Crosslinkable hole-transporting small molecule as a mixed host for efficient solution-processed red organic light emitting diodes

The fabrication of multilayer organic light-emitting diodes through solution processing presents numerous challenges, primarily concerning dissolution of the first layer during deposition of a second layer. Here, we demonstrate a highly efficient solution processed red organic light emitting diode utilizing an electron confining cross linkable small molecule, 9,9′-bis(4-vinylphenylmethylen)[3,3′]bi-carbazole, as a hole transporting and co-host material. Compared with the corresponding single host device, the luminance of the mixed host device is enhanced from 8351 cd m−2 to 15,200 cd m−2, an increment of 82%, in addition, power efficiency and current efficiency also show an increment of 25% and 20% at 100 cd m−2, respectively. Results show that use of the crosslinking material makes the hole injecting, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), layer more intact during the deposition of the emissive layer which improves the film quality and hence device brightness. The enhanced charge carrier balance and broadened exciton recombination zone due to the mixed host contribute to the improvement of efficiency and efficiency roll-off.