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Abstract

Polymer conductors that are solution processable provide an opportunity to realize low-cost organic electronics. However, coating sequential layers can be hindered by poor surface wetting or dissolution of underlying layers. This has led to the use of transfer printing where solid film inks are transferred from a donor substrate to partially fabricated devices using a stamp. This approach typically requires favorable adhesion differences between the stamp, ink, and receiving substrate. Here, we present a shear-assisted organic printing (SHARP) technique that employs a shear load on a post-less polydimethylsiloxane (PDMS) elastomer stamp to print large-area polymer films that can overcome large unfavorable adhesion differences between the stamp and receiving substrate. We explore the limits of this process by transfer printing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films with varied formulation that tune adhesive fracture energy. Using this platform, we show that the SHARP process is able to overcome a 10-fold unfavorable adhesion differential without the use of a patterned PDMS stamp enabling large area printing. The SHARP approach is then used to print PEDOT:PSS films in the fabrication of high performance semitransparent organic solar cells.

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... The most common implementation of microtransfer printing uses a compliant elastomer stamp to retrieve and print thin components. Microtransfer printing allows microstructures and devices fabricated in different processes to be integrated with one another or onto unconventional substrates, enabling the fabrication of flexible electronics ( Meitl et al., 2006 ;Kim et al., 2010 ;Carlson et al., 2012 ), advanced photovoltaic cells ( Sen et al., 2018 ) and 3D microstructures ( Ahn et al., 2006 ). Mechanics plays a central role in the success of microtransfer printing processes as delamination at specific interfaces must be realized in different steps of the process. ...
... Inflatable stamps and subsurface pressure have been applied to deform the stamp and induce an interfacial stress distribution that facilitates printing Linghu et al., 2019 ). Finally, Carlson et al. (2011) , Minsky andTurner (2017) and Sen et al. (2018) exploited a different loading configuration, namely an applied lateral (i.e. shear) load on the top of the stamp, which produces a moment on the interface and generates a large stress at one edge of the stamp-chip interface to facilitate detachment in the printing step. ...
... This stamp geometry is not often used as it does not allow selective retrieval of components, but it is feasible and has been used in some reports of microtransfer printing (e.g. Meitl et al., 2006 ;Sen et al., 2018 ). ...
Article
Microtransfer printing is a manufacturing technique that relies on controlled selective delamination between two interfaces to transfer thin solid films and chips. Stamps in these processes are often designed to leverage strategies that modify the interfacial stress distribution at the stamp interface to achieve a specific adhesion response, however the effect of a modified stress distribution at the stamp interface on crack path selection between the two interfaces in the system is unclear. This paper investigates how the stress distribution beneath the stamp can affect the delamination path between the two interfaces in a microtransfer printing process using mechanics modeling. In general, altering the stress distribution at the stamp/chip interface also alters the stress distribution at the chip/substrate interface. For a sufficiently thin chip with no or small initial defects at the interfaces, the common approach of tuning adhesion by reducing the strength of stress singularity near the edge of the stamp does not provide a robust route to control the delamination path. An alternative stamp design strategy, guided by the singularity order of the stress distribution, is proposed and analyzed. In the proposed stamp design, the delamination path can be controlled through the stamp thickness and the application of a shear displacement. This work provides a fundamental understanding of the mechanics of the microtransfer printing process as well guidance for designing successful microtransfer printing processes.
... Therefore, the controllable seal adhesion force is a hot topic in microtransfer printing technology. Most researchers control the adhesion of elastic seals through the separation speed of the seal interface, the loading method, the microstructure of the sealing surface, and the temperature of the seal, which gives birth to the following microtransfer printing methods: kinetic control transfer printing [37,48,70,71,[78][79][80], laser control seal temperature transfer printing [4,39,57,59,68,74,81], microstructure seal to assist in transfer printing [60][61][62]82], transfer printing with applied shear load [73,83,84], tape-assisted transfer printing [76,77], transfer printing with a seal inflatable [85], and magnetic control transfer printing [56,72]. ...
... It can be seen that the increase in shear strain can effectively reduce the stripping force of the interface, thereby reducing the adhesion force of the seal/device interface, to realize the transfer printing. Brendan et al. [83] improved the transfer printing technology that applied shear load and used this method to manufacture organic photovoltaic cells. This technology broke through the difficulty of printing relatively soft and large-area polymer films. ...
Article
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In recent years, with the rapid development of the flexible electronics industry, there is an urgent need for a large-area, multilayer, and high-production integrated manufacturing technology for scalable and flexible electronic products. To solve this technical demand, researchers have proposed and developed microtransfer printing technology, which picks up and prints inks in various material forms from the donor substrate to the target substrate, successfully realizing the integrated manufacturing of flexible electronic products. This review retrospects the representative research progress of microtransfer printing technology for the production of flexible electronic products and emphasizes the summary of seal materials, the basic principles of various transfer technology and fracture mechanics models, and the influence of different factors on the transfer effect. In the end, the unique functions, technical features, and related printing examples of each technology are concluded and compared, and the prospects of further research work on microtransfer printing technology is finally presented.
... Transfer printing is capable of transferring various classes of materials with a wide range of geometries and configurations (referred to as ink) from one substrate (referred to as the donor) to another via a stamp and has been extensively used for flexible and stretchable electronics 1 , such as bendable transistors 2 , stretchable nanophotonic devices 3 , stretchable radio frequency identification tags 4 , and flexible photodetectors 5 . While a variety of transfer printing methods have been developed [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] , the resolution of most of these methods, that is, the narrowest continuous line that can be reliably transferred, is at the micrometer scale. There are a few methods that allow the transfer of nanoscale patterns 19,20 . ...
Article
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Transfer printing is an emerging assembly technique for flexible and stretchable electronics. Although a variety of transfer printing methods have been developed, transferring patterns with nanometer resolution remains challenging. We report a sacrificial layer-assisted nanoscale transfer printing method. A sacrificial layer is deposited on a donor substrate, and ink is prepared on and transferred with the sacrificial layer. Introducing the sacrificial layer into the transfer printing process eliminates the effect of the contact area on the energy release rate (ERR) and ensures that the ERR for the stamp/ink-sacrificial layer interface is greater than that for the sacrificial layer/donor interface even at a slow peel speed (5 mm s −1). Hence, large-area nanoscale patterns can be successfully transferred with a yield of 100%, such as Au nanoline arrays (100 nm thick, 4 mm long and 47 nm wide) fabricated by photolithography techniques and PZT nanowires (10 mm long and 63 nm wide) fabricated by electrohydrodynamic jet printing, using only a blank stamp and without the assistance of any interfacial chemistries. Moreover, the presence of the sacrificial layer also enables the ink to move close to the mechanical neutral plane of the multilayer peel-off sheet, remarkably decreasing the bending stress and obviating cracks or fractures in the ink during transfer printing.
