Dramatic efficiency improvement in phosphorescent organic light-emitting diodes with ultraviolet-ozone treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

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Abstract
The treatment of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films by ultraviolet (UV) light-ozone to improve device efficiency was investigated utilizing two simple phosphorescent organic light-emitting diodes (PHOLEDs) architectures. The maximum external quantum efficiency in the first device increased from 3.5% for the untreated anode to 10.5%, while in the second device comprising an exciton blocking layer increased from 15.8% to 18.5%. The time dependence of the UV-ozone treatment on the performance was studied. The dramatic improvement in the PHOLED performance is attributed to the change in the PEDOT:PSS work function and more balanced charge injection, suggesting promising easy-to-do method to improve PHOLED performance.