Phosphor

Narrowband

Green-light

Full width at half maximum

Materials science

Layer (electronics)

Electroluminescence

Full color

Physics

Quantum efficiency

Nanotechnology

Optics

Blue light

OLED

Luminance

Optoelectronics

Advanced Optical Materials

Thermally activated delayed fluorescence (TADF) materials that are able to realize electroluminescence showing simultaneously narrow emission band, high color purity, and high efficiency are highly demanded for display applications. Up to now, a few blue emissive TADF materials with such characteristics have been reported, while green TADF materials with such features are extremely scarce. Herein, two TADF compounds with highly efficient narrowband bluish green/green emission (full-width at half-maximum (FWHM): 22 and 21 nm in toluene) induced by multiple resonance effect are reported. An optimized organic light-emitting diode based on the green emissive compound shows a fairly narrow electroluminescent spectrum (FWHM: 33 nm), as well as an excellent color purity with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.20, 0.65), which is a close resemblance to the standard green-light CIE coordinates of (0.21, 0.71) defined by the National Television System Committee. Meanwhile, the maximum external quantum efficiency (EQE) up to 25.5% is achieved and a high EQE of 20.1% is maintained at a practical high luminance of 1000 cd m−2. The outstanding device performance of the compound makes it attractive for potential practical applications.

Molecular‐Structure and Device‐Configuration Optimizations toward Highly Efficient Green Electroluminescence with Narrowband Emission and High Color Purity