Versatile Host Materials for Both D–A‐Type and Multi‐Resonance TADF Emitters toward Solution‐Processed OLEDs with Nearly 30% EQE

Abstract Fabricating solution‐processible host material for thermally activated delayed fluorescence (TADF) emitter remains a formidable challenge for organic light‐emitting diodes (OLEDs). In this work, two new host materials, namely 3CzAcPy and 9CzAcPy, are found to exhibit high triplet energy levels, high thermal stability, and excellent film morphology from a solution process. An in‐depth analysis on the photophysical data and device performance reveals the isomeric effect of the host materials has a significant impact not only on the host properties, but also on the host–dopant interactions and thus the performance of the resulting solution‐processed TADF OLEDs. Impressively, the new hosts are proven to be suitable for both donor–acceptor type and multi‐resonance TADF emitters, achieving state‐of‐the‐art device performance. By using the new host 9CzAcPy, solution‐processed OLED based on a donor–acceptor TADF emitter of DPAC‐PCN, a maximum external quantum efficiency (EQE) of 29.5% is achieved, and solution‐processed narrowband OLED based on a multiple‐resonance TADF emitter of BN‐CP1 acquires a maximum EQE of 26.6%. These efficiencies represent the highest values among the solution‐processed TADF OLEDs. This study highlights the significance of host–dopant interactions in modulating the electroluminescence performance of TADF emitters, and provides an effective design principle for solution‐processible host materials.