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While great progress has been achieved in the research of various solution-processed organic semiconductors, the randomized crystal orientations and charge carrier mobility variations have posed tremendous challenges to implement the organic semiconductors for organic electronic device applications. Among the miscellaneous polymer additives reported to tune the crystal growth and modulate charge transport, poly(α-methyl styrene) (PαMS) has been extensively studied for its capability to improve semiconductor crystallization, reduce bulk crystal misorientation, induce phase segregation, enhance morphological uniformity and boost electrical performance of organic thin film transistors and organic electronic devices. In the first section of this article, we review the recent progress of organic electronics and highlight the crystal misorientation and mobility variation as the challenges that need to be overcome. Then, the various merits from mixing polymeric additives with organic semiconductors are discussed. In the second section, we provide an overview of the previous works that employ PαMS for regulating the crystal orientation alignment and modulating charge transport of miscellaneous solution-processed small-molecular organic semiconductors including 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) and 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TESADT). By discussing these important examples, we intend to demonstrate that PαMS can be versatilely implemented to improve other new organic semiconductor crystallization and mobility for high-performance organic electronic applications. [ABSTRACT FROM AUTHOR]

In this work, we report for the first time the combination of silicon dioxide (SiO2) nanoparticles and poly (styrene-block-4-vinylpyridine) (PS-b-P4VP) block copolymer supplements to tune random crystal growth and improve charge transport of small-molecule organic semiconductors. We chose 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) as a model semiconductor material to combine with both supplements. This led to a rigid alignment of the crystals that extended in long-range order as well as an increased coverage of the charge transport channel. In particular, the addition of 5% PS-b-P4VP supplement contributed to a low irregularity angle of 8.8° ± 6.7°, which indicates an 80% reduction of crystal random orientation. Bottom-gate, top-contact organic thin film transistors (OTFTs) based on the TIPS-PEN/SiO2/PS-b-P4VP combination film showed an average hole mobility of up to 0.033 ± 0.02 cm2/Vs and a 50% improvement of charge transport fidelity. The improved charge transport of TIPS-PEN crystals can be ascribed to both increased channel coverage due to the uniformity property of PS-b-P4VP polymer, and an effective nanoscale confinement of the random crystal growth due to the aggregation of nanoparticles. The facile method we reported in this work can be applied to manipulate the crystal growth and charge transport of the general solution-processed, small-molecule semiconductors for high-fidelity organic electronics applications on flexible substrate. [ABSTRACT FROM AUTHOR]

In this study, we showcase the use of silicon dioxide (SiO2) nanoparticles and hexamethyldisilazane (HMDS) treatment to regulate the thin film morphology and manipulate charge transport of solution-processed, small-molecular, organic semiconductors. 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was blended with SiO2 nanoparticles as an exemplary organic semiconductor. A higher concentration of SiO2 nanoparticles were observed near the edge of TIPS pentacene crystals and enlarged the width of crystal edges. This greatly reduced the dendritic crystal growth pattern of TIPS pentacene and contributed to its enhanced orientation uniformity. In addition, the HMDS treatment effectively passivated the silanol groups on the hydrophilic gate dielectrics. As a result, bottom-gate, top-contact TIPS pentacene/SiO2 nanoparticle-based organic thin-film transistors boosted a performance consistency enhancement (defined by the ratio of average mobility to the standard deviation of mobility). The combinational approach to employ SiO2 nanoparticles and HMDS treatment as demonstrated in this work sheds light on important applications in high-performance organic electronics devices on flexible substrate. [ABSTRACT FROM AUTHOR]

In this study, we report that the vertical phase separation between a small-molecule organic semiconductor and a polymer additive can be utilized to drive semiconductor crystallization, enhance thin film morphology, and improve device performance of solution-processed organic thin film transistors (OTFTs). When 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was demonstrated as a benchmark semiconductor material to blend with a polyacrylate polymer additive poly(2-ethylhexyl acrylate) (P2EHA), it was found that a vertical phase segregation occurred between TIPS pentacene and P2EHA, providing a confinement of anisotropic semiconductor crystallization and resulting in an elevated TIPS pentacene concentration at the charge transport interface. Accordingly, distinctive TIPS pentacene thin film morphology in terms of areal coverage, grain width, and crystal orientation was obtained by varying the loading ratio of the P2EHA polymer additive. Bottom-gate and bottom-contact OTFTs were fabricated to test charge transport and a hole mobility of up to 0.27 cm2/Vs was demonstrated with 80% loading ratio of P2EHA. The effective experimental method and important results as we showcased in this work can be applied to drive crystallization and optimize film morphology of small-molecule organic semiconductors other than TIPS pentacene. [ABSTRACT FROM AUTHOR]

