We present a critical review of semiconducting/light emitting, liquid crystalline materials and their use in electronic and photonic devices such as transistors, photovoltaics, OLEDs and lasers. We report that annealing from the mesophase improves the order and packing of organic semiconductors to produce state-of-the-art transistors. We discuss theoretical models which predict how charge transport and light emission is affected by the liquid crystalline phase. Organic photovoltaics and OLEDs require optimization of both charge transport and optical properties and we identify the various trade-offs involved for ordered materials. We report the crosslinking of reactive mesogens to give pixellated full-colour OLEDs and distributed bi-layer photovoltaics. We show how the molecular organization inherent to the mesophase can control the polarization of light-emitting devices and the gain in organic, thin-film lasers and can also provide distributed feedback in chiral nematic mirrorless lasers. We update progress on the surface alignment of liquid crystalline semiconductors to obtain monodomain devices without defects or devices with spatially varying properties. Finally the significance of all of these developments is assessed.

Ordered materials for organic electronics and photonics.

Organic semiconducting materials offer the advantage of solution processability into flexible films. In most cases, their drawback is based on their low charge carrier mobility, which is directly related to the packing of the molecules both on local (amorphous versus crystalline) and on macroscopic (grain boundaries) length scales. Liquid crystalline ordering offers the possibility of circumventing this problem. An advanced concept comprises: i) the application of materials with different liquid crystalline phases, ii) the orientation of a low viscosity high temperature phase, and, iii) the transfer of the macroscopic orientation during cooling to a highly ordered (at best, crystalline-like) phase at room temperature. At the same time, the desired orientation for the application (OLED or field-effect transistor) can be obtained. This review presents the use of molecules with discotic, calamitic and sanidic phases and discusses the sensitivity of the phases with regard to defects depending on the dimensionality of the ordered structure (columns: 1D, smectic layers and sanidic phases: 2D). It presents ways to systematically improve charge carrier mobility by proper variation of the electronic and steric (packing) structure of the constituting molecules and to reach charge carrier mobilities that are close to and comparable to amorphous silicon, with values of 0.1 to 0. 7 cm 2 . V -1 . s -1 . In this context, the significance of crosslinking to stabilize the orientation and liquid crystalline behavior of inorganic/organic hybrids is also discussed.

Liquid crystalline ordering and charge transport in semiconducting materials.

Mesogens with a general structure bis(alkylthiophene)arene, in which the central arene moiety is 1,4-benzene, 2,5-pyridine, 3,6-pyrimidine, 2,6-naphthalene and 2,6-dithieno[3,2-b;2′,3′-d]thiophene, were synthesized, and the effect of the central unit and the length of the alkyl chains on the liquid crystalline behavior was studied by differential scanning calorimetry and polarized optical microscopy, and in the case of 1,4-bis(5-tridecylthiophen-2-yl)benzene (2a) and 2,6-bis(5-tridecylthiophen-2-yl)DTT by synchrotron X-ray analysis. Several 2,5-bis(5-alkylthiophen-2-yl)pyridines and 1,4-bis(5-tridecylthiophen-2-yl)benzene 2a exhibit a rare transition – formation of the SmF phase directly from the isotropic liquid; in the case of 2a, formation of higher ordered smectic phases was observed on further cooling. Hole-transporting properties of 2a in different mesophases were studied by the time-of-flight technique. The hole mobility, μh, in SmF reached 6 × 10−3 cm2 V−1 s−1 and increased with an increase of the order of the mesophase up to 0.02 cm2 V−1 s−1 in the S1 phase (tentatively assigned as the crystal G phase), ∼0.09 cm2 V−1 s−1 in the S2 phase (tentatively assigned as the crystal H phase), and 0.11 cm2 V−1 s−1 in the crystalline phase at 70 °C.

