Organic semiconductors have attracted considerable interest over the last decade due to an immense improvement in the performance of electronic devices based on these materials. This attention has mainly been focused on conjugated polymers and oligomers, as well as small molecules which can be utilized as active layers in devices such as field-effect transistors (FETs), [1,2] photovoltaic cells, [3] and light-emitting diodes.[4] An interesting group of materials with potential application as organic semiconductors in electronic devices are columnar discotics. [5,6] These mesogens consist of an aromatic core, which can be chemically modified by peripheral substitution (e.g., with alkyl chains), and self-assemble into one-dimensional (1D) columnar superstructures that then arrange in a two-dimensional (2D) lattice. The overlapping of the p orbitals of adjacent molecules within the columns ensures 1D intracolumnar charge-carrier transport. Another essential requirement for undisturbed 1D charge migration along the columns is a high degree of long-range order in the active layer which is deposited between the electrodes. [7] Local defects at domain boundaries in unoriented layers can trap charge carriers and significantly decrease the device performance. Thus, the development of appropriate processing techniques became an essential challenge for the fabrication of unperturbed long-range-oriented organic semiconductors. This close relationship between supramolecular structure and electronic properties has been investigated impressively for planar metallophthalocyanine (Pc) and metalloporphyrin derivatives, in which the charge-carrier mobility of the holes depends strongly on the processing technique.[8±11] For vacuum-deposited thin layers of phthalocyanine, the mobility varied from 10 ±4 cm 2 V ±1 s ±1 for nickel Pc [8] to 0.02 cm 2 V ±1 s ±1 for copper Pc. [9,10] Other processing techniques, such as solution deposition onto substrates with a friction-oriented poly(tetrafluoroethylene) (PTFE) layer [12] and the Langmuir±Blodgett (LB) method, require chemical substitution of Pc, which results in decreased mobility in comparison to samples prepared by vacuum deposition.[13]The history of discotic liquid-crystalline hexa-peri-hexabenzocoronene (HBC) derivatives as semiconductors is significantly shorter than that of phthalocyanines. Nevertheless, HBC derivatives have been successfully exploited in photovoltaic devices and field-effect transistors.[14] FETs were prepared by solution casting on substrates with the pre-oriented PTFE layer, resulting in uniaxial columnar order with an edge-on arrangement of the molecules.[15] The high supramolecular orientation was confirmed by field-effect anisotropy: the charge-carrier mobilities along the columns were significantly higher than in the perpendicular direction. [16] The high anisotropy of the charge-carrier mobility was demonstrated by flash-photolysis time-resolved microwave conductivity measurements.[17] The LB technique [18] and zone crystallization [19] have also been re...
This paper reports the effects of polydispersity in conjugation length on polymer light-emitting diode (PLED) device performance. For this study a di-alkoxy substituted pentamer of p-phenylenevinylene (5PV) was blended with a small amount of a lower band gap poly(p-phenylenevinylene) (PPV) or a small amount of a di-alkoxy substituted p-phenylenevinylene type nonamer (9PV). We also fractionated two different di-alkoxy substituted oxadiazole-PPVs and blended the high molecular weight, lower band gap fraction, into a matrix of the lower molecular weight, higher band gap, polymer. It was found that incorporation of a small amount of the low band gap material significantly degraded PLED device performance. To further test the significance of polydispersity we synthesized a low molecular weight narrow polydispersity PPV. Devices made with this PPV were about 2 orders of magnitude better in LED external quantum efficiency when compared to a high molecular weight, higher polydispersity PPV of identical structure. These findings are significant in that they point to the importance of controlling the polydispersity in conjugation length for obtaining efficient PLEDs. They also indicate the importance of controlling polydispersity when comparing one polymer structure to another.
A scalable manufacturing process for fabricating active-matrix backplanes on low-cost flexible substrates, a key enabler for electronic-paper displays, is presented. This process is based on solution processing, ink-jet printing, and laser patterning. A multilayer architecture is employed to enable high aperture ratio and array performance. These backplanes were combined with E Ink electrophoretic media to create high-performance displays that have high contrast, are bistable, and can be flexed repeatedly to a radius of curvature of 5 mm
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.