... Moreover, the charge and discharge capacities of Li 2 NiF 4 -PEDOT cathode material are observed to be 400 mAh g -1 and 7%, respectively. These are very near to standard value; therefore, the determined columbic efficiency is 72%, and this value is greater than the translation electrodes [56]. ...
... There has been growing demand for electronic textiles (E-textiles) that combine clothes and multi-functional electronics [1][2][3]. E-textiles are intrinsically designed to be equipped with wearable and portable electronic technologies, and their comfortable and light-weight characteristics afford unsurpassed electronic applications in the field of healthcare, energy, bioelectronics, and smart clothing [4][5][6][7][8][9][10][11][12][13][14]. Recent advances in E-textiles have developed numerous materials/engineering technologies for flexible conductors, most of which focus on incorporating conductive materials such as metallic nanomaterials, carbon materials, or thin metal layers in elastomers [15][16][17]. ...
Article
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To enable highly conductive electronic textiles (E-textiles), we herein demonstrate a simple solution treatment of poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS)-coated textiles by dimethyl sulfoxide (DMSO) and methanol. The subsequent solution engineering of DMSO and methanol not only enhances crystallization of PEDOT chains but also the contact for PEDOT:PSS to the fibers. Additionally, the methanol dipping effectively removes the insulating PSS part from the conductive PEDOT chains, which contributes to subsequently reduced sheet resistance of less than 3 Ω/sq of the conductive textiles. Joule heating property of the highly conductive textiles achieves the maximum temperature with the temperature reaching 133 °C at a low applied voltage of 3 V within 20 s, which promises highly conductive E-textiles as multi-functional wearable heater applications.
... The nanopolystyrene (NPS) has been frequently used as an example to determine the potential nanoplastic toxicity in organisms. The polystyrene particles have the potential to be used in at least food containers, packaging, textiles, and adhesive (Abdallah et al., 2018;Sen et al., 2018;Gelbke et al., 2019). ...
Article
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The underlying mechanisms of microRNAs (miRNAs) in regulating nanoplastic toxicity are still largely unclear in organisms. In nanopolystyrene (NPS) exposed Caenorhabditis elegans, the expression of mir-76 (a neuronal miRNA) was significantly decreased, and the mir-76 mutant was resistant to the toxicity of NPS. The aim of this study was to determine the molecular basis of mir-76 in controlling NPS toxicity in nematodes. The mir-76 mutation increased expression of glb-10 encoding a globin protein in NPS (1 μg/L) exposed nematodes. Exposure to NPS (1–100 μg/L) increased the glb-10 expression, and the glb-10(RNAi) worm was susceptible to NPS toxicity in inducing reactive oxygen species (ROS) production and in decreasing locomotion behavior. Using ROS production and locomotion behavior as endpoints, mutation of glb-10 inhibited resistance of mir-76 mutant to NPS toxicity, and neuronal overexpression of mir-76 inhibited the resistance to NPS toxicity in nematodes overexpressing neuronal glb-10 containing 3’ untranslated region (3’UTR). Thus, GLB-10 functioned as a target of mir-76 in the neurons to regulate the NPS toxicity. Moreover, a signaling cascade of HRG-7-HRG-5 required for the control of heme homeostasis was identified to function downstream of neuronal GLB-10 to regulate the NPS toxicity. In this signaling cascade, the neuronal HRG-7 regulated the NPS toxicity by antagonizing function of intestinal HRG-5. Furthermore, in the intestine, HRG-5 controlled NPS toxicity by inhibiting functions of hypoxia-inducible transcriptional factor HIF-1 and transcriptional factor ELT-2. Our results highlight the crucial function of heme homeostasis related signaling in regulating the NPS toxicity in organisms.
... While we scan opposite sides of the film with this process, we find that the film quality is roughly equivalent, consistent with our previous demonstrations of transfer printed polymer semiconductors. 52,53 Finally, the source−drain electrodes that consist of the Ag NW/PDMS composite were removed from its donor quartz substrate and laminated onto the polymer semiconductor layer. ...
Article
Stretchable electronics are poised to revolutionize personal healthcare and robotics, where they enable distributed and conformal sensors. Transistors are fundamental building blocks of electronics, and there is a need to produce stretchable transistors using low-cost and scalable fabrication techniques. Here, we introduce a facile fabrication approach using laser patterning and transfer printing to achieve high-performance, solution-processed intrinsically stretchable organic thin-film transistors (OTFTs). The device consists of Ag nanowire (NW) electrodes, where the source and drain electrodes are patterned using laser ablation. The Ag NWs are then partially embedded in a poly(dimethylsiloxane) (PDMS) matrix. The electrodes are combined with a PDMS dielectric and polymer semiconductor, where the layers are individually transfer printed to complete the OTFT. Two polymer semiconductors, DPP-DTT and DPP-4T, are considered and show stable operation under the cyclic strain of 20 and 40%, respectively. The OTFTs maintain electrical performance by adopting a buckled structure after the first stretch-release cycle. The conformability and stretchability of the OTFT is also demonstrated by operating the transistor while adhered to a finger being flexed. The ability to pattern highly conductive Ag NW networks using laser ablation to pattern electrodes as well as interconnects provides a simple strategy to produce complex stretchable OTFT-based circuits.
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Plastic products are widely used in different applications. Thus, exposure of human and other organisms to these products may affect their biological system. The current study was conducted to investigate the potential deleterious effect of Polysterene nanoparticles (PS-NPs) on the liver and to state the cellular and molecular mechanisms associated with exposure to PS-NPs.30 male rats were divided randomly and equally into 3 groups; control (distilled water), low dose (3 mg/kg/day) and high dose (10 mg/kg/day) exposed group via oral gavage for 5 successive weeks. PS-NPs caused elevation in ALT, AST and MDA, upregulation of apoptosis-related genes and significant decrease in GSH and mRNA expression for antioxidant-related genes (Nrf-2 and GPx). Moreover, alterations in hepatic tissue architecture and positive caspase-3 expression was noticed in a dose- dependent manner. Collectively, PS-NPs can induce hepatoxicity in rats in a dose dependent manner, so the health risk of PS-NPs should not be ignored.
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Stretchable conductive polymer films are required to survive not only large tensile strain but also stay functional after the reduction in applied strain. In the deformation process, the elastomer substrate that is typically employed plays a critical role in the response of the polymer film. In this study, we examine the role of a PDMS elastomer substrate on the ability to achieve stretchable PDPP-4T films. Specifically, we consider the adhesion and near surface modulus of the PDMS tuned through UV/ozone treatment on the competition between film wrinkling and plastic deformation. We also consider the role of PDMS tension on the stability of films under cyclic strain. We find that increasing the near-surface modulus of the PDMS and maintaining the PDMS in tension throughout the cyclic strain process promotes plastic deformation over film wrinkling. In addition, the UV/ozone treatment increases film adhesion to the PDMS resulting in significantly reduced film folding and delamination. For 20 min UV/ozone treated PDMS, we show that a PDPP-4T film RMS roughness is consistently below 3 nm for up to 100 strain cycles with a strain range of 40 %. In addition, while the film is plastically deforming, the microstructural order is largely stable as probed with grazing incidence X-ray scattering and UV-visible spectroscopy. These results highlight the importance of the neighboring elastomer characteristics on the ability to achieve stretchable polymer semiconductors.
