Over the last 20 years, tremendous progress has been achieved in the design and fabrication of organic electronic devices. High performance LEDs, transistors, and memory devices—the materials science journals have it all! Follow the continuing progress and the latest breakthroughs in the field of organic electronics in our top-quality journals.
High-Performance Organic Field-Effect Transistors
Adv. Mater., DOI: 10.1002/adma.200802733
A capillary pen drawing technique, developed as a new patterning methodology for the large-area patterning and fabrication of organic electronics, provides several advantages over conventional approaches: the method is simple and versatile, there are no restrictions on the patterning shapes that could be produced, and the method can be tailored to a variety of substrates.
Film-like conjugated microporous polymers (CMPs) are fabricated by the novel strategy of carbazole-based electropolymerization. The CMP film storing a mass of counterions acting as an anode interlayer provides a significant power-conversion efficiency of 7.56% in polymer solar cells and 20.7 cd A−1 in polymer light-emitting diodes, demonstrating its universality and potential as an electrode interlayer in organic electronics.
Low-operating-voltage flexible organic thin-film transistors with high thermal stability using DPh-DNTT and SAM gate dielectrics are reported. The mobility of the transistors are decreased by 23% after heating to 250 °C for 30 min. Furthermore, flexible organic pseudo-CMOS inverter circuits, which are functional after heating to 200 °C.
The preparation of brominated tetraazaperopyrenes, their crystal structures, and their electrochemical properties are reported. These N-heterocyclic peropyrene derivatives are well-suited materials for the preparation of n-channel conducting organic thin-film transistors either by vacuum deposition or by solution processing. Additionally, the fabrication of a complementary ring oscillator on a flexible substrate is described.
A high molecular weight conjugated polymer based on alternating electron-rich and electron deficient fused ring systems provides efficient polymer solar cells when blended with C60 and C70 fullerene derivatives. The morphology of the new polymer/fullerene blend reduces bimolecular recombination and allows reaching high fill factors and power conversion efficiencies for films up to 300 nm thickness.
A strategy towards efficient mechanochromic luminogens with high contrast is developed. The twisted propeller-like conformations and effective intermolecular interactions not only endow the luminogens with AIE characteristics and high efficiency in the crystalline state, but also render them to undergo conformational planarization and disruption in intermolecular interactions upon mechanical stimuli, resulting in remarkable changes in emission wavelength and efficiency.
Bifunctional star-burst amorphous molecular materials displaying both efficient solid-state luminescence and high hole-transport properties are developed in this study. A high external electroluminescence quantum efficiency up to 5.9% is attained in OLEDs employing the developed amorphous materials. It is revealed that the spontaneous horizontal orientation of these light-emitting molecules in their molecular-condensed states leads to a remarkable enhancement of the electroluminescence efficiencies and carrier-transport properties.
The optical and electrical properties of the organic semiconductor F8TBT are tailored by changing the position of the alkyl side chains. A conventional form of F8TBT (F8TBT-out) and a form with varied alkyl side-chain position, F8TBT-in, are directly compared in terms of optical properties and light-emitting-diode device performance. This illustrates how the placement of side chains has a very important role for device optimization.
A high organic field-effect transistor mobility (0.29 cm2V−1s−1) and bulk-heterojunction polymer solar cell performance (PCE of 6.82%) have been achieved in a low bandgap alternating copolymer consisting of axisymmetrical structural units, 5,6-difluorobenzo-2,1,3-thiadiazole. Introducing the fluorine substituents enhanced intermolecular interaction and improved the solid-state order, which consequently resulted in the highest device performances among the 2,1,3-thiadiazole-quarterthiophene based alternating copolymers.
Organic-inorganic composites fabricated via co-evaporation of two materials reveal a filamentous nanostructure with filaments preferentially oriented perpendicular to the substrate plane. This growth process can be controlled by changing the substrate temperature so that for films evaporated on cooled substrates no filament growth can be detected.
