Crystallization from a Droplet: Single-Crystalline Arrays and Heterojunctions for Organic Electronics

General Spatial Confinement Recrystallization Method for Rapid Preparation of Thickness-Controllable and Uniform Organic Semiconductor Single Crystals

Organic semiconductor single crystals (OSSCs) are ideal materials for studying the intrinsic properties of organic semiconductors (OSCs) and constructing high-performance organic field-effect transistors (OFETs). However, there is no general method to rapidly prepare thickness-controllable and uniform single crystals for various OSCs. Here, inspired by the recrystallization (a spontaneous morphological instability phenomenon) of polycrystalline films, a spatial confinement recrystallization (SCR) method is developed to rapidly (even at several second timescales) grow thickness-controllable and uniform OSSCs in a well-controlled way by applying longitudinal pressure to tailor the growth direction of grains in OSCs polycrystalline films. The relationship between growth parameters including the growth time, temperature, longitudinal pressure, and thickness is comprehensively investigated. Remarkably, this method is applicable for various OSCs including insoluble and soluble small molecules and polymers, and can realize the high-quality crystal array growth. The corresponding 50 dinaphtho[2,3-b:2″,3″-f]thieno[3,2-b]thiophene (DNTT) single crystals coplanar OFETs prepared by the same batch have the mobility of 4.1 ± 0.4 cm2 V-1 s-1 , showing excellent uniformity. The overall performance of the method is superior to the reported methods in term of growth rate, generality, thickness controllability, and uniformity, indicating its broad application prospects in organic electronic and optoelectronic devices.

Long-Range Ordered Organic Bulk-Heterojunction: C60 and O-IDTBR Single Crystals Penetrated by Crystalline P3HT Fibrous Networks

The long-range ordering of bulk-heterojunctions (BHJs) significantly facilitates exciton diffusion and dissociation as well as charge transport. A feasible bio-inspired strategy to realize such a heterostructure is crystallization in gel media where the growing host crystals incorporate the surrounding guest materials of gel networks. Until now, the host-guest pairs forming ordered BHJs are still very limited and, more importantly, the used gel-network guests are structurally amorphous, spurring investigation toward crystalline gel-networks. Here, single crystals of fullerene and non-fullerene acceptors (NFAs) in poly(3-hexylthiophene) (P3HT) organogel are prepared, forming C₆₀ :P3HT and (5Z,5″Z)-5,5″-((7,7″-(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b″]dithiophene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole-7,4-diyl))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one) (O-IDTBR):P3HT BHJs. The crystalline P3HT network penetrates the crystal matrix without significantly disturbing the single crystallinity, resulting in long-range ordered BHJs. This bi-continuous structure, together with an improved overall ordering, contributes to enhanced charge/energy transfer. As a result, photodetectors based on these ordered BHJs exhibit ameliorated responsivity, detectivity, bandwidth, and stability as compared to the conventional BHJs with short-range ordering. Therefore, this work further extends the scope of long-range ordered BHJs toward crystalline polymer donors and NFAs, providing a generally applicable strategy for the design of organic optoelectronic devices with superior performance.

Dielectric behavior of curcuminoid polymorphs on different substrates by direct soft vacuum deposition

Our work examines the structural-electronic correlation of a new curcuminoid, AlkCCMoid, as a dielectric material on different substrates. For this purpose, we show a homemade sublimation method that allows the direct deposition of molecules on any type of matrix. The electronic properties of AlkCCMoid have been evaluated by measurements on single crystals, microcrystalline powder, and sublimated samples, respectively. GIWAXS studies on surfaces and XRD studies on powder have revealed the existence of polymorphs and the effect that substrates have on curcuminoid organization. We describe the dielectric nature of our system and identify how different polymorphs can affect electronic parameters such as permittivity, all corroborated by DFT calculations.

Crystal structure of the cocrystal 2,4,6-triamino-1,3,5-triazine – 1H-isoindole-1,3(2H)-dione – methanol (1/1/1), C12H15N7O3

C12H15N7O3, P21/c (no. 14), a = 7.1782(3) Å, b = 16.6800(6) Å, c = 12.1070(5) Å, β = 92.030(2)°, V = 1448.69(10) Å3, Z = 4, Rgt (F) = 0.0449, wRref (F 2) = 0.1220, T = 296(2) K.

Recent Advances in Realizing Highly Aligned Organic Semiconductors by Solution-Processing Approaches

Solution-processing approaches are widely used for controlling the aggregation structure of organic semiconductors because they are fast, efficient, and have strong practicability. Effective regulation of the aggregation structure of molecules to achieve highly ordered molecular stacking is key to realizing effective carrier transport and high-performance devices. Numerous studies have achieved highly aligned organic semiconductors using different solution-processing approaches. This article provides a detailed review of the prevalent solution-processing technologies and emerging methods developed over the past few years for the alignment of organic semiconducting materials. These technologies and methods are classified according to the processing principle. This review focuses on the principles of different experimental techniques, improvements upon the conventional methods, and state-of-the-art performance of resulting devices. In addition, a brief discussion of the characteristics and development prospects of various methods is presented.

Challenging Bendable Organic Single Crystal and Transistor Arrays with High Mobility and Durability toward Flexible Electronics

Bendable organic single crystals are promising candidates for flexible electronics owing to their superior charge-transport properties. However, large-area high-quality organic single crystals are rarely available on the polymer substrates generally used in flexible electronics. Here, a surface-assisted assembly strategy based on a polymer modification, poly(amic acid) (PAA), is developed to grow large-area organic singe crystals on polymer substrates using a simple drop-casting method. The unique surface properties of PAA that enable molecular solution superwetting and promote molecular ordered assembly produce an extraordinary self-driven "meniscus-guided coating" behavior, enabling the fabrication of millimeter-sized, highly aligned organic single crystals for a variety of organic semiconductors. Organic field-effect transistors based on a mode molecule of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene demonstrate the highest (average) mobility of 18.6 cm² V^-1 s^-1 (15.9 cm² V^-1 s^-1 ), attractively low operating voltage of -3 V, and high flexible durability. The results shed light on the large-area fabrication of organic single crystals on polymer dielectrics toward high-performance and integrated plastic electronics.