Organic Semiconductor Single Crystals: A New Platform for Polarization‐Sensitive Photodetection

Channel-restricted meniscus self-assembly for uniformly aligned growth of single-crystal arrays of organic semiconductors

The use of organic materials as radiation detectors has grown, due to the easy processability in liquid phase at room temperature and the possibility to cover large areas by means of low cost deposition techniques. Direct charged-particle detectors based on solution-grown Organic Semiconducting Single Crystals (OSSCs) are shown to be capable to detect charged particles in pulse mode, with very good peak discrimination. The direct charged-particle detection in OSSCs has been assessed both in the planar and in the vertical axes, and a digital pulse processing algorithm has been used to perform pulse height spectroscopy and to study the charge collection efficiency as a function of the applied bias voltage. Taking advantage of the charge spectroscopy and the good peak discrimination of pulse height spectra, an Hecht-like behavior of OSSCs radiation detectors is demonstrated. It has been possible to estimate the mobility-lifetime value in organic materials, a fundamental parameter for the characterization of radiation detectors, whose results are equal to μτcoplanar = (5 .5 ± 0.6 ) × 10−6 cm2/V and μτsandwich = (1 .9 ± 0.2 ) × 10−6 cm2/V, values comparable to those of polycrystalline inorganic detectors. Moreover, alpha particles Time-of-Flight experiments have been carried out to estimate the drift mobility value. The results reported here indicate how charged-particle detectors based on OSSCs possess a great potential as low-cost, large area, solid-state direct detectors operating at room temperature. More interestingly, the good detection efficiency and peak discrimination observed for charged-particle detection in organic materials (hydrogen-rich molecules) are encouraging for their further exploitation in the detection of thermal and high-energy neutrons.

Abstract2D organic semiconductor single crystals comprising one or a few molecular layers of macroscopic lateral sizes are ideal materials for ultrathin, flexible, and transparent field‐effect devices—a platform for transistors and sensors. In recent years, these 2D materials have demonstrated high performance not inferior to their 3D counterparts. However, light emissive properties of 2D organic semiconductor single crystals have not yet been reported, and a combination of high charge‐carrier mobility and bright luminescence in one material is still a challenge for 2D organic optoelectronics. Emissive high‐mobility 2D organic semiconductor based on a [1]benzothieno[3,2‐b]benzothiophene (BTBT)‐derivative, 2,7‐bis(4‐decylphenyl)[1]benzothieno[3,2‐b][1]benzothiophene (DPBTBT), is presented here. DPBTBT molecules self‐organize in large‐area ultrathin single‐crystalline films consisting of one or a few molecular layers. These 2D single crystals perfectly suit as an active layer of organic field‐effect transistors in full accordance with Shockley's model and uniquely combine the high charge‐carrier mobility reaching 7.5 cm2 V–1 s–1 with prominent light emissive properties, which allow a demonstration of the first 2D organic light‐emitting transistor. The high charge‐carrier mobility and thermal stability of the crystalline phases, pronounced luminescence, and good shelf‐life stability suggest that emissive BTBT‐type molecules are a promising avenue for 2D organic optoelectronics.

Previous studies have demonstrated the use of crystalline organic semiconductors to detect and localize the passage of charged particles and energetic radiation. [1-6] In this context, polycrystalline bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) was printed onto polyethylene naphthalate (PEN) substrates patterned with parylene-C dielectric, PEDOT electrodes and gold pads to form fully organic flexible x-ray detectors. The electrodes were patterned using orthogonal photolithography and oxygen reactive ion etching to define a width/length (W/L) = 100 µm/10 µm. An organic voltage divider built using these materials was hot bar bonded to a printed circuit board (PCB) via a flexible conducting tape to form a complete sensor system. The devices were irradiated with a variety of localized and large area sources and the output was extracted from the node between the two resistors and then connected to an operational amplifier via a second PCB. Dark currents for each resistor were in the 100 pA - 1 nA range. The device demonstrated has the potential to be applied in microdosimetry to allow for detection using a cross-section that matches organic tissue forming a solid state tissue equivalent detector (SSTED) [7].

All-Solution-Processed 5 V FeFETs with Organic Semiconductor Single Crystals

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N, cm-3 ) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk-doped organic single crystals. Here, the Hall effect in bulk-doped single-crystal organic semiconductors is measured. A key feature of this work is the ultraslow co-deposition technique, which reaches as low as 10-9 nm s-1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N, cm-3 ) and the Hall mobility (μH ) of bulk-doped rubrene single crystals, which have a band-like nature, are systematically observed. It is found that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.

Organic semiconducting single crystals are perfect for both fundamental and application-oriented research due to the advantages of free grain boundaries, few defects, and minimal traps and impurities, as well as their low-temperature processability, high flexibility, and low cost. Carrier mobilities of greater than 10 cm2 V-1 s-1 in some organic single crystals indicate a promising application in electronic devices. The progress made, including the molecular structures and fabrication technologies of organic single crystals, is introduced and organic single-crystal electronic devices, including field-effect transistors, phototransistors, p-n heterojunctions, and circuits, are summarized. Organic two-dimensional single crystals, cocrystals, and large single crystals, together with some potential applications, are introduced. A state-of-the-art overview of organic single-crystal electronics, with their challenges and prospects, is also provided.