Article
Nanopolystyrene particles have been widely used in many fields. However, the molecular responses of organisms to nanopolystyrene particles at predicted environmentally relevant concentrations are still largely unclear. Caenorhabditis elegans is employed herein to investigate the molecular response of p38 mitogen‐activated protein kinase (MAPK) signaling to nanoplastic particles (1 µg L−1) and the underlying molecular mechanism. In wild‐type nematodes, prolonged exposure (from L1‐larvae to adult day 3) to nanopolystyrene particles increases the expression of pmk‐1 encoding a p38 MAPK. Mutation of pmk‐1 induces a susceptibility to nanopolystyrene toxicity, suggesting that the p38 MAPK signaling mediates a protective response to nanopolystyrene particles. PMK‐1 functions in the intestine to act upstream of two transcriptional factors (ATF‐7 and SKN‐1), which can further act upstream of XBP‐1, a key regulator of endoplasmic reticulum unfolded protein response (ER UPR), to regulate the response to nanopolystyrene particles. PMK‐1, ATF‐7, SKN‐1, and XBP‐1 are all required for the induction of intestinal ER UPR in nematodes exposed to nanopolystyrene particles. Therefore, the intestinal p38 MAPK signaling may mediate a protective response to nanopolystyrene particles by activating XBP‐1‐mediated ER UPR. The results herein highlight the importance of molecular response in the intestine of organisms to nanopolystyrene particles. The molecular responses of organisms to nanopolystyrene particles at predicted environmentally relevant concentrations are still largely unclear. In Caenorhabditis elegans, an intestinal p38 mitogen‐activated protein kinase signaling mediates a protective response to nanopolystyrene particles by activating XBP‐1‐mediated endoplasmic reticulum unfolded protein response. The results herein suggest the importance of intestinal response to nanopolystyrene particles in organisms.
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Abstract Substantial effort has been devoted to both scientific and technological developments of wearable, flexible, semitransparent, and sensing electronics (e.g., organic/perovskite photovoltaics, organic thin‐film transistors, and medical sensors) in the past decade. The key to realizing those functionalities is essentially the fabrication of conductive electrodes with desirable mechanical properties. Conductive polymers (CPs) of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have emerged to be the most promising flexible electrode materials over rigid metallic oxides and play a critical role in these unprecedented devices as transparent electrodes, hole transport layers, interconnectors, electroactive layers, or motion‐sensing conductors. Here, the current status of research on PEDOT:PSS is summarized including various approaches to boosting the electrical conductivity and mechanical compliance and stability, directly linked to the underlying mechanism of the performance enhancements. Along with the basic principles, the most cutting edge‐progresses in devices with PEDOT:PSS are highlighted. Meanwhile, the advantages and plausible problems of the CPs and as‐fabricated devices are pointed out. Finally, new perspectives are given for CP modifications and device fabrications. This work stresses the importance of developing CP films and reveals their critical role in the evolution of these next‐generation devices featuring wearable, deformable, printable, ultrathin, and see‐through characteristics.
Article
Electronic textiles (e-textiles) provide more comfort and aesthetic value than film-based portable devices that can be achieved with conventional silicon technology. To enhance feasibility at the industry level, it is highly desirable to develop reliable printed circuit textiles (PCTs) as a platform for commercially available circuit modules. This study demonstrates a means of fabricating PCTs with high freedom of circuit design, controllable pattern resolution and mechanical robustness under various hash environmental conditions. The process uses surface treatment of (3-aminopropyl)trimethoxysilane (APMTS) on cotton textile, a layer-by-layer (LBL) coating process with a conductive dye (PEDOT:PSS:Ag nanowires) and chitosan through conformal stencil layers, and an additional coating of a polytetrafluoroethylene (PTFE) protective layer. Under optimized conditions, the PCTs show a patterning ability on both sides of the textile with a low electrical resistance of 46 Ω lateral dimensions of 1.16 mm × 1.0 cm and reliable robustness under bending, stretching and 8585 tests. To demonstrate the feasibility of PCT, a joule heater and electrothermochromic display were successfully developed for e-textile applications.
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The conductive polymer complex poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) is the most explored conductive polymer for conductive textiles applications. Since PEDOT:PSS is readily available in water dispersion form, it is convenient for roll-to-roll processing which is compatible with the current textile processing applications. In this work, we have made a comprehensive review on the PEDOT:PSS-based conductive textiles, methods of application onto textiles and their applications. The conductivity of PEDOT:PSS can be enhanced by several orders of magnitude using processing agents. However, neat PEDOT:PSS lacks flexibility and strechability for wearable electronics applications. One way to improve the mechanical flexibility of conductive polymers is making a composite with commodity polymers such as polyurethane which have high flexibility and stretchability. The conductive polymer composites also increase attachment of the conductive polymer to the textile, thereby increasing durability to washing and mechanical actions. Pure PEDOT:PSS conductive fibers have been produced by solution spinning or electrospinning methods. Application of PEDOT:PSS can be carried out by polymerization of the monomer on the fabric, coating/dyeing and printing methods. PEDOT:PSS-based conductive textiles have been used for the development of sensors, actuators, antenna, interconnections, energy harvesting, and storage devices. In this review, the application methods of PEDOT:SS-based conductive polymers in/on to a textile substrate structure and their application thereof are discussed.
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The epigenetic regulation mechanisms for toxicity induction of nanoplastics in organisms remain largely unknown. In Caenorhabditis elegans, we found that prolonged exposure to 1-100 μg/L polystyrene nanoparticles (PS-NPs) decreased expression of MET-2, a H3K9 methyltransferase. Meanwhile, RNAi knockdown of met-2 suppressed the PS-NPs toxicity in inducing production of reactive oxygen species (ROS) and in decreasing locomotion behavior, which suggesting that the decrease in MET-2 expression reflected a protective response. This resistance to PS-NPs toxicity could be further detected in worms with met-2 RNAi knockdown in both intestinal cells and germline cells. In PS-NPs exposed worms, intestinal RNAi knockdown of met-2 significantly increased expressions of daf-16, bar-1, and elt-2. Intestinal RNAi knockdown of daf-16, bar-1, or elt-2 suppressed the resistance of met-2(RNAi) worms to PS-NPs toxicity, suggesting that MET-2 functioned upstream of ELT-2, BAR-1, and DAF-16 in intestinal cells to control PS-NPs toxicity. Moreover, in PS-NPs exposed worms, germline RNAi knockdown of met-2 significantly decreased expressions of wrt-3 and pat-12. RNAi knockdown of wrt-3 or pat-12 further inhibited the susceptibility of worms overexpressing germline MET-2 to PS-NPs toxicity, suggesting that MET-2 functioned upstream of PAT-12 and WRT-3 in germline cells to control PS-NPs toxicity. Therefore, our data provided an important molecular basis for MET-2-mediated methylation regulation in causing protective response to nanoplastics in organisms.
