi) is inserted into the emitting layer, 4-(dicyanomethylene)-2-t- butyl-6(1,1,7,7-tetra-methy-]julolidyl-9-enyl)-4H-pyran (DCJTB)-doped tris(8-hydroxyquinolino) -aluminum)-(Alq(3)). Experimental results demonstrated that the luminous efficiency of the OLED with a CBL was 4.63 cd/A 30% higher than that of the typical OLED without a CBL. Inserting CBL into an emitting layer is suggested to rearrange and enlarge the recombination zone. The improvement in efficiency is attributed to the enlargement of the recombination zone in which more excitons were generated and recombined. Sufficient electron-hole recombination improved luminous efficiency. (c) 2006 The Electrochemical Society.