Optimizing QLED Performance and Stability via the Surface Modification of PEDOT:PSS Experimental Insights and DFT Calculations

The presence of the acidic and weak ionic conductor polystyrenesulfonate (PSS) in poly(3,4-ethylenedioxythiophene:PSS (PEDOT:PSS) leads to degradation and limits the charge transfer within quantum dot light-emitting diodes (QLEDs). Two-step solvent treatment resulted in a 40% reduction of PSS, which could be attributed to ethylene glycol (EG) attenuating the ionic interactions between PSS and PEDOT via interacting with PSS through hydrogen bonding. Methanol dissolved the predominant PSS and EG from the surface. The redshift of the peak representing the symmetrical vibration of Cα═Cβ in the Raman spectrum confirmed the conformation of benzoid structure to quinoid structure after the surface treatment. This conformation was attributed to the extension of the conjugation length and the reduction of the energy barrier within the PEDOT chain. This resulted in the improved conductivity and charge hopping of the PEDOT:PSS, which was also proven using density functional theory (DFT) calculations. Reducing the insulating and acidic PSS improved the electroluminescence performance and extended the operational lifetime of the QLEDs. The tris(dimethylamino)phosphine-based InP QLEDs exhibited an external quantum efficiency (EQE) of 6.4%, that value is comparable to those of tris(trimethylsilyl)phosphine-based QLEDs, and operational lifetime (T₅₀) of 125.6 h.