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Semitransparent organic photovoltaics (ST‐OPVs) provide a potentially facile route for some specific applications in building integrated photovoltaics. One of the challenges in developing the large‐scale printable ST‐OPVs is to address the need for a high‐performance and fully solution‐processed top electrode, allowing the replacement of the evaporated thin metallic films (Ag, Au, and Al). Silver nanowire (AgNW) is considered a promising candidate for the substitution due to its excellent transparency, conductivity and solution processability. Here, we report a novel bimodal AgNW electrode, comprising AgNWs of two different aspect ratios. It is shown that the bimodal AgNW (AgNW‐BM) film achieves lower sheet resistance and higher visible transmittance than each monodisperse AgNW film. Furthermore, ST‐OPVs based on PTB7‐Th:IEICO‐4F with AgNW‐BM top electrodes are fabricated, which can obtain a maximum power conversion efficiency (PCE) of 7.49% with an average visible transmittance (AVT) of 33%. The ST‐devices also demonstrate an enhanced reproducibility and excellent color‐rendering index of 90. In addition, the bimodal top electrode is successfully implemented in the PM6:Y6 system with a higher PCE of 9.79% with an AVT of 23%, demonstrating the universality for various semiconductor systems. Our work provides a simple strategy to realize the fully solution‐processed, highly efficient ST‐OPVs. This article is protected by copyright. All rights reserved.
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In Caenorhabditis elegans, long-term exposure to 20 nm polystyrene nanoparticles (PS-NPs) caused transgenerational toxicity. However, underlying mechanisms for induction of this transgenerational PS-NPs toxicity remain largely unknown. We here determined...
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Ion channels on cytoplasmic membrane function to sense various environmental stimuli. We here determined the changes of genes encoding ion channels in Caenorhabditis elegans after exposure to polystyrene nanoparticles (PS-NPs). Exposure to 1-1000 μg/L PS-NPs could increase expressions of egl-19, mec-10, trp-4, trp-2, tax-4, cca-1, unc-2, and unc-93, and decrease the expressions of cng-3, mec-6, ocr-2, deg-1, exc-4, kvs-1, and eat-2. Among these 15 ion channel genes, RNAi knockdown of cng-3 or eat-2 caused resistance to PS-NPs toxicity and RNAi knockdown of egl-19, cca-1, tax-4, or unc-93 induced susceptibility to PS-NPs toxicity, suggesting that cng-3, eat-2, egl-19, cca-1, tax-4, and unc-93 were involved in the control of PS-NPs toxicity. EGL-19 and CCA-1 functioned in intestinal cells to control PS-NPs toxicity, and CNG-3, EAT-2, EGL-19, TAX-4, and UNC-93 functioned in neuronal cells to control PS-NPs. Moreover, in intestinal cells of PS-NPs exposed worms, cca-1 RNAi knockdown decreased elt-2 expression, and egl-19 RNAi knockdown decreased daf-16 and elt-2 expressions. In neuronal cells of PS-NPs exposed worms, eat-2 RNAi knockdown increased jnk-1, mpk-1, and dbl-1 expressions, unc-93 RNAi knockdown decreased mpk-1 and daf-7 expressions, and tax-4 RNAi knockdown decreased jnk-1 and daf-7 expressions. Therefore, two molecular networks mediated by ion channels in intestinal cells and neuronal cells were dysregulated by PS-NPs exposure in C. elegans. Our data suggested that the dysregulation in expressions of these ion channels mediated a protective response to PS-NPs in the range of μg/L in worms.
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The deposition of certain amount of nanopolystyrene (NPS) could be observed in gonad of Caenorhabditis elegans. However, we still know little about the response of germline to NPS exposure. In the germline of C. elegans, NPS (1-1000 μg/L) increased expression levels of two G protein-coupled receptors (GPCRs), PAQR-2 and CED-1. Moreover, susceptibility to NPS toxicity was observed in ced-1(RNAi) worms, which suggested the protective response of germline mediated by GPCR CED-1. In the germline, five proteins (CED-10, VPS-34, SNX-1, RAB-7, and RAB-14) functioned as downstream targets of GPCR CED-1 in controlling NPS toxicity. Furthermore, these five targets in the germline regulated NPS toxicity by affecting the activities of p38 MAPK and insulin signaling pathways in intestinal cells. Therefore, we raised a GPCR CED-1-mediated signaling cascade in germline in response to NPS exposure, which is helpful for understanding the molecular basis of germline in response to NPS exposure.
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Opaque and semitransparent organic solar cells (OSCs) have made tremendous progress in recent years. Efficiencies over 18% and 13% have been demonstrated for opaque semitransparent OSCs, respectively. OSCs do not contain unfavorable elements such as lead, which makes it has broader potential applications when compared to other lead‐contained thin‐film solar cells. There has also been tremendous progress in the semitransparent OSCs (ST‐OSCs), which makes them extremely appealing for promising emerging applications such as building‐integrated photovoltaics. Herein, a progress review in the field is needed for helping the researchers better understand semitransparent OSCs and further realize their potentials. In this review, we summarized recent strategies in semitransparent OSCs based on three perspectives, including electrode engineering, active layer engineering, and device engineering. We also discuss the wide range of applications where ST‐OSCs can be used and point out challenges for future developments of ST‐OSCs. Finally, we present our outlook for promising future research directions. This article is protected by copyright. All rights reserved.
Article
Micro-transfer printing is an effective method that enables the integration of micro-scale heterogeneous materials for flexible electronics. As the key component of micro-transfer printing equipment, the stamp is adopted to pick up and print microdevices due to its reversible and controllable adhesion. In this paper, we propose a novel microstructured stamp based on the bionic theory, which consists of a microchamber and four microchannels. A theoretical model about the pressure change of the gas in the microchamber is established and the effects of compression distance and pull-up velocity on the pull-off force of the stamp are investigated. The performance test results show that the pull-off force of the stamp can be controlled by both the compression distance and the pull-up velocity. Finally, micro-transfer printing operations of microdevices with different sizes, shapes and materials are realized based on the proposed microstructured stamp. The results show that the proposed microstructured stamp exhibits good performance in the transfer printing of microdevices, and provides a new way for the design of microstructured stamps for micro-transfer printing without an extra excitation system.
