Search

In this article, four "A(3)+B(2)+C(2)"-type hyperbranched conjugated polymers (P1-P4) containing hexaphenylbenzene as the core were synthesized successfully for the first time with high yields through one-pot Suzuki polymerization reaction. The copolymerization percent of 1,3,4-oxadiazole units was adjusted to investigate the effect of polymer composition on the physical, optical, and EL properties. All polymers were well-characterized and exhibited good solubility, film-forming ability, and thermal stability. Both the solution and the films of these hyperbranched polymers emitted pure and stable deep-blue light emission, and their PL spectra did not change after annealing at 150 degrees C for 0.5 h in air, indicating that the hyperbranched structure, coupled to the introduced hexaphenylbenzene moieties, effectively suppressed the formation of aggregation excimer and keto defects. Two-layer PLED devices were fabricated to investigate the electroluminescence properties of these hyperbranched polymers, and P3 demonstrated a maximum luminance efficiency of 0.72 cd/A and a maximum brightness of 549 cd/m(2) at 16.5 V.

A polythiophene derivative with the simplest conjugated side chain, poly(3-hexy-1-enylthiophene) (P3HET), was synthesized by Stille self-coupling reaction. A comparative study of the newly synthesized polymer with poly(3-hexylthiophene) (P3HT), one of the most widely investigated optoelectronic materials, is presented. The effect of double bond (C=C) on the side chain toward thermal stability and optical and electronic properties was fully characterized by TGA, UV-vis absorption spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. The hole mobility of P3HET determined by the space-charge-limited current (SCLC) model is 6.7 x 10(-3) cm(2)/V s, which is comparable to P3HT with similar molecular weight and regularity and 1 order of magnitude higher than most conjugated-side-chain polythiophene derivatives. Polymer solar cells (PSCs) and field effect transistors (FETs) were fabricated respectively to exploit its potential applications in optoelectronic devices.

In the past decade, tremendous progress has been made in organic field-effect transistors (OFETs). Their real applications require further development of device performance. OFETs consist of organic semiconductors, dielectric layers, and electrodes. Organic semiconductors play a key role in determining the device characteristics. The properties of the organic semiconductors, such as molecular structure and packing, as well as molecular energy levels, can be properly controlled by molecular design. Therefore, we designed and synthesized a series of organic molecules. The synthesized organic semiconductors exhibit excellent field-effect properties due to strong intermolecular interactions and proper molecular energy levels. Meanwhile, the influence of the device fabrication process, organic semiconductor/dielectric layer interface, and organic layer/electrode contact on the device performance was investigated. A deep understanding of these factors is helpful to improve field-effect properties. Furthermore, single-crystal field-effect transistors are highlighted because the single-crystal-based FETs can provide an accurate conducting mechanism of organic semiconductors and higher device performance as compared with thin film FETs.

Four donor-acceptor functionalized molecular materials with symmetrical structures have been synthesized and investigated for their use in optoelectronic applications. These pi-conjugated molecules consist of one electron-donating moiety, for instance, carbazole, triphenylamine, or phenothiazine at the center, and two acceptors at each side. Introduction of different donor moieties decreases the band gaps allowing a fine-tuning of the optical and electrical properties. These materials exhibit multifunctional properties, such as a red light-emitting behavior and a large photovoltaic effect. Red organic light-emitting diodes were fabricated in a facile nondoping configuration based on these materials. Saturated red-emission is observed with a CIE of x = 0.64 and y = 0.33, and an external quantum efficiency of 0.19%. In addition, our first observation of photovoltaic response in the pi-conjugated molecule with donor-acceptor-donor structure is reported. The organic single-component photovoltaic cells were fabricated and characterized. Their open-circuit voltage and short-circuit current density are 1.1 V and 0.07 mA cm(-2), respectively. The photovoltaic effect corresponds to the absorption characteristics of the compound and depends on the nature of the electron-donating group.