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In this study, we demonstrated for the first time that a metal-containing semicrystalline polymer was used as an additive to mediate the thin film morphology of solution-grown, small-molecule organic semiconductors. By mixing polyferrocenylsilane (PFS) with an extensively-studied organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene), PFS as a semicrystalline polymer independently forms nucleation and crystallization while simultaneously ameliorating diffusivity of the blend system and tuning the surface energies as a result of its partially amorphous property. We discovered that the resultant blend film exhibited a 6-fold reduction in crystal misorientation angle and a 3-fold enlargement in average grain width. Enhanced crystal orientationmore » considerably reduces mobility variation, while minimized defects and trap centers located at grain boundaries lessen the adverse impact on the charge transport. Consequently, bottom-gate, top-contact organic thin film transistors (OTFTs) based on the TIPS pentacene/PFS mixture yielded a 40% increase in performance consistency (represented by the ratio of average mobility to the standard deviation of mobility). The PFS semicrystalline polymer-controlled crystallization can be used to regulate the thin film morphology of other high-performance organic semiconductors and shed light on applications in organic electronic devices.« less

In this study, we report an efective approach to tune the crystallization, microstructure and charge transport of solution-processed organic semiconductors by blending with a conjugated polymer additive poly(3-hexylthiophene) (P3HT). When 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was used as a model semiconductor material to mix with diferent amount of P3HT, their intermolecular interactions led to distinctive TIPS pentacene flm morphologies, including randomly-oriented crystal ribbons, elongated needles with enhanced long-range order, and grasslike curved microwires with interlinkages. Each type of morphology was found to further correlate to considerably diferent charge transport and device performance. As compared to pristine TIPS pentacene devices, bottom-gate, top-contactmore » OTFTs with 2% in weight P3HT additive showed a 2-fold and 5-fold improvement of average feld-efect mobility and performance consistency (defned as the ratio of average mobility to the standard deviation), respectively. The improvement in transistor electrical performance can be attributed to the combined efect of enhanced crystal orientation and uniformity, as well as increased areal coverage. This work can be applied beyond the particular example demonstrated in this study and to tune the charge transport of other small-molecule organic semiconductors in general.« less

Organic electronics devices based on high-performance small-molecule organic semiconductors have gained substantial attention because of their unique advantages such as excellent charge transport, solution processability, and environmental stability. However, the intrinsic crystallization of small-molecule organic semiconductors is anisotropic, resulting in significant device performance variations of organic electronics devices. In this article, the authors review the various approaches and techniques developed to control and align the crystallization of some benchmark solution-processable, high-performance, small-molecule organic semiconductors, such as 6,13-bis(triisopropylsilylethynyl) pentacene, N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide, and 5,11-bis(triethylgermylethynyl)anthradithiophene. These alignment approaches are studied in the context of capillary force-based techniques, patterning-based techniques, solution-shearing-based techniques, and othermore » miscellaneous techniques, including zone-casting, vertical flowing, air flow navigation, temperature gradient alignment, etc. The organic semiconductors and crystal alignment techniques reviewed in this article shed light on important relationship among crystallization, charge transport, and device performance and can be applied to various high-performance organic electronics devices, such as organic thin film transistors and solar cells.« less

Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5"-n-hexyl-2,2',5',2"]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10^-2 cm²/V s, which is themore » highest mobility from SMDPPEH ever reported.« less

N,N⁰-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN₂) is an n-type semiconductor exhibiting high electron mobility and excellent air stability. However, the reported electron mobility based on spin-coated PDIF-CN₂ film is much lower than the value of PDIF-CN₂ single crystals made from vapor phase deposition, indicating significant room for mobility enhancement. In this study, various insulating polymers, including poly(vinyl alcohol), poly(methyl methacrylate) (PMMA), and poly(alpha-methylstyrene) (PaMS), are pre-coated on silicon substrate aiming to enhance the morphology of the PDIF-CN₂ thin film, thereby improving the charge transport and air stability. Atomic force microscopy images reveal that with the pre-deposition of PaMS or PMMA polymers, the morphologymore » of the PDIF-CN₂ polycrystalline films is optimized in semiconducting crystal connectivity, domain size, and surface roughness, which leads to significant improvement of organic thin-film transistor (OTFT) performance. Particularly, an electron mobility of up to 0.55 cm²/V s has been achieved from OTFTs based on the PDIF-CN₂ film with the pre-deposition of PaMS polymer.« less