Doubling the efficiency of solution-processed blue phosphorescent organic light-emitting diodes via modified PEDOT : PSS hole-injection layers

Abstract

For solution-processed organic light-emitting diodes (OLEDs), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS) is commonly utilized as the hole injection layer due to its superior conductivity, transparency, and excellent film-forming properties. Compared to the excellent performance of red and green OLEDs, low efficiency in blue OLEDs is the bottleneck because of the large hole injection barrier caused by the wide bandgap of blue phosphorescent materials and their mismatched energy levels with PEDOT : PSS. To optimize device performance, a simple and cost-effective strategy was devised by incorporating various dopants such as PSSA, PSSNa, and PSSNH₄ into PEDOT : PSS films. Due to the formation of the PSS layer and the promotion of conduction via cationic carriers, coupled with the utilization of the exciplex as the host, the optimal device exhibited the maximum external quantum efficiency (EQE) of 21.33%, nearly doubling the efficiency of the original device (11.88%). The turn-on voltage was reduced from approximately 3.9 V to about 3.5 V. Additionally, the FIrpic-based blue phosphorescent device achieved the maximum EQE of up to 24.18%, which, to the best of our knowledge, represents the highest value recorded for solution-processed OLEDs based on FIrpic.