ORGANIC LIGHT-EMITTING DEVICES WITH QUANTUM WELL STRUCTURES USING CARBAZOLE DERIVATIVE 4CZTPN-PH AS AN EMITTING MATERIAL

Herein, we investigate the electroluminescent properties of organic light-emitting diodes (OLEDs) based on a carbazole derivative 2,3,5,6-tetrakis(3,6-diphenyl-9H-carbazol-9-yl)-1,4-benzenedicarbonitrile (4CzTPN-Ph) with red emission.Two types of OLEDs were fabricated using this emitter: the first employed a host-guest system, while the second utilized a light-emitting structure with a triple cascade of quantum wells.In the second OLED, an ultrathin 4CzTPN-Ph emitter layer with 5 nm thickness was placed between the layers of 3,3-di(9H-carbazol-9-yl)-1,1-biphenyl (mCBP) and diphenyl [4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1) forming the first well, and between the same type of TSPO1 layers in the second and third quantum wells.This configuration made it possible to create optimal energy barriers at the interfaces to scatter charge carriers and excitons within each well efficiently.This configuration also contributed to expanding the carrier recombination zone and reducing the exciton quenching probability.Discrete energy levels for electrons and holes in the quantum wells were calculated by solving the stationary Schrdinger equation in the frequency domain.The calculations showed the localization of electrons and holes in the corresponding quantum wells.A comparative analysis of the efficiency of OLED devices (brightness, power efficiency, and current efficiency) showed that in the first type of OLED, efficient energy transfer to the 4CzTPN-Ph emitter was achieved due to the relatively broad spectral overlap between the emission spectrum of the host component (mCBP) and the absorption spectrum of the 4CzTPN-Ph emitter.As a result, the OLED with the host-guest system achieved an external quantum efficiency of 2% at a maximum brightness of more than 1000 cd/m.While the second type of device demonstrated slightly lower efficiency, the advantage of the quantum wells cascade structure lies in its narrow quantum wells (5 nm), which result in a characteristic narrowing of the electroluminescence spectra.This produces spectrally purer red emission with International Commission on Illumination (CIE) coordinates of (0.58, 0.33), compared to the broader spectrum of the doped OLED with CIE coordinates of (0.51, 0.38).This approach effectively solves the problem of red-to-blue spectrum shift inherent in OLED with a host-guest system.