Recombination Zone Control without Sensing Layer and the Exciton Confinement in Green Phosphorescent OLEDs by Excluding Interface Energy Transfer

Abstract

We report the confinement of recombination zone (RZ) in green phosphorescent organic light-emitting diodes (Ph-OLEDs) for enhanced efficiency by varying the emission layer (EML) thickness and through quantum well (QW) insertion. At low thickness of EML, the efficiency is reduced owing to the diffusion of the RZ toward the EML/hole transport layer interface, which was revealed through the presence of exciton blocking layer [TCTA: tris(4-carbazoyl-9-ylphenyl)amine] excitation accompanied by a blue-shift in electroluminescence (EL). Further increase in the thickness of the EML caused the RZ to move toward the cathode, which was determined based on the disappearance of TCTA emission and the corresponding red-shift observed in EL spectra. The solid-state and time-resolved area normalized photoluminescence emission spectra investigations further corroborate the RZ movement tactics along with TCTA excimer generation and exciplex generation between TCTA and tris[2-phenylpyridinato-C2,N]iridium(III) Ir(ppy)3. The ...