Large-Size Single-Crystal Oligothiophene-Based Monolayers for Field-Effect Transistors

Abstract

High structural quality of crystalline organic semiconductors is the basis of their superior electrical performance. Recent progress in quasi two-dimensional (2D) organic semiconductor films challenges bulk single crystals because both demonstrate competing charge-carrier mobilities. As the thinnest molecular semiconductors, monolayers offer numerous advantages such as unmatched flexibility and light transparency as well they are an excellent platform for sensing. Oligothiophene-based materials are among the most promising ones for light-emitting applications because of the combination of efficient luminescence and decent charge-carrier mobility. Here, we demonstrate single-crystal monolayers of unprecedented structural order grown from four alkyl-substituted thiophene and thiophene–phenylene oligomers. The monolayer crystals with lateral dimensions up to 3 mm were grown from the solution on substrates with various surface energies and roughness by drop or spin-casting with subsequent slow solvent evaporation. Our data indicate that 2D crystallization resulting in single-crystal monolayers occurs at the receding gas–solution–substrate contact line. The structural properties of the monolayers were studied by grazing-incidence X-ray diffraction/reflectivity, atomic force and differential interference contrast microscopies, and imaging spectroscopic ellipsometry. These highly ordered monolayers demonstrated an excellent performance in organic field-effect transistors approaching the best values reported for the thiophene or thiophene–phenylene oligomers. Our findings pave the way for efficient monolayer organic electronics highlighting the high potential of simple solution-processing techniques for the growth of large-size single-crystal monolayers with excellent structural order and electrical performance competing against bulk single crystals.

Surface-Enhanced Raman Spectroscopy of 2D Organic Semiconductor Crystals

“…These ranges were found empirically to maximize the SERS signal-to-noise ratio (see Section 1 of the Supporting Information). DD-TTPTT and DH-TTPTT molecules were synthesized and characterized as described in ref . DH-TTPTT and DD-TTPTT films were grown on the SERS substrates by drop casting from toluene solutions (0.15 g/L) with subsequent slow solvent evaporation and characterized with circular polarized light-differential interference contrast (C-DIC) microscopy .…”

“…Large area single-crystal organic ultrathin films whose thickness is between one and a few molecular monolayers are a novel promising class of two-dimensional (2D) materials for flexible transparent ultrathin electronics. High structural quality of the organic semiconductor 2D single crystals resulted in charge-carrier mobilities competing with those of high-quality bulk crystals. − As the electrical current in organic field-effect transistors (OFETs) flows within a few nanometer thick active layer of the semiconductor, , the use of ultrathin films can significantly reduce the material consumption without losing device performance. Moreover, 2D organic semiconductors offer promising opportunities for efficient sensing , and light emitting devices …”

“…Although some authors reported TEM studies of the crystallinity in 2D organic semiconductors and the corresponding unit cell parameters, , this technique is very challenging for monolayers because of their rapid degradation under the electron beam . Grazing incident X-ray diffraction (GIXD) can be also used to study 2D organic semiconductors. , For example, the recent GIXD study on monolayers of thiophene–phenylene co-oligomers (TPCO) revealed the unit cell parameters in millimeter-size monolayer single crystals. However, even by using the state-of-the-art synchrotron-based GIXD technique, full resolution of the 2D crystal structure (i.e., determination of atom positions) have not yet been achieved.…”

Highly luminescent crystals of a novel linear π-conjugated thiophene–phenylene co-oligomer with a benzothiadiazole fragment

“…Thus, methods of growth from solutions remain the most promising for the preparation of high-quality single crystals of cooligomers with a significant molecular weight. The following growth methods were used: the vapour diffusion method, slow isothermal solvent evaporation, slow isochoric solvent cooling (Postnikov et al, 2014) and growth on glass substrates under slow isothermal solvent drying (Bruevich et al, 2019;Cao et al, 2019). The results of co-oligomer (TMS-2T-Ph) 2 -BTD crystal growth using each of these methods are discussed below.…”

Анизотропия Роста И Структура Кристаллов Линейных Сопряженных Олигомеров

“…Для получения сравнительно крупных монокристаллических образцов наиболее привлекательными с точки зрения простоты и малой затратности являются методы роста кристаллов из растворов [5][6][7][8]. Растворные техники роста кристаллов также являются перспективными для технологии формирования ультратонких монокристаллических пленок полупроводниковых олигомеров непосредственно на подложках в условиях медленного высыхания растворителя [9]. Однако, если одни вещества склонны к формированию обширных монокристаллических пленок в процессе роста на межфазных границах, то для других этого не удается осуществить в силу расположенности их к росту в виде игольчатых кристаллов.…”