Critical importance of the hole-transporter and emission layer interface for prolonging lifetime in a phosphor-sensitized hyper-OLED based on an MR-TADF emitter

Abstract

Multiresonance thermally activated delayed fluorescence (MR-TADF) technology has garnered significant attention because MR-TADF emitters enable both high efficiency and high color purity, making them ideal for next-generation high-resolution displays. However, the lifetime of MR-TADF-based OLEDs is considerably lower than that of phosphorescent and conventional TADF counterparts. To address this challenge, we focused on (i) a phosphor-sensitized hyper-OLED system to improve both the efficiency and the lifetime, and (ii) the interface between the hole-transport layer (HTL) and the emission layer (EML). This interface was found to be crucial for achieving both high efficiency and long operational lifetimes in MR-TADF-based hyper-OLEDs. By employing an HTL with a deep ionization potential, which prevents hole accumulation at the HTL/EML interface and direct carrier trapping on the MR-TADF emitter, we successfully extended the lifetime of phosphor-sensitized hyper-OLEDs based on MR-TADF emitters. Consequently, we realized green hyper-OLEDs with CIE coordinates of (0.31, 0.66), an external quantum efficiency of 28.1%, a power efficiency of 159.9 lm W⁻¹, and operational lifetimes at 95/90% of the initial luminance of 1000 cd m⁻² (LT_95/90) of over 600/2400 hours at a high brightness of 1000 cd m⁻². These performances are among the best reported in scientific literature.