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Dry adhesives that rely on surface force mediated adhesion, such as van der Waals forces, are important in applications ranging from robotics to manufacturing. The maximum theoretical adhesion strength of a contact is achieved when the stress is uniformly distributed over the entire contact area as the full potential of all the bonds at the interface is realized in this scenario. Most dry adhesive structures are composed of a tip layer that forms contact and a support structure that transfers load from the far field to this tip structure. Here, we determine the displacement distribution that must be applied on the tip layer to generate an optimum interfacial stress distribution. We realize this through a linear, closed-form optimization framework that uses data obtained from finite element analysis for a few basis cases. It was found that adhesion can be maximized by applying an optimum displacement on the tip layer that consists of uniform tension in the center, a peak tension between the center and the edge, and compression near the edge. The displacement applied on the tip layer of a mushroom-shaped, composite, and novel segmented composite structures are then analyzed and compared with the optimal case to guide the design of dry adhesives.
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Photodetectors that can sense not only light intensity but also light's polarization state add valuable information that is beneficial in a wide array of applications. Polymer semiconductors are an attractive material system to achieve intrinsic polarization sensitivity due to their anisotropic optoelectronic properties. In this report, the thermomechanical properties of the polymer semiconductors PBnDT‐FTAZ and P(NDI2OD‐T2) are leveraged to realize bulk heterojunction (BHJ) films with record in‐plane alignment. Two polymer blends with distinct weight average molar masses (Mw) are considered and either a strain‐ or rub‐alignment process is applied to align the polymer blend films. Optimized processing yields films with dichroic ratios (DR) of over 11 for the high Mw system and nearly 17 for the low Mw system. Incorporating the aligned films into photodetectors results in a polarized photocurrent ratio of 15.25 with corresponding anisotropy ratio of 0.88 at a wavelength of 530 nm, representing the highest reported photocurrent ratio for photodiodes that can operate in a self‐powered regime. The demonstrated performance showcases the ability of polymer semiconductors to achieve BHJ films with exceptional in‐plane polymer alignment, enabling high performance polarization sensitive photodetectors for incorporation into novel device architectures. Polymer semiconductor bulk heterojunction films are aligned using molecular weight dependent strategies to achieve highly oriented blend films. Integrating the films in organic photodetectors, a polarized photocurrent ratio of over 15 is demonstrated at a wavelength of 530 nm. The intrinsically polarization sensitive photodetector is utilized to effectively image a polarized scene.
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The perovskite solar cells (PSCs) and organic solar cells (OSCs) with high performance were fabricated with transfer-printed top metal electrodes. We have demonstrated that PSCs and OSCs with the top Au electrodes fabricated by using the transfer printing method have comparable or better performance than the devices with the top Au electrodes fabricated by using conventional thermal evaporation method. The highest PCE of the PSCs and OSCs with the top electrodes fabricated using the transfer printing method achieved 13.72% and 2.35%, respectively. It has been investigated that fewer defects between the organic thin films and Au electrodes exist by using the transfer printing method which improved the device stability. After stored the PSCs and OSCs with the transfer-printed electrodes in a nitrogen environment for 97 days and 103 days without encapsulation, the PSCs and OSCs still retained 71% and 91% of their original PCEs, respectively.
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Unlabelled: Highly conductive, flexible, and transparent electrodes (FTEs) of Pedot: PSS films on plastic substrates have been achieved using strong acid treatments. However, it is rare to realize a performance attenuation of Pedot: PSS FTEs on plastic substrates and flexible optoelectronic devices because of strong acid residues in the Pedot: PSS matrix. Herein, we develop a feasible transfer-printing technique using mild acids. Because of a mild and weak property of these acids and less acid residues in Pedot: PSS matrix, the transferred Pedot: PSS FTEs exhibited a significant enhancement in stability, conductivity (3500 S cm(-1)), transparency, and mechanical flexibility on plastic substrates. Flexible organic solar cells with the FTEs also showed a remarkable enhancement in power conversion efficiency and stability in the ambient atmosphere. It is expected that the novel transfer-printing technique for making Pedot: PSS FTEs is also useful in many other types of flexible optoelectronic devices.
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This paper describes the stretching and conformal bonding (i.e., decal-transfer printing) of organic solar cells in both the "conventional" and "inverted" configurations to hemispherical glass surfaces with radii of 8 mm. This action produces equivalent biaxial tensile strains of 24%, which many materials used, in organic electronic devices cannot accommodate without fracture. Consideration of the mechanical properties of conjugated polymers reveals a surprising effect of a single structural parameter the length of the alkyl side chain on the elasticity and ductility of regioregular polythiophene. This analysis enables selection of materials that can accommodate sufficient tensile strain for non-planar applications. For polymer-fullerene solar cells, devices based on the elastic and ductile poly(3-octylthiophene) (P30T) exhibit typical photovoltaic properties when bonded to hemispherical glass substrates, while those based on the relatively brittle poly(3-hexylthiophene) (P3HT) exhibit extensive cracking, which degrades the photovoltaic effect significantly. The results suggest that mechanical properties should be taken into account when designing and selecting organic semiconductors for applications that demand significant deformation.
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We report on semitransparent air-processed all-plastic solar cells, fabricated from vacuum-free processes, comprising two polymer electrodes, a polymeric work-function modification layer and a polymer:fullerene photoactive layer. The active layer and the top PEDOT:PSS electrode were prepared by sequential film-transfer lamination on polyethylenimine-modified PEDOT:PSS bottom electrodes. The transferring of films offers ease of layer patterning and the misalignment of defects in the different layers resulting from the additive film transfer lamination process yields high shunt resistance values of 108 ohm cm2. Consequently, all-plastic solar cells fabricated with this process exhibit very low reverse bias dark current and can operate in the photovoltaic quadrant with light irradiance varying over five orders of magnitude. The analysis of the values of the open-circuit voltage as a function of light irradiance over that wide dynamic range points toward an ideality factor of n = 1.82 and a reverse saturation current density of 6.2 × 10−11 A cm−2 for solar cells with an active layer comprised of a blend of poly(3-hexylthiophene) and an indene fullerene bis-adduct.
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An ultrathin, smooth, and low-loss Ag film without a wetting layer is achieved by co-depositing a small amount of Al into Ag. The film can be as thin as 6 nm, with a roughness below 1 nm and excellent mechanical flexibility. Organic photovoltaics that use these thin films as transparent electrode show superior efficiency to their indium tin oxide (ITO) counterparts because of improved photon management.