In this work, we report for the first time the use of a nonconjugated semicrystalline polymer as a film-forming agent to control the crystallization and tune the charge transport of solution-processed, small-molecule organic semiconductors. When 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS pentacene) was demonstrated as a representative material to blend with polyethylene oxide (PEO) polymer, it crystallized into uniformly-aligned needles with reduced random orientation, enhanced long-range order and elevated areal coverage. Specifically, an ultra-low misorientation angle of 7.9° ± 3.5° was obtained with 10% PEO additive, beneficial for charge transport in the TIPS pentacene/PEO hybrid film. Bottom-gate, top-contact organic thin film transistors (OTFTs) based on TIPS pentacene/PEO mixture were found to show a field-effect mobility up to 2.5 × 10−2 cm2/Vs. This work may be universally applied to other organic semiconductors to regulate their crystal formation, enhance film forming and improve device performance of OTFTs. It contributes to the utilization of flexible substrates for future-generation high-performance organic electronics. [ABSTRACT FROM AUTHOR]

Although much research progress has recently been achieved in solution-soluble, small-molecule, organic semiconductors, their randomly oriented crystals still remain as an issue that leads to nonuniform charge transport and severely degrades performance consistency of organic thin film transistors (OTFTs). In the paper, we reviewed the various small-molecule additives that have been reported to blend with these semiconductors in order to reduce their crystal misorientation and mobility variations of OTFTs. By mainly studying the examples of a representative small-molecule organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene, we intend to disclose the important effects of the various additives on controlling the semiconductor crystallization, film morphology, and charge transport. This work can be facilely employed to align the crystal orientation and tweak the electrical performance of newly discovered small-molecule organic semiconductors, and will provide an in-depth understanding of the important application in high-performance, solution-based, large-area organic electronics devices. [ABSTRACT FROM AUTHOR]

The electrical performance of solution-processed, small-molecule organic semiconductors is largely restricted by their severe charge carrier mobility variations. In this work, we demonstrate an effective method to reduce such variations of the semiconductor mobilities and improve the performance consistency of organic thin film transistors (OTFTs) by adding poly(α-methylstyrene) (PαMS) as a polymer additive. By using 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) as an example, we found that while pristine TIPS pentacene film exhibited random crystal orientation and large film gaps, the addition of PαMS polymer promoted the growth of semiconductor crystals, which formed uniformly aligned needles with significantly improved orientation and coverage within the channel regions. An ultra-low misorientation angle of 2.2° ± 1° was obtained from TIPS pentacene/PαMS blend film, which is a 20-fold reduction as compared to pristine TIPS pentacene. Bottom-gate, top-contact OTFTs with TIPS pentacene crystals aligned perpendicularly from source to drain contact electrodes demonstrated a hole mobility of up to 0.26 cm2/V s, as well a 6-fold enhancement of average mobility as compared to the pristine TIPS pentacene based counterparts. Notably, the addition of PαMS led to a performance consistency factor of 3.35, as defined by the ratio of the average mobility to standard deviation, implying a great reduction of charge carrier mobility variations. The improvement of electrical performance of OTFTs can be attributed to the combined outcome of crystal rigid alignment, extended long-range order, and almost full coverage of charge transport channel. [ABSTRACT FROM AUTHOR]

In this work, we study for the first time the effect of a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer to control the crystal growth of solution-processed, small-molecule organic semiconductors and to improve the device performance of organic thin film transistors (OTFTs). A benchmark semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was employed to blend with the polymer additive. The TIPS pentacene blend film with 5% PVDF-HFP by weight ratio exhibited a significant morphology enhancement with crystals strictly aligned in long-range order. In particular, it showed an average grain width of 69.98 μm and a misorientation angle of 6.6°, which is a 3.5-fold increase and a 7-fold reduction as compared to the pristine TIPS pentacene film. The bottom-gate, top-contact TIPS pentacene OTFTs with PVDF-HFP polymer additive were fabricated. Electrical characterization showed a hole mobility of up to 0.1 cm2/Vs with 5% PVDF-HFP. The performance improvement of TIPS pentacene/PVDF-HFP based OTFTs can be attributed to the reduced amount of charge trap centers at the enlarged grain width, alleviated crystal misorientation and increased areal coverage. This facile approach to blend PVDF-HFP additive to align crystals and improve orientation in long-range order as demonstrated in this work can be useful for controlling the crystallization and charge transport of other small-molecule organic semiconductors for application in organic electronics on large-scale flexible substrate. [ABSTRACT FROM AUTHOR]