High-efficiency low-voltage stable inverted transparent electrophosphorescent organic light-emitting diodes: combining electrically doped carrier transport layers and iridium-complex doped emissive layer

Abstract

We demonstrated high-efficiency low-voltage stable inverted transparent clectrophosphorescent organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode. The structure contains an iridium-complex doped emissive layer sandwiched in between n- and p-doped charge transport layer with appropriate blocking layers to form a nip structure. The devices are about 50% transparent and emit green light from both sides with peak external quantum efficiency (EQE) of 4.08% (14.3 cd/A). At 100 cd/m 2 , the EQE is 2.8% (13 cd/A) at an operating voltage of 4.3 V. The devices exhibit a lifetime of above 50 hours under continuous constant-current driving for the initial luminance of about 9000 cd/m 2 in vacuum, which project a lifetime of ∼5000 hours for 100 cd/m 2 .