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In this study, we demonstrate linearly polarized organic photovoltaic cells with a well-controlled level of polarization sensitivity. The polarized devices were created through the application of a large uniaxial strain to the bulk heterojunction poly(3-hexylthiophene):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) film and printing the plastically deformed active layer onto a PEDOT:PSS and indium tin oxide coated glass substrate. The P3HT:PCBM layer is processed such that it is able to accommodate high strains (over 100%) without fracture. After printing the strained films, thermal annealing is used to optimize solar cell performance while maintaining polarization sensitivity. A dichroic ratio and short circuit current ratio of ≈6.1 and ≈1.6 were achieved, respectively.
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An external dielectric coating is shown to enhance energy conversion in an organic photovoltaic cell with metal anode and cathode by increasing the optical field intensity in the organic layers. Improved light incoupling in the device is modeled using transfer matrix simulations and is confirmed by in situ measurement of the photocurrent during growth of the coating. The optical field intensity in optimized cell geometries is predicted to exceed that in analogous devices using indium tin oxide, both cell types having equivalent anode sheet resistance, suggesting a broader range of compatible substrates (e.g., metal foils) and device processing techniques.
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We report on indium tin oxide (ITO)-free and metal-free semitransparent organic solar cells with a high-conductivity poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000) as both the bottom and the top electrodes. The PH1000 film showed a conductivity of 680±50 S/cm. A ZnO layer was used as an interlayer to produce an electron-selective electrode. The semitransparent devices with a structure of glass/PH1000/ZnO/poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester/PEDOT:PSS (CPP 105 D)/PH1000 exhibited an average power conversion efficiency of 1.8% estimated for 100 mW/cm2 air mass 1.5 global illumination. This geometry alleviates the need of vacuum deposition of a top electrode.
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An increasing number of technologies require large-scale integration of disparate classes of separately fabricated objects into spatially organized, functional systems1-9. Here we introduce an approach for heterogeneous integration based on kinetically controlled switching between adhesion and release of solid objects to and from an elastomeric stamp. We describe the physics of soft adhesion that govern this process and demonstrate the method by printing objects with a wide range of sizes and shapes, made of single-crystal silicon and GaN, mica, highly ordered pyrolytic graphite, silica and pollen, onto a variety of substrates without specially designed surface chemistries or separate adhesive layers. Printed p-n junctions and photodiodes fixed directly on highly curved surfaces illustrate some unique device-level capabilities of this approach.
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In recent years, the use of biopolymers as interface materials between inorganic electronics and biological tissues has increased, which has necessitated the integration of micro- and nanofabrication techniques with these unconventional materials. This combination has led to devices with intriguing operational characteristics such as so-called “transient” bioresorbable devices. Here, a method is investigated which leverages the thermal reflow characteristics of non-beta-sheet crystallized silk fibroin protein films to transfer print electronic components onto bioresorbable silk substrates. This is accomplished by applying heat and pressure to the interface of the silk and fabricated components, leading to reflow of the silk and transfer of the components from a silicon carrier wafer onto silk. We demonstrate application of this for both traditional (Au) and highly labile transient metals (Mg), over large areas with single micrometer resolution, all while retaining functionality of the transferred components. Additionally, it is shown how control over the reflow characteristics of silk through the process parameters can lead to both water-stable and water-soluble device outcomes and retain the efficacy of entrained biological dopants within the silk substrate matrix. Through these means, this method has the potential to improve the number of fabrication options for devices at the biotic/abiotic interface.
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Low dark current is critical to realize high-performance near infrared organic photodetectors (NIR OPDs). In general, organic photodetectors (OPDs) are with vacuum-deposited metals as the top electrode. The deposition of such metal would inevitably form doping to the organic active layer and thus yields high dark current. Here, we employ transfer-printing conducting polymer (tp-CP) as the top electrode instead of the vacuum-deposited metal electrode. The photodetector with the tp-CP electrode exhibits over two orders of magnitude lower dark current density than the device with the vacuum-deposited metal electrode. The photodetector with tp-CP electrode displays a responsivity of 0.37 A/W at 850 nm and a low dark current density of 3.0 nA/cm2 at -0.2 V based on a near-infrared (NIR) active layer of PMDPP3T:PC61BM that absorbs photons up to 1000 nm. The detectivity of the NIR photodetector reaches as high as over 10^13 Jones. Furthermore, the top PEDOT:PSS electrode is highly transparent, the NIR photodetector is double-side responsive to incident light, either from the bottom or the top electrode, since the top tp-CP electrode shows similar transparency as the bottom indium-tin oxide electrode.
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Specific morphological features of polymer semiconductors are often promoted in devices to optimize optoelectronic behavior. Less studied is the role of morphology on the mechanical properties of the film, such as elastic modulus, which is an important property for the development of flexible and stretchable devices. To gain insight into the morphological origin of elasticity in polymer semiconductors and its relationship to charge transport, we study the anisotropic in-plane elastic modulus of strain-aligned regioregular poly(3-hexylthiophene) (P3HT) films and compare the results to previously measured field effect charge mobility. The film morphology is varied through the amount of applied strain and post strain thermal annealing. Morphological characterization includes UV–vis optical spectroscopy and X-ray diffraction. The elastic modulus is measured using a buckling-based measurement technique. The elastic modulus of the film is found to decrease as the film is plastically strained. Thermally annealing the strained films results in a large in-plane elastic modulus anisotropy, where the modulus increases in the direction of backbone alignment and decreases in the transverse direction. The measured elastic modulus is compared to the film morphology, showing a dependence on both in-plane polymer chain alignment and local aggregate order. Comparing the elastic modulus to field effect mobility shows that they are not necessarily correlated, which has important implication for flexible organic electronic device design.
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Conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has attracted significant attention as a hole transport and electrode layer that substitutes metal electrodes in flexible organic devices. However, its weak cohesion critically limits the reliable integration of PEDOT:PSS in flexible electronics, which highlights the importance of further investigation of the cohesion of PEDOT:PSS. Furthermore, the electrical conductivity of PEDOT:PSS is insufficient for high current-carrying devices such as organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs). In this study, we improve the cohesion and electrical conductivity through adding dimethyl sulfoxide (DMSO), and we demonstrate the significant changes in the properties that are dependent on the wt.% of DMSO. In particular, with the addition of 3 wt.% DMSO, the maximum enhancements for cohesion and electrical conductivity are observed where the values increase by 470% and 6050%, respectively, due to the inter-PEDOT bridging mechanism. Furthermore, when OLED devices using the PEDOT:PSS films are fabricated using the 3 wt.% DMSO, the display exhibits 18% increased current efficiency.