The effects of confinement on the morphology and charge transport properties of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) are studied using quantitative X-ray diffraction and field-effect transistor measurements. Polymer crystallinity is found to limit charge transport in the thinnest films while crystalline texture and intergrain connectivity modulate carrier mobility in thicker films.
A simple and versatile fabrication process is used to define conducting polymer microelectrode arrays (MEAs), patterning at the same time the recording electrodes as well as the insulating layer. Thanks to the low impedance of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) electrodes, these MEAs allow in vitro recording of action potentials from rat hippocampus slices.
Silver nanowires (Ag NWs) are introduced as a viable alternative to thermally evaporated silver metal top electrodes. Solution-processable Ag NWs are spray-deposited as highly conductive and transparent electrode layers in semitransparent poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solar cell devices. Their optical properties in semitransparent organic photovoltaic devices are presented and they show comparable performance to reference devices.
This Review discusses recent progress in electrolyte-gated transistors (EGTs). EGTs employ a high-capacitance electrolyte as the gate insulator layer, which affords low voltage operation and high drive currents. The Review covers EGT operation mechanisms, the development of new solid electrolyte materials for use in EGTs and emerging applications of these devices in printed digital circuits, flexible displays, biosensors, and fundamental transport measurements.
The power conversion efficiency of donor-acceptor organic solar cells now reaches over 10% in single-junction and tandem cells. Empirical models suggest that the maximum efficiency may be limited at 10–12%, yet recent, more refined detailed-balance models indicate that, under favorable conditions, efficiencies in the range of 20–24% can be achieved.
In this Progress Report, the most recent literature on diketopyrrolopyrrole-containing polymers developed for field-effect transistor applications is reviewed and the structure–property relations of importance for achieving high performance n- and p-type transistor materials are discussed in detail.
A series of thiophene derivatives is analyzed with regard to their luminescent properties. Calculations at the TDDFT level and a semiclassical approach for vibrational broadening are applied to predict the emission spectra. The use of the M06-2X functional and inclusion of solvent effects with the state-specific formulation of the polarizable continuum model solvent model gives results that are in good agreement with the experimental data.
Copolymers with a triscarbazole hole-transport group and an oxetane or benzocyclobutene crosslinkable group can be readily thermally crosslinked on timescales of 30 min or less, with rapid thermal processing (RTP) being highly effective for this purpose. Devices with RTP-crosslinked hole-transport layers and spin-coated emissive layers exhibit high external quantum efficiencies of up to 15%.
Extensive intramolecular π-conjugation is considered to be requisite in the design of organic semiconductors. Here, two inkjet pigments, epindolidione and quinacridone, that break this design rule are explored. These molecules afford intermolecular π-stacking reinforced by hydrogen-bonding bridges. Air-stable organic field effect transistors are reported that support mobilities up to 1.5 cm2/Vs with T80 lifetimes comparable with the most stable reported organic semiconducting materials.
Structure-property correlations currently lacking in organic photovoltaics are examined. To gain a better understanding of such relationships and ultimately attain higher efficiencies, researchers should look toward employing LUMO-reducing moieties and effectively using electron-withdrawing and side-chain substitutents to effectively tune polymer–PCBM interactions.
Thiazole is an electron-accepting heterocycle due to electron-withdrawing nitrogen of imine, several thiazole related moieties have been widely introduced into organic semiconductors and yielded high performance in organic electronic devices. This article reviews recent developments in thiazole, bithiazole, thiazolothiazole and benzobisthiazole-based small molecule and polymer semiconductors for applications in organic field-effect transistors, solar cells and light-emitting diodes.
A comprehensive overview on the subject of current injection in organic thin-film transistors is given: physical principles concerning energy level (mis)alignment at interfaces, models describing charge injection, technologies for interface tuning, and techniques for characterizing devices. Finally, a survey of the most recent accomplishments in the field is given.