Horizontal-oriented host materials enabled a deep-blue phosphor-sensitized OLED device with record 42% EQE

Researchers from the Changchun Institute of Applied Chemistry (CIAC), working with collaborators from the University of Science and Technology of China and Central China Normal University, developed a new deep-blue OLED device architecture that reaches an external quantum efficiency (EQE) of 42.0%, a record for this device class.

The OLED device is based on MR-TADF emitters, that combine high efficiency with narrowband, high-purity emission through fast exciton conversion. The researchers say that reaching over 40% EQE in this class has been difficult because most MR-TADF emitters have a low horizontal dipole ratio, which limits how much light can actually be extracted from the device.

To address this, the team designed a new horizontal-oriented host material, named 4CzTPS, built by symmetrically linking two bicarbazole units to a tetraphenylsilane core. The resulting linear molecular geometry naturally induces horizontal alignment on the substrate. The tetraphenylsilane core carries a strong positive electrostatic potential, which attracts the D1-DBN blue emitter (which carries a negative potential on its boron/nitrogen core) through electrostatic interaction. This pairing pushed the emitter's horizontal dipole ratio up to 94.5%, and the resulting phosphor-sensitized blue device reached 40.5% EQE.