Performance improvement of blue thermally activated delayed fluorescence OLEDs via vapor annealing by high boiling point solvent

In the study, the solution-processed PEDOT:PSS hole injection layer was treated by polar solvent vapor annealing (PSVA) to optimize the carrier transport and light extraction. The processing time and PEDOT:PSS film thickness both show a significant effect on the device performance. Treatment of 30 nm PEDOT:PSS for 45 min by DMSO and DMF vapor achieves the highest device performance. The EQE increases from 15.93% to 18.06% (by DMSO) and 20.02% (by DMF), respectively. The maximum luminance rises from 2150 cd/m2 to 3920 cd/m2 (by DMSO) and 5250 cd/m2 (by DMF). The AFM images and water contact angles demonstrate much larger roughness after PSVA treatment, which contributes to the higher light extraction efficiency by light scattering. The grazing incident X-ray small angle diffraction (GIXRD) pattern indicates a 110 orientation for DMF PSVA treated PEDOT: PSS, implying a more orderly molecular arrangement, which also enhances carrier transport in the corresponding PEDOT:PSS film. In general, the DMF SVA achieves higher device performance than the DMSO SVA. Finitedifference time-domain (FDTD) simulation denotes that the maximum radiation flux of the light field also increases together with more uniform distribution after PSVA treatment.