Improved Thermally Activated Delayed Fluorescence-Based Electroluminescent Devices Using Vacuum-Processed Carbazole-Based Self-Assembled Monolayers

Interface engineering is a key aspect for high-performance organic light-emitting diodes (OLEDs). A comparative study between conventional conducting polymers (CPs) and carbazole-based self-assembled monolayers (SAMs) as hole-injection layers (HILs) is presented. A SAM enables an improved interface to achieve charge carrier balance and reduced interfacial recombination to enhance the external quantum efficiency (EQE) in OLEDs. An industry-compatible vacuum-processed SAM is reported for first time as a HIL in thermally activated delayed fluorescence (TADF)-based OLEDs. The deeper highest-occupied molecular orbital (HOMO: −5.3 eV) of this SAM enables efficient hole injection and reduces the leakage of current by ∼2 orders as compared to CP (HOMO: −5.00 eV) HIL-based OLEDs. Also, the built-in potential is reduced from 3.14 to 2.45 V, and the maximum EQE gets enhanced from 18.30% to 20.79% at the optimum thickness (6 nm) of the SAM. Furthermore, SAM-based OLEDs provide a 5-fold enhancement in operational stability, at 60% of the initial luminance, in comparison to CP-based OLEDs. This study is further extended to a blue TADF OLED, with similar findings.