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.

Automated summary

In this study, the solution-processed PEDOT:PSS hole injection layer was optimized for carrier transport and light extraction through polar solvent vapor annealing (PSVA). The processing time and PEDOT:PSS film thickness were found to significantly affect device performance. Treatment with DMSO and DMF vapor for 45 minutes resulted in the highest device performance, with an increase in EQE from 15.93% to 18.06% (by DMSO) and 20.02% (by DMF), as well as an increase in maximum luminance from 2150 cd/m2 to 3920 cd/m2 (by DMSO) and 5250 cd/m2 (by DMF). AFM images and water contact angles revealed higher roughness after PSVA treatment, contributing to enhanced light extraction efficiency through light scattering. Furthermore, GIXRD analysis showed a more orderly molecular arrangement in DMF PSVA treated PEDOT: PSS, leading to improved carrier transport in the film. Overall, DMF SVA demonstrated higher device performance compared to DMSO SVA, as validated by FDTD simulations showing increased radiation flux and more uniform distribution of the light field after PSVA treatment.