Chuanhui Cheng

Preparation of Copper Phthalocyanine Crystals Using Solvothermal Synthesis

Abstract A novel solvothermal synthesis method for the direct growth of β-form crystals of copper phthalocyanine(CuPc) is presented in this article. With quinoline as solvent, crystals were grown after cooling the reaction mixture of 1,3-diiminoisoindoline and copper oxide, heated for 9 h at 270°C, to room temperature in an autoclave. These high quality crystals were suitable for characterization measurements. The single-crystal diffraction data show a monoclinic system unit cell: a =1.4668(3) nm, b =0.48109(10) nm, c =1.9515(7) nm, α=90°, β=121.04(2)°, γ=90°, where the corresponding cell volume is 1.17991 nm 3 . Needle-like single crystals of CuPc up to 10.5 mm in length were obtained. The influences of different temperatures, reaction time and solvent volume on the crystal yields were also discussed. Optimum reaction conditions were 10 mL of quinoline, at 270°C for 8 h.

Low threshold two-dimensional organic photonic crystal distributed feedback laser with hexagonal symmetry based on SiN

We report on the characterization of low threshold second-order organic photonic crystal distributed feedback laser based on SiN with hexagonal lattice. SiN can increase the index contrast in the photonic crystal distributed feedback as well as the confinement in the waveguide which results in a decrease in the threshold. Low threshold energy of 0.65kW∕cm2 and full width at half maximum of 0.9nm were achieved in lasers. As a result, we observe surface-emitting lasing action and hexagonal emission pattern of side beams whose direction slightly deviates from the normal. We explain the feedback mechanisms by using semiclassical laser theory.

Photoemission spectroscopy study of oxygen spectrum and the chemical failure process of Alq3-based light-emitting devices

Tris (8-hydroxyquinolino) aluminum (Alq3) films and their chemical failure process are investigated using x-ray photoelectron spectroscopy. We make sure that the O 1s spectrum of the pristine Alq3 only has one component which is in contrast to the current controversy on this issue. Our experiments further indicate that the chemical failure process of Alq3 holds the critical role to understand this problem. The chemical failure process also shows the organic carbon contamination and the replacement reaction between Alq3 and water, ultimately resulted in the failure of the device. These fundamental results provide a basis understanding for future development of Alq3-based light emitting devices.

Emission Characteristics and Performance Comparison of Organic Lasers with One-Dimensional Distributed Feedback

This paper presents optically pumped solid-state organic lasers based on tris(8-hydroxyquinoline) aluminum (Alq3) doped with the laser dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidy 1-9-enyl)-4H-pyran (DCJTB, 2 wt %) using resonator which offers one dimensional distributed feedback. The lasers have been fabricated by deposition of organic films on top of suitable grating microstructures etched into SiN layer. The devices operating in the red spectral region are highly efficient and exhibit low threshold for oscillation (0.3 kW/cm2). The operating characteristics of the lasers are investigated in detail. The laser oscillation is obtained by optimizing the organic film thickness. The ratio of slot width to grating period is another important parameter to decrease the lasing threshold.

Significant performance enhancement of inverted organic light-emitting diodes by using ZnIx as a hole-blocking layer

A highly efficient inverted organic light emitting diode using 1.0 nm-thick ZnIx as a hole-blocking layer is developed. We fabricate devices with the configuration ITO/ZnIx (1.0 nm)/Alq3 (50 nm)/NPB (50 nm)/MoO3 (6.0 nm)/Al (100 nm). The deposition of a ZnIx layer increases the maximum luminance by two orders of magnitude from 13.4 to 3566.1 cd/m2. In addition, the maximum current efficiency and power efficiency are increased by three orders of magnitude, and the turn-on voltage to reach 1 cd/m2 decreases from 13 to 8 V. The results suggest that the electron injection efficiency is not improved by introducing a ZnIx layer. Instead, the improved device performance originates from the strong hole-blocking ability of ZnIx. This work indicates that layered materials may lead to novel applications in optoelectronic devices.

The inorganic-organic hybrid junction with n-ZnO nanorods/p-polyfluorene structure grown with low-temperature aqueous chemical growth method

The inorganic-organic hybrid junction was synthesized on ITO glass substrate, which was consisted of an n-type ZnO nanorods (NRs) grown by low-temperature aqueous chemical growth method and a p-type polyfluorene (PF) organic film fabricated by spin-coating. The experimental results indicate that densely and uniformly distributed ZnO nanorods are successfully grown on the PF layer. The thickness of the PF layer plays a dominant role for the current-voltage (I–V) characteristic of the ZnO NRs/PF inorganic-organic hybrid junction device, and a p-n junction with obviously rectifying behavior is achieved with optimal PF layer thickness. The photoluminescence (PL) spectrum covering the broad visible range was obtained from the n-ZnO nanorods/p-polyfluorene (PF) structure, which was originated from the combination of the PF-related blue emission and the ZnO-related deep level emission.