Bis(5-alkylthiophen-2-yl)arene liquid crystals as molecular semiconductors

Liquid crystals are often regard as a fourth state phase of matter alongside solids, liquids and gases. It has been estimated that one out of every ten new synthetic compounds is a liquid crystal, mainly due to the fact that liquid crystals have been used in Liquid Crystalline Displays (LCDs) for over 50 years. Liquid crystals, often referred to as mesogens, exhibit an unique range of ordered mesophases with anisotropic physical properties, such as optical, magnetic and dielectric anisotropy, for example. These highly anisotropic properties and the ability of liquid crystals to self-organize on surfaces, has led to them being, are used in a wide range of non-LCD applications. These applications include photochromics, pressure sensitive paints, optical retarders and optical compensation films, etc. Highly crosslinked, anisotropic polymer networks, derived from photopolymerisable liquid crystals, so-called reactive mesogens (RMs), have enabled solution-fabricated organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs) for plastic electronics. This review will be focus on the relatively recent application of liquid crystals, i.e., the 3D/4D printing of reactive mesogens and subsequent polymerization to form anisotropic polymer networks in advanced additive manufacturing applications. It will highlight the challenges of the synthesis and use of new liquid crystalline materials in 3D/4D printing for additive manufacturing applications. It will show how the study of the successful development of design strategies for the synthesis of novel liquid crystals for flat panel displays is inspiring the development of novel photopolymerisable liquid crystals for additive manufacturing. It is intended that this review will serve to inspire chemists, with little or no knowledge of liquid crystals, or liquid crystal chemists, to design and synthesize new liquid crystals for 3D/4D printing. 

Photopolymerisable liquid crystals for additive manufacturing

A class of [5,5′]-diphenyl-[5,5′]-dithiophene (PTTP)-modified methacrylates has been synthesized and free radically polymerized to form graft polymethacrylates with the conducting PTTP segments as pendant side chains. Both the terminal alkyl side chain and spacer between the PTTP segments and polymer backbone could be varied to study fundamental structure–property relationships for this class of materials. Specifically, a group of three different PTTP graft polymethacrylates has been successfully synthesized with the alkyl side chain varying from hexyl to dodecyl. For the dodecyl-terminated poly(4-(5′-(4-dodecylphenyl)-[2,2′-bithiophen]-5-yl)phenethyl methacrylate), p(DPTTPEM), a counterpart, poly(4-(5′-(4-dodecylphenyl)-[2,2′-bithiophen]-5-yl)phenbutyl methacrylate), p(DPTTPBM), where the ethyl spacer was replaced by a butyl group, was synthesized. The experimental results indicated that both the alkyl side chain and spacer significantly affected the reactivity of the PTTP-modified methacrylates during free radical polymerization as well as the physical properties of the resultant graft polymers including solubility, morphology, and electrochemical and electrical properties. Typical field-effect mobilities on the order of 10−5 cm2 V−1 s−1 were observed for all the PTTP monomers in air, which was attributed to their crystalline phase as revealed by differential scanning calorimetry and X-ray diffraction studies. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

https://acswebcontent.acs.org/prfar/2011/media/NUGGET/11473/11473.pdf

Synthesis and characterization of graft polymethacrylates containing conducting diphenyldithiophene for organic thin‐film transistors

Fabrication of display products by low cost printing technologies such as ink jet, gravure offset lithography and flexography requires solution processable semiconductors for the backplane electronics. The products will typically be of lower performance than polysilicon transistors, but comparable to amorphous silicon. A range of prototypes are under development, including rollable electrophoretic displays, active matrix liquid crystal displays (AMLCD's), and flexible organic light-emitting diode (OLED) displays. Organic semiconductors that offer both electrical performance and stability with respect to storage and operation under ambient conditions are required. This work describes the initial evaluation of reactive mesogen semiconductors, which can polymerise within mesophase temperatures, "freezing in" the order in crosslinked domains. These crosslinked domains offer mechanical stability and are inert to solvent exposure in further processing steps. Reactive mesogens containing conjugated aromatic cores, designed to facilitate charge transport and provide good oxidative stability, were prepared and their liquid crystalline properties evaluated. Both time-of-flight and field effect transistor devices were prepared and their electrical characterisation reported.

http://iopscience.iop.org/article/10.1143/JJAP.47.488/pdf

Electrical Properties of Reactive Liquid Crystal Semiconductors

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Michael Heckmeier

Author Tools

Chat about Author

Papers

Electrical Properties of Reactive Liquid Crystal Semiconductors