IntroductionOver the past decade, several conjugated organic oligomers and polymers have been developed for potential use in low-cost semiconductor applications to replace their higher-cost inorganic counterparts. The most attractive aspect of these organic materials is that their structures can be diversifi ed and their physical or chemical properties tuned through strategic molecular design. [1][2][3][4][5][6][7][8][9] Among the variety of organic semiconductors developed, thiophene-based materials have emerged as an important class because of their high chemical and electrochemical stability, the accessibility of their preparation for thiophene synthesis, and the availability of welldeveloped/regioselective ring-ring coupling methodologies. [ 10 , 11 ] Furthermore, the properties of oligo/polythiophene cores can be effi ciently tuned by introducing appropriate substitutions. To date, the fi eld-effect transistor (FET) mobilities in devices composed of oligomeric thiophene semiconductors are generally higher than those obtained from conjugated polymers. Oligomeric thiophene semiconductor polymers engage in longrange packing, and effi cient charge transport is directly related to the long-range packing of molecules in semiconductor fi lms. Many synthetic methods have been developed to functionalize the α -and ω -ends of conjugated thiophene ring systems to increase the solubility and stability toward oxidation or to infl uence the solid-state ordering of oligothiophenes without affecting the planarity of the conjugated backbone. [ 12 , 13 ] The present study was devised based on the following three considerations: i) previously reported organic semiconductors have generally shown J-aggregation [ 14 ] with head-to-tail molecular stacking; [ 15 ] ii) large area π -stacking between adjacent molecules can be realized by H-aggregation, which occurs when molecules stack side by side; [ 16 ] and iii) H-aggregation induces stable morphologies in thin fi lms and reproducible transistor performances. We describe a novel synthetic strategy to induce H-aggregation between adjacent molecules in the thin fi lm state. We designed four types of quaterthiophene derivative with end-groups composed of cyclohexyl ethyl (CE4T), cyclohexyl butyl (CB4T), dicyclohexyl ethyl (DCE4T), and dicyclohexyl butyl (DCB4T). UV-vis absorption and grazing-incidence wideangle X-ray scattering (GIWAXS) analyses indicated that the asymmetric derivatives, CE4T and CB4T, tended to undergo H-Aggregation Strategy in the Design of Molecular Semiconductors for Highly Reliable Organic Thin Film TransistorsFour new quaterthiophene derivatives with end-groups composed of dicyclohexyl ethyl (DCE4T), dicyclohexyl butyl (DCB4T), cyclohexyl ethyl (CE4T), and cyclohexyl butyl (CB4T) were designed. All materials showed high solubility in common organic solvents. UV-vis absorption measurements showed that the quaterthiophene derivatives with asymmetrically substituted cyclohexyl end-groups (CE4T and CB4T) preferred H-type aggregation whereas those with symmetrica...
The integration of electrochromic (EC) and thermochromic (TC) systems is important for realizingmultifunctional smart windows, which can adaptively control light transmittance and solar energy in response to diverse external stimuli. In this study, we developed an all-solid-state multifunctional smart window, in which tungsten oxide (WO3)-based EC and vanadium oxide (VO2)-based TC cells were integrated into a single device. In hybrid smart windows, the WO3-based EC layer modulates optical transmission in response to electrical voltage, while the VO2-based TC layer regulates solar energy transmission responding to the surrounding temperature. Therefore, such windows can control optical transmission and solar energy transmission in response to an electric stimulus and temperature change simultaneously or independently, allowing for a selective modulation of light in the visible and near-infrared regions. We demonstrated the viability of the proposed integrated smart window system by varying its optical transmission in four different optical states depending on its EC reaction and TC behavior. The concept for the integration of EC and TC cells into a single device can pave the way for next-generation multifunctional smart window systems.
Graphene synthesized via chemical vapor deposition is a notable candidate for flexible large-area transparent electrodes due to its great physical properties and its 2D activated surface area. Electrochromic devices in optical displays, smart windows, etc are suitable applications for graphene when used as a transparent conductive electrode. In this study, various-layer graphene was synthesized via chemical vapor deposition, and inorganic WO(x) was deposited on the layers, which have advantageous columnar structures and W(6+) and W(4+) oxidation states. The characteristics of graphene and WO(x) were verified using optical transmittance, Raman spectroscopy, x-ray photoelectron spectroscopy and scanning electron microscopy. The optimum transparent conductive electrode condition for controlling graphene layers was investigated based on the optical density and cyclic voltammetry. Electrochromic devices were fabricated using a three-layer graphene electrode, which had the best optical density. The graphene in the flexible electrochromic device demonstrated a potential for replacing ITO in flexible electronics.
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