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ConspectusOrganic semiconductors (OSCs) have led to considerable progress in various fields owing to their intrinsic flexibility, adjustable chemical structures, multifunctionalities, and low proce...

Miniaturized organic single-crystal arrays that are addressed by reading-out circuits are crucial for high performance and high-level integration organic electronics. Here, we report a lithography compatible strategy to fabricate organic single-crystal arrays via area-selective growth and solvent vapor annealing (SVA). The organic semiconducting molecules can first selectively grow on photographically patterned drain-source electrodes, forming ordered amorphous aggregates that can further be converted to discrete single-crystal arrays by SVA. This strategy can be applied to self-align the microsized organic single crystals on predesigned locations. With this method, suppression of cross-talk among devices, organic field-effect transistors, and basic logic gate arrays with reading-out electrodes are further demonstrated.

High-resolution scanning tunneling microscopy (STM) is a promising method for characterizing organic semiconductors to obtain a deep understanding of organic semiconductor physics. However, organic films on conductive single-crystal substrates, which are required for STM, usually present different growth behaviors than the films on inert substrates such as SiO2. Here, we reported a simple modification method for modulating the organic semiconductor film growth on the highly oriented pyrolytic graphite (HOPG) and Au(111) substrates and investigated the detailed morphology evolution. Self-assembled monolayers (SAMs) fabricated from vacuum deposition and solution processing were introduced on these conductive substrates. Pentacene, a prototypical organic semiconductor, presented quasi-layer-by-layer growth on HOPG or Au(111) sufaces modified with solution-processed alkane monolayer. The pentacene film resembled the upright packing and terraced morphology but with larger grain size than that of thin-film phas...

A series of nine dipolar merocyanine dyes has been studied as organic semiconductors in transistors and solar cells. These dyes exhibited single-crystal packing motifs with different dimensional ordering, which can be correlated to the performance of the studied devices. Hereby, the long-range ordering of the dyes in staircase-like slipped stacks with J-type excitonic coupling favors charge transport and improves solar cell performance. The different morphologies of transistor thin films and solar cell active layers were investigated by UV-vis, AFM, and XRD experiments. Selenium-containing donor-acceptor (D-A) dimethine dye 4 showed the highest hole mobility of 0.08 cm(2) V(-1) s(-1). BHJ solar cells based on dye 4 were optimized by taking advantage of the high crystallinity of the donor material and afforded a PCE of up to 6.2%.

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

Weak epitaxy growth (WEG) is an effective method in the preparation of high-mobility thin films of disk-like organic semiconductors. The growth behavior and quality of the epitaxial thin film are closely related to the inducing layers. Here, a series of fluorinated molecules, 5,5"-bis(3'-fluoro-biphenyl-4-yl)-2,2':5',2"-terthiophene (m-F2BP3T), 5,5"-bis(3',5'-difluoro-biphenyl-4-yl)-2,2':5',2"-terthiophene (F4BP3T), and 5,5"-bis(4'-fluoro-biphenyl-4-yl)-2,2':5',2"-terthiophene (p-F2BP3T) as well as a referenced molecule 5,5"-bis(biphenyl-4-yl)-2,2':5',2"-terthiophene (BP3T), are introduced to serve as inducing layers for the epitaxy growth of phthalocyanine. Compared to the nonfluorinated inducing layer, the interactions between the fluorinated inducing layer and phthalocyanine might be relatively strong due to the potential existence of C-H···F weak hydrogen bonds. The growth behavior and mechanism of phthalocyanine on the fluorinated inducing layers are investigated by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXD), selected area electron diffraction (SAED). According to the AFM and SAED, H(2)Pc presents a selective epitaxy growth depending on the position of fluorine: epitaxy growth on m-F2BP3T and F4BP4T, and nonepitaxy growth on p-F2BP3T. Comparison of CuPc with F(16)CuPc on monolayer p-F2BP3T further revealed that the uncommon nonepitaxy growth behavior of H(2)Pc (CuPc) on p-F2BP3T mainly originates from the enhanced interactions between the two types of molecules. As a consequence, the capability of molecules orienting themselves along the surface channel is decreased; meanwhile, the demand of the upper limit of the lattice mismatch is more rigorous for commensurate epitaxy. Finally, the oriented nucleation of H(2)Pc (CuPc) on monolayer p-F2BP3T is affected, and netlike crystals are formed. The sudden change of H(2)Pc (CuPc) from multiorientation on monolayer to just one orientation on double-layer p-F2BP3T suggests that there is a critical lattice mismatch value for commensurate epitaxy in WEG when the molecule-substrate interactions are enhanced.

Evolution of BP2T films grown at the early stage was investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). The AFM results demonstrate that the BP2T grown on the SiO2 substrate transformed from a layer by layer growth to island growth when the coverage is higher than 3 ML. The out-of-plane and in-plane X-ray diffraction measurements reveal a phase transition from the thin film phase to the bulk phase suddenly occurs as the growth mode changes. A careful analysis of the structure evolution implies that not only the strain but also the soft matter property of the organic thin films are responsible for the thickness dependent evolution. Moreover, the thickness dependent structure and phase of BP2T films result in different morphologies of ZnPc grown on different layers of BP2T. The ZnPc crystals gradually changed from stripe-like to nanofiber-like, concomitantly with the epitaxy relationships from incommensurate epitaxy to commensurate epitaxy. Conversely, the diversity of ZnPc films also reflects different properties of the BP2T films with different numbers of layer, which cannot be obtained from the AFM or XRD. This study supplies a deeper insight into the thickness evolution of organic thin films and to the weak epitaxy growth.