Enabling High-Efficiency Organic Light-Emitting Diode with Trifunctional Solution-Processable Copper(I) Thiocyanate

We report on a low-temperature solution processed trifunctional inorganic p-type semiconductor, copper(I) thiocyanate (CuSCN), as a hole injection/transporting and electron-blocking layer for high-efficiency organic light-emitting diodes (OLEDs). The electroluminescence (EL) characteristics of CuSCN and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) based devices were studied with the structure of 4,4'-bis(N-carbazolyl)-1,1'-biphenyl as the host, bis[2-(2-pyridinyl-N)-phenyl-C] (acetylacetonato) iridium (III) [(ppy)(2)Ir(acac)] as the green emitter, 2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) as the electron transporting layer, and lithium fluoride/aluminum as the cathode electrode. The power efficacies for the CuSCN based devices are found to be 51.7 and 40.3 lm/W at 100 and 1000 cd/m(2), respectively, which are 13 and 60% higher than the PEDOT:PSS based counterparts. These are the highest power efficacies ever reported for this particular device architecture. The superior EL characteristics may be explained by its unique electronic properties. We believe that the high lowest unoccupied molecular orbital (-1.8 eV) and deep highest occupied molecular orbital (-5.5 eV) of CuSCN assist to confine the electron injected into the emission layer and facilitate the injection of hole, likewise enhancing recombination. The present study will serve to enable highly efficient white OLEDs for general lighting purposes.