Zhenyu Tang

Low-energy consumption and high-color-quality white organic light-emitting diodes

White organic light-emitting diodes (WOLEDs) offer a range of attractive characteristics include easily processable, glare-free and generate light over a large area. However, high-energy consumption, unreliable and low-color-quality are key issues limiting the future of WOLEDs. Enormous efforts in chemistry and the materials sciences to design better materials as well as in physics and engineering to invent new device concepts and design suitable fabrication schemes have been endeavored. This article reviews current developments in the field of WOLEDs and puts a special focus on new device concepts and on approaches to low-energy consumption and high-color-quality WOLED manufacturing.

Enhanced photovoltaic performance of inverted polymer solar cells through atomic layer deposited Al2O3 passivation of ZnO-nanoparticle buffer layer

In this work, an atomic layer deposited (ALD) Al2O3 ultrathin layer was introduced to passivate the ZnO-nanoparticle (NP) buffer layer of inverted polymer solar cells (PSCs) based on P3HT:PCBM. The surface morphology of the ZnO-NP/Al2O3 interface was systematically analyzed by using a variety of tools, in particular transmission electron microscopy (TEM), evidencing a conformal ALD-Al2O3 deposition. The thickness of the Al2O3 layers was optimized at the nanoscale to boost electron transport of the ZnO-NP layer, which can be attributed to the suppression of oxygen vacancy defects in ZnO-NPs confirmed by photoluminescence measurement. The optimal inverted PSCs passivated by ALD-Al2O3 exhibited an ∼22% higher power conversion efficiency than the control devices with a pristine ZnO-NP buffer layer. The employment of the ALD-Al2O3 passivation layer with precisely controlled thickness provides a promising approach to develop high efficiency PSCs with novel polymer materials.

Extremely low-efficiency roll-off of phosphorescent organic light-emitting diodes at high brightness based on acridine heterocyclic derivatives

Three novel host materials, IpCm-PhBzAc (1,3-(4-(12,12-dimethylbenzofuro[3,2-b]acridin-7(12H)-yl)phenyl)-6-isopropyl-4H-chromen-4-one), DpAn-BzAc (2,10-(4-(12,12-dimethylbenzofuro[3,2-b]acridin-7(12H)-yl)phenyl)-10-phenylanthracen-9(10H)-one) and DpTrz-BphBzAc (3,7-(4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)-12,12-dimethyl-7,12-dihydrobenzofuro[3,2-b]acridine) have been designed and synthesized, and their utilization as host materials for phosphorescent organic light-emitting diodes (PhOLEDs) has been investigated. We have fabricated PhOLEDs using green bis(2-phenylpyridine)iridium(III) acetylacetonate as doped emitters and two hosting schemes, which are the single host system consisting of BzAc derivatives and the co-host system with 1,3-bis(carbazolyl)benzene. We found that the PhOLEDs with the co-host system of DpAn-BzAc and DpTrz-BphBzAc achieved CEs of 57.1 cd A−1 and 53.0 cd A−1, with corresponding efficiency roll-off of only 7.6% and 0.9%, respectively, from the maximum to the practical brightness of 5000 cd m−2. Extremely reduced efficiency roll-off values for BzAc-based PhOLEDs were attributed to their superior thermal stability and excellent bipolar transport properties, and a small singlet–triplet energy gap also afforded efficient reverse intersystem crossing, thus reducing the triplet density of the host for PhOLEDs.

Study on organic/inorganic hybrid light emitting diode

The technique of organic light-emitting diodes developed rapidly over the last decade and small size OLED panels has also been commercially applied. However, organic semiconductors exhibit relatively poor electrical and thermal behavior and the device stability is always a tough issue since the high sensitivity to the environment, such as the water, oxygen, temperature, and so on. Therefore, the organic-inorganic hybrid light-emitting devices become research focus for combining both the high electron mobility of inorganic semiconductors and the extraordinary optoelectronic properties of polymers. However, according to previous research results, there are still problems such as low brightness, poor color rendering, low efficiency and low current density etc. Here, we present a novel inverted organic-inorganic hybrid blue fluorescent device with the hybrid p-n junction structure using n-type GaN (n-GaN) and organic semiconductor layers, which was proved to have extremely high luminance and low driving voltage. Single layer n-GaN with thickness of 2.5 um on patterned sapphire substrate (PSS) was used in this paper because it has excellent electrical conductivity and outstanding thermal conductivity. Based on this organic-inorganic hybrid system, we have proved a high-brightness and low turn-on voltage light-emitting devices.

Ultrahigh-luminance organic light-emitting diodes using LiF/MgAg as cathode for the application of both surface emission

ABSTRACT The effect of different species of cathode on the performance of organic light-emitting diodes under direct current drive has been investigated in this paper. The organic light-emitting diode using LiF/Al and LiF/MgAg layer as cathode has been fabricated, and the luminance of device with cathode structure of LiF/MgAg was found to realize higher efficiency. The performance of the device was found to be improved greatly due to efficient electron injection from MgAg cathode. Moreover, a configuration of LiF/MgAg/IZO (indium zinc oxide) was developed, finding that both the top-emitting intensity and the bottom-emitting intensity achieve very-high luminance, and in this basis, transparent OLEDs with the extremely high-luminance of about 100,000 cd/m2 has been realized, which is considered as the highest luminance among the previous works.