Spectral Stability Improvement by Controlling the Spatial Distribution of Excitons in Solution-processed Organic Light-emitting Diodes

The alternation of spatial exciton distribution in solution-processing organic light-emitting diodes (s-OLEDs) was exclusively studied by utilizing diffident types of host materials. The use of an n-type host material 2,2',2''-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) caused the electroluminescent spectral broadening accompanied with changing color coordinates upon applied voltage increase, which was being ascribed to the shift of the exciton density profile toward the hole transport layer. The extent of recombination zone shift was quantitatively examined in this study. Initially, under low luminance conditions, excitons were dispersed throughout the center of the EML. Sequentially, a large distance of 17 nm was expected for the recombination zone to shift to the interface with hole transport layer at a high voltage of 8 V. Alternatively, employing a p-type host material or a high mobility hole transport layer to prevent the overlap of recombination zone and mixing zone from happening is the way to effectively suppress this phenomenon.