Discrimination and control of the exciton-recombination region of thermal-stressed blue organic light-emitting diodes

Abstract

Organic light-emitting diodes (OLEDs) suffer from carrier imbalance under high temperature. We improved their thermal stability by using the space interlayers adjacent to charge transport layers. The current efficiency of...

Effect of the Glass Transition Temperature of Organic Materials on Exciton Recombination Region of Deep Blue OLED under Thermal Stress

“…Although the mobility at 80 °C is 0.47 × 10 −4 cm 2 V −1 s, which is decreased compared to those at other temperatures, it is still 6.7 times higher than that of our previously reported device using low T g material of 1,3,5‐tris(1‐phenyl‐1H‐benzo[d]imidazol‐2‐yl)benzene (TPBi, T g = 122 °C) as the functional material. [ 33 ] The results indicated that owing to the stable physical and chemical properties of the materials with better heat resistance, effective carrier transport was guaranteed and the thermal stability of the devices was enhanced. In addition, interfacial morphology was maintained under high temperatures, which further contributed to the enhanced thermal stability.…”

“…While in our previous study, the current densities at different temperatures were 1.06, 1.90, 2.26, and 1.85 mA cm −2 , and the luminous intensities at different temperatures were 99.88, 200.5, 273.3, and 248 cd m −2 , respectively. [ 33 ] This indicated that the thermal stability was significantly enhanced. In Figure 3b, the OLED annealed at 80 °C reaches exciton complex equilibrium faster compared to that annealed at 100 °C, which is reflected in the larger current efficiency (CE) obtained at the low brightness.…”

“…In addition, the turn‐on voltage of the pristine or annealed OLED is stabilized at 2.7 V, which decreases by 0.5 V compared to the OLED using low T g charge transport materials. [ 33 ] Such a phenomenon was attributed to the energy‐level match between layers, as well as the mobility of the transporting material. As illustrated in Figure 2, the mobility of electron is much lower than that of the hole, so the charge recombination could occur at the interface of EML/ETL.…”

“…In addition, the electron injection from Liq to B3PYMPM was much easy due to the deeper LUMO level of B3PYMPM than that of Liq, while there is an energy gap of 0.5 eV for the electron injection for the OLED based on low‐ T g material. [ 33 ] Therefore, the turn‐on voltage was optimized for the OLED based on high‐ T g material. In contrast, the high mobility (10 −5 cm 2 V −1 s) [ 34 ] of ETL B3PYMPM should also play a role in the optimized turn‐on voltage.…”

Realizing high efficiency and luminance in green, yellow and blue organic light emitting diode by deoxyribonucleic acid

“…Meanwhile, this indicates that the emissions of device A1-A4 both originate from the exciton recombination region between TAPC and LiF/Al, this is consistent with the above discussion. In other words, using DNA-CTMA as the EBL, the charge balance enables efficient confinement of the exciton within Alq 3 layer, and the region of exciton recombination is consistently confined to within the Alq 3 layer, although there is a certain displacement of the recombination region [24].…”