Small-size graphene oxide (GO) as a hole injection layer for high-performance green phosphorescent organic light-emitting diodes

Abstract

In this work, we successfully synthesized small-size GO with the main size distribution at 200–400 nm using the tip sonication-assisted liquid-phase exfoliation method, which shows a suitable work function of 5.16 eV (annealing at 120 °C) well matching the ITO anode (4.80 eV) and extremely high transmittance (>98%, small size GO film spin-coated at 0.75 mg mL⁻¹ GO dispersion). Using small-size GO as hole injection materials, Ir(ppy)₃-based green phosphorescent organic light-emitting diodes (OLEDs) were demonstrated, and the resulting devices exhibit a lower turn-on voltage of 3.0 V than the PEDOT:PSS-based device (3.3 V). Further, the optimized GO-based OLED achieves maximum current efficiency, power efficiency, and external quantum efficiency reaching 73.14 cd A⁻¹, 53.95 lm W⁻¹, and 20.63%, respectively, which are significantly higher than the PEDOT:PSS-based reference device (68.82 cd A⁻¹, 48.04 lm W⁻¹, and 19.44%). It was demonstrated that effective holes injection capability and excellent film-forming properties for small-size GO guarantee the achievement of such high device performance. All relevant results indicate that the use of small-size GO as a hole injection material has great potential to alternative PEDOT:PSS in OLEDs.