Simple and efficient non-doped deep-blue and white organic light-emitting diode based on hybridized local and charge transfer (HLCT) materials

Abstract

Achieving ultra-simple and high-efficiency monochrome and white organic light-emitting diodes (OLEDs) is still a long-running challenge in the fields of display and solid-state lighting sources. In recent years, researchers have focused on hybridized local and charge transfer (HLCT) materials due to theoretically complete exciton utilization, low-efficiency roll-off, and doping-free preparation process and have successfully developed a series of blue HLCT materials with excellent electroluminescence (EL) performance. However, all HLCT emitter-based white OLEDs have not been reported to date. Recently, our group reported two complementary HLCT materials, 9-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (pCzAnN) (blue) and 4-(7-(10-(naphthalen-2-yl)anthracene-9-yl)benzo[c][1,2,5]thiadiazol-4-yl)-N,N-diphenylaniline (TBAN) (yellow), which simultaneously exhibit just opposite carrier transport properties. Herein, by carrier balance strategy, the fabricated pCzAnN-based non-doped deep-blue OLED achieves the maximum external quantum efficiency (EQE) of 9.36%, which is among the highest values reported to date for HLCT-based non-doped blue OLEDs. At the same time, the efficient non-doped yellow OLED with TBAN emitter was demonstrated with maximum luminance and EQE reaching 76 600 cd m⁻² and 6.19%, respectively. On the basis of the above, the first all HLCT emitter-based white OLED was proposed by inserting a carrier regulation layer between non-doped complementary light-emitting layers (pCzAnN and TBAN). The resulting white OLEDs realize the maximum EQE exceeding the theoretical limit of 5% for traditional fluorescent OELDs, and the EL spectra can be easily tuned by simply changing the thickness of the exciton regulation layer to obtain a balanced white light emission with the maximum color rendering index of 84. This work opens up a new way for the development of ultra-simple and high-performance white OLEDs.