High-power-efficiency thermally activated delayed fluorescence white organic light-emitting diodes based on asymmetrical host engineering

Abstract

Developing thermally activated delayed fluorescence (TADF) white organic light emitting diodes (WOLED) featuring high power efficiencies faces a challenge in balancing carrier transport, energy transfer and quenching suppression. Here, we demonstrate that host matrix is crucial for the modification of optoelectronic process in emissive layers (EML) and the achievement of high power efficiency. Through asymmetrically introducing two or three diphenylphosphine oxide (DPPO) groups, three phosphine oxide (PO) hosts 24DBFDPO , 26DBFDPO and 248DBFTPO were constructed, in which dibenzofuran (DBF) chromophore is embedded by rationally spatial distribution of DPPO groups in 26DBFDPO and 248DBFTPO . Direct steric effect of DPPOs suppresses the host-dopant and dopant-dopant interaction induced quenching and mitigates excessive dopant-dopant energy transfer. Dually-doped white TADF films of 248DBFTPO reveal the improved white color purity with a high quantum yield of ~ 90%. Simultaneously, remote steric and electron-withdrawing effects of DPPOs remedy carrier transport in 248DBFTPO films. Based on a simple trilayer single-EML device structure, 248DBFTPO endowed its full-TADF WOLEDs with the state-of-the-art performance, especially the top-rank power efficiency beyond 70 lm W −1 . This work indicates host engineering can provide a feasible approach to realize the practical application of TADF daily lighting. • Host engineering based Asymmetric phosphine oxide hosts were implemented for white TADF diodes. • Intermolecular interactions in host matrixes are accurately adjusted with spatial asymmetry of phosphine oxide groups. • Carrier mobility of 10 −6 cm 2 V −1 s −1 for neat films and ~ 90% PLQYs of blue and white TADF doped films are achieved. • High power efficiency beyond 70 lm W −1 was realized by a simple trilayer single-emissive-layer TADF WOLED.