In this paper, we report an efficient alkali metal doping system for organic single crystals. Our system employs an enhanced diffusion method for the introduction of alkali metal into organic single crystals by controlling the sample temperature to induce secondary thermal activation. Using this system, we achieved intercalation of potassium into picene single crystals with closed packed crystal structures. Using optical microscopy and Raman spectroscopy, we confirmed that the resulting samples were uniformly doped and became K2picene single crystal, while only parts of the crystal are doped and transformed into K2picene without secondary thermal activation. Moreover, using a customized electrical measurement system, the insulator-to-semiconductor transition of picene single crystals upon doping was confirmed by in situ electrical conductivity and ex situ temperature-dependent resistivity measurements. X-ray diffraction studies showed that potassium atoms were intercalated between molecular layers of picene, and doped samples did not show any KH- nor KOH-related peaks, indicating that picene molecules are retained without structural decomposition. During recent decades, tremendous efforts have been exerted to develop high-performance organic semiconductors and superconductors, whereas as little attention has been devoted to doped organic crystals. Our method will enable efficient alkali metal doping of organic crystals and will be a resource for future systematic studies on the electrical property changes of these organic crystals upon doping.

Single-Crystal Organic Semiconductors

Developing high-performance polarization-sensitive ultraviolet photodetectors is crucial for their application in military remote sensing, detection, bio-inspired navigation, and machine vision. However, the significant absorption in the visible light range severely limits the application of polarization-sensitive ultraviolet photodetectors, such as high-quality anti-interference imaging. Here, based on a wide-bandgap organic semiconductor single crystal (trans-1,2-bis(5-phenyldithieno[2,3-b:3',2'-d]thiophen-2-yl)ethene, BPTTE), high-performance polarization-sensitive solar-blind ultraviolet photodetectors with a dichroic ratio close to 4.26 are demonstrated. The strong anisotropy of 2D grown BPTTE single crystals in molecular vibration and optical absorption is characterized by various techniques. Under voltage modulation, stable and efficient detection of polarized light is demonstrated, attributed to the intrinsic anisotropy of transition dipole moment in the bc crystal plane, rather than other factors. Finally, high-contrast polarimetric imaging and anti-interference imaging are successfully demonstrated based on BPTTE single crystal photodetectors, highlighting the potential of organic semiconductors for polarization-sensitive solar-blind ultraviolet photodetectors.

The electronic properties of organic single crystals have been intensely studied for well over 40 years. Until recently, organic single-crystal field-effect transistors have generated results that are comparable to and sometimes better in performance than hydrogenated amorphous silicon. Organic thin-film transistors are being actively pursued for a broad area of electronic applications, but their charge-carrier mobilities are limited by structural imperfections (i.e., grain boundaries) and impurities. Organic single crystals, on the other hand, have been limited to charge-transport studies mainly because the fabrication of single-crystal transistors poses a technological challenge. Novel methods for fabricating single-crystal devices include the flip-crystal technique, elastomeric stamp platforms, and freestanding devices, where the source–drain electrodes, dielectric, and gate are all fabricated onto the crystal surface. For the most part, a relatively thick and rigid single crystal is employed (5–500 lm thick). Because the fragility makes them difficult to handle, their use has been restricted to simple and basic devices and wide-ranging applications in sensors or plastic transistors for flexible electronics have not yet been possible. Thus, there is a strong need for the development of mechanically flexible, nondestructive, single-crystal devices with prospective applications in organic electronics while maintaining the intrinsic properties and characteristics of organic single crystals. We demonstrate field-effect transistors fabricated from thin and conformable organic single crystals. We report on proofof-concept “flexible” organic single-crystal field-effect transistors with performance exceeding those of previously reported organic thin-film flexible devices. Rubrene single-crystal devices constructed on low-cost flexible substrates (Fig. 1b) yielded mobilities as high as 4.6 cm V s and on/off ratios of approximately 10.

We report a method to fabricate thin films of large-domain organic semiconductor single crystals dispersed over the whole surface of centimeter-scale substrates for field-effect transistors. Growing less than 500-nm thick film-like organic crystals of sub-millimeter sizes densely in a furnace independently of substrates by physical vapor transport, the collection of the single crystals is mechanically attached to the surface of gate dielectric layers. The organic transistors made of large-domain benzo-annulated pentathienoacene crystals exhibited pronounced transistor performances with mobility values of ∼ 0.2-2 cm2/Vs, which is as high as devices of one-piece crystals. The result demonstrates that the above technique provides a method to apply high performance of organic single crystal transistors to real circuitry devices on large-area substrates.

Distributed feedback lasing from thin organic crystal based on active waveguide grating structures

Investigating the single crystal OFET and photo-responsive characteristics based on an anthracene linked benzo[b]benzo[4,5]thieno[2,3-d]thiophene semiconductor

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron transfer by isolated rhodamine B molecules adsorbed on organic single crystals: a solvent-free model systemKlaus Kemnitz, Nobuaki Nakashima, and Keitaro YoshiharaCite this: J. Phys. Chem. 1988, 92, 13, 3915–3925Publication Date (Print):June 1, 1988Publication History Published online1 May 2002Published inissue 1 June 1988https://doi.org/10.1021/j100324a046RIGHTS & PERMISSIONSArticle Views161Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts