Effect of PEDOT:PSS vs. MoO₃ as the hole injection layer on performance of C545T-based green electroluminescent light-emitting diodes

In order to understand the effect of hole injection on the performance of organic light-emitting diodes (OLEDs) with electron- and hole-type hosts used in the emissive layer, we fabricated OLEDs based on a green fluorescent 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1) benzopyropyrano(6,7-8-I,j)quinolizin-11-one (C545T) with poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and MoO₃ as the hole injection layer, respectively. Here, N,N′-di(naphthalene-1-yl) -N,N′-diphenyl-benzidine (NPB) and tris-(8-hydroxyquinoline) aluminum (Alq3) are, respectively, used as the host in the emissive layer for comparison. It is clearly found that different hole injection layers play different roles in the adjustment of the electron/hole injection and the transport balance, thus the different hosts are needed in the emissive layer for high electroluminescence efficiency OLEDs. This means that the selection of appropriate hole injection layers for OLEDs according to the different hosts in the emissive layer is especially important in the fabrication of high efficiency single emissive layer OLEDs.