Article
We report on the film preparation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by transfer lamination using plastic wrap as the transfer medium. Comparing with the commonly used polydimethylsiloxane (PDMS) transfer medium, the plastic wrap is cheaper, easier to access and for mass production. The surface of plastic wrap is less hydrophobic than that of PDMS, aqueous PEDOT: PSS solution with 0.5 wt.% surfactant can wet the plastic wrap well. No plasma or ultraviolet ozone treatment is needed on the plastic wrap prior to the coating of PEDOT: PSS, while plasma treatment is necessary when PDMS is used transfer medium. That simplifies the fabrication process. Organic solar cells with the PEDOT: PSS top electrode transferred using plastic wrap transfer medium exhibit an averaged fill factor of 0.60 and an averaged power conversion efficiency of 4.0%, comparable to that of reference solar cells with PDMS as transfer medium for PEDOT: PSS transfer.
Article
The role of molecular orientation of a polar conjugated polymer in polymer-fullerene organic photovoltaic (OPV) cells is investigated. A planar heterojunction (PHJ) OPV cell composed of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) is used as a model system to isolate the effect of the interfacial orientation on the photovoltaic properties. The molecular orientation of the aggregate P3HT relative to the PCBM layer is varied from highly edge-on (conjugated ring plane perpendicular to the interface plane) to appreciably face-on (ring plane parallel to the interface). It is found that as the P3HT stacking becomes more face-on there is a positive correlation to the OPV open circuit voltage (VOC), attributed to a shift in the highest occupied molecular orbital (HOMO) energy level of P3HT. In addition, the PHJ OPV cell with a broad P3HT stacking orientation distribution has a VOC comparable to an archetypal bulk heterojunction (BHJ) device. These results suggest that in the BHJ OPV cell, the hole energy level in the charge transfer state is defined in-part by the orientation distribution of the P3HT at the interface with PCBM. Finally, the photoresponse of the devices are also shown to have a dependence on P3HT stacking orientation.
Article
In this work, we report a nonionic surfactant (polyethylene glycol 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol ether, PEG-TmDD) that can improve the wetting property of PEDOT:PSS aqueous solution on the organic photoactive layer and simultaneously enhance the electrical conductivity of PEDOT:PSS film up to 526 S/cm. Furthermore, the conductivity enhancement is significantly dependent on the thermal annealing, which is contrary to the conductivity behavior of PEDOT:PSS film prepared from the formulation added with ethylene glycol (EG) where the conductivity is almost independent of the thermal annealing. The temperature dependence of the conductivity of PEDOT:PSS by PEG-TmDD is possibly ascribed to decomposition of PEG-TmDD into EG and TmDD during thermal annealing. With the high conductivity and good wetting on the active layer, PEDOT:PSS mixed with PEG-TmDD is used as the top electrode for organic solar cells. The cells exhibit a fill factor of 60% and a power conversion efficiency of 4.1% using poly(3-hexylthiophene):indene-C60 bis-adduct as the active layer. The results indicate that the new formulation of PEDOT:PSS mixed with PEG-TmDD is suitable for preparing a top electrode for vacuum-free organic solar cells.
Article
Unlabelled: We report perovskite solar cells with a new device structure that employ highly conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) ( Pedot: PSS) as the top electrode replacing commonly used metal electrodes. The Pedot: PSS top electrode is prepared from its aqueous solution through a transfer-lamination technique rather than direct spin-coating, which converts the CH(3)NH(3)PbI(3) into PbI(2). Perovskite solar cells with the structure of glass/FTO/c-TiO(2)/m-TiO(2)/CH(3)NH(3)PbI(3)/spiro-OMeTAD/PEDOT:PSS yield a maximum open-circuit voltage (V(OC)) of 1.02 V, and a maximum power conversion efficiency (PCE) of 11.29% under AM1.5 100 mW/cm(2) illumination. The whole device was fabricated in air without high-vacuum deposition which simplifies the processing and lowers the threshold of both scientific research and industrial production of perovskite solar cells.
Article
A novel transfer-printing method for high-performance all-plastic transparent electrodes is demonstrated. A solution process using H2 SO4 not only dramatically enhances the electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) over 4000 S cm(-1) but also chemically modifies its adhesion properties, thereby enabling expeditious "pick-and-place" transfer onto arbitrary surfaces using elastomeric stamps. Flexible and transparent optoelectronic devices with transferred PEDOT:PSS electrodes show superb performances. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Article
Despite the ubiquity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in applications demanding mechanical flexibility, the effect on the mechanical properties of common additives—i.e., dimethylsulfoxide (DMSO), Zonyl fluorosurfactant (Zonyl), and poly(ethyleneimine) (PEI)—has not been reported. This paper describes these effects and uses plasticized films in solar cells and mechanical sensors for the detection of human motion. The tensile moduli of films spin-coated from solutions containing 0%, 5%, and 10% DMSO and 0.1%, 1%, and 10% Zonyl (nine samples total) are measured using the buckling technique, and the ductility is inferred from measurements of the strain at which cracks form on elastic substrates. Elasticity and ductility are maximized in films deposited from solutions containing 5% DMSO and 10% Zonyl, but the conductivity is greatest for samples containing 0.1% Zonyl. These experiments reveal enlargement of presumably PEDOT-rich grains, visible by atomic force microscopy, when the amount of DMSO is increased from 0% to 5%. PEI—which is used to lower the work function of PEDOT:PSS—has a detrimental effect on the mechanical properties of the PEDOT:PSS/PEI bilayer films. Wearable electronic sensors employing PEDOT:PSS films containing 5% DMSO and 10% Zonyl are ­fabricated, which exhibit detectable responses at 20% strain and high mechanical robustness through elastic deformation.
Article
Here, we report significant improvements of Voc and FF in Sb2S3 quantum dot (QD)-based, solid-state heterojunction solar cells prepared from the solid transfer of preformed PEDOT:PSS hole extraction layers. Despite the moderate optical properties of Sb2S3 QDs, the solid state QD solar cells suffer from poor power conversion efficiency (PCE) resulting from the disappointing Voc and the high series resistance since there is inefficient charge extraction from QDs to the metal top electrode. In order to improve the hole extraction performance, a significantly uniform PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)) layer was transferred on the hole transport layer (P3HT, poly(3-hexylthiophene-2,5-diyl)) by using a simple solid-transfer method. In contrast with conventional spin-cast methods, the hydrophilic PEDOT:PSS layer was uniformly coated on the hydrophobic P3HT layer without any significant detriment to P3HT film properties. Due to improved contact surface for the Au top electrode and hole conductance resulting in significantly improved charge extraction, the power conversion efficiency was dramatically enhanced. Furthermore, the thickness of the PEDOT:PSS film was precisely optimized by layer-by-layer solid transfer, and thereby the PCE of the PEDOT:PSS solid-transfer device (30 nm) was improved by 25.7% in comparison to the PEDOT:PSS spin-cast device and by 76% in comparison to the PEDOT:PSS free device.
Article
The goal of this study is to determine the electrically conductivity of the polymers poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate): N-methyl-2-pyrrolidinone (PEDOT: PSS: NMP) and PEDOT: PSS when blended with polyvinyl alcohol (PVA). While the conducting polymers have high conductivity when not blended with PVA, they are brittle and difficult to spin-coat. Thus, the motivation for this study is to develop blends of these two conducting polymers with PVA to produce a material with optimized mechanical properties and that can also be spin-coated. The blends are produced using aqueous preparations of these materials. Mixtures of various weight percentages (wt %) of PEDOT: PSS: NMP and PEDOT: PSS are prepared and spin-coated on glass slides to form thin films. In the blends, the film conductivity increases with increasing content of either PEDOT: PSS: NMP or PEDOT: PSS. For example, 100 wt % of PEDOT: PSS: NMP and 60 wt % of PEDOT: PSS: NMP blended with PVA exhibit conductivities of, respectively, 10 and 4.02 S/cm. In contrast, conductivities of only 0.0525 and 0.000506 S/cm are observed, respectively, for 100 wt % of PEDOT: PSS and 60 wt % of PEDOT: PSS content in the PEDOT: PSS/PVA blends (No NMP). The addition of the NMP enhances the electrical conductivity by two to five orders of magnitude (depending on the amount of PVA in the blend) due to conformational change of PEDOT chains. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Article
Organic photovoltaics devices typically utilize illumination through a transparent substrate, such as glass or an optically clear plastic. Utilization of opaque substrates, including low cost foils, papers, and textiles, requires architectures that instead allow illumination through the top of the device. Here, we demonstrate top-illuminated organic photovoltaics, employing a dry vapor-printed poly(3,4-ethylenedioxythiophene) (PEDOT) polymer anode deposited by oxidative chemical vapor deposition (oCVD) on top of a small-molecule organic heterojunction based on vacuum-evaporated tetraphenyldibenzoperiflanthene (DBP) and C60 heterojunctions. Application of a molybdenum trioxide (MoO3) buffer layer prior to oCVD deposition increases the device photocurrent nearly 10 times by preventing oxidation of the underlying photoactive DBP electron donor layer during the oCVD PEDOT deposition, and resulting in power conversion efficiencies of up to 2.8% for the top-illuminated, ITO-free devices, approximately 75% that of the conventional cell architecture with indium-tin oxide (ITO) transparent anode (3.7%). Finally, we demonstrate the broad applicability of this architecture by fabricating devices on a variety of opaque surfaces, including common paper products with over 2.0% power conversion efficiency, the highest to date on such fiber-based substrates.
Article
Despite the ubiquity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a transparent conducting electrode in flexible organic electronic devices, its potential as a stretchable conductor has not been fully explored. This paper describes the electronic and morphological characteristics of PEDOT:PSS on stretchable poly(dimethylsiloxane) (PDMS) substrates. The evolution of resistance with strain depends dramatically on the methods used to coat the hydrophobic surface of PDMS with PEDOT:PSS, which is cast from an aqueous suspension. Treatment of the PDMS with an oxygen plasma produces a brittle skin that causes the PEDOT:PSS film to fracture and an increase in resistivity by four orders of magnitude at only 10% strain. In contrast, a mild treatment of the PDMS surface with ultraviolet/ozone (UV/O3) and the addition of 1% Zonyl fluorosurfactant to the PEDOT:PSS solution produces a mechanically resilient film whose resistance increases by a factor of only two at 50% strain and retains significant conductivity up to 188% strain. Examination of the strained surfaces of these resilient PEDOT:PSS films suggests alignment of the grains in the direction of strain. Wave-like buckles that form after the first stretch >10% render the film reversibly stretchable. Significant cracking (2 cracks mm–1) occurs at 30% uniaxial strain, beyond which the films are not reversibly stretchable. Cyclic loading (up to 1000 stretches) produces an increase in resistivity whose net increase in resistance increases with the value of the peak strain. As an application, these stretchable, conductive films are used as electrodes in transparent, capacitive pressure sensors for mechanically compliant optoelectronic devices.
Article
Microtransfer printing is a versatile process for retrieving, transferring, and placing nanomembranes of various materials on a diverse set of substrates. The process relies on the ability to preferentially propagate a crack along specific interfaces at different stages in the process. Here, we report a mechanics-based model that examines the factors that determine which interface a crack will propagate along in microtransfer printing with a soft elastomer stamp. The model is described and validated through comparison to experimental measurements. The effects of various factors, including interface toughness, stamp geometry, flaw sizes at the interfaces, and nanomembrane thickness, on the effectiveness of transfer printing are investigated using a fracture-mechanics framework and finite element modeling. The modeling results agree with experimental measurements in which the effects of interface toughness and nanomembranes thickness on the transfer printing yield were examined. The models presented can be used to guide the design of transfer printing processes.
Article
Solution processed polymer:fullerene solar cells on opaque substrates have been fabricated in conventional and inverted device confi gurations. Opaque substrates, such as insulated steel and metal covered glass, require a transparent conducting top electrode. We demonstrate that a high conducting (900 S cm − 1 ) PEDOT:PSS layer, deposited by a stamp-transfer lamination technique using a PDMS stamp, in combination with an Ag grid electrode provides a profi cient and versatile transparent top contact. Lamination of large size PEDOT:PSS fi lms has been achieved on variety of surfaces resulting in ITO-free solar cells. Power conversion effi ciencies of 2.1% and 3.1% have been achieved for P3HT:PCBM layers in inverted and conventional polarity confi gurations, respectively. The power conversion effi ciency is similar to conventional glass/ITO-based solar cells. The high fill factor (65%) and the unaffected open-circuit voltage that are consistently obtained in thick active layer inverted geometry devices, demonstrate that the laminated PEDOT:PSS top electrodes provide no signifi cant potential or resistive losses.
Article
We report that the π-stacking direction in poly(3-hexylthiophene) (P3HT) films can be made to orient strongly out-of plane by uniaxially straining films in orthogonal directions, providing a valuable opportunity to evaluate charge transport in a very unusual microstructure for this material. The structure of the films was characterized using UV–visible spectroscopy, X-ray diffraction, and near-edge X-ray absorption fine structure spectroscopy, showing that unstrained films have a weakly edge-on stacking character with a large orientation distribution, whereas films strained biaxially by 100% in orthogonal directions have highly face-on stacking. In the biaxially strained films the face-on packing occurs while the P3HT long axis orientation is found to be only weakly anisotropic in-plane. Charge transport is characterized in an organic thin-film transistor (OTFT) configuration, showing that the saturated field effect mobility in the biaxially strained films is greater than that for unstrained films for channel lengths ≤10 μm. The mobilities are found to have different channel-length dependence, attributed primarily to differences in the field-dependent charge-transport behavior, resulting in the mobility being comparable for channel lengths of 20 μm. The results suggest that edge-on packing is not a prerequisite for relatively high-field-effect mobility in P3HT-based OTFTs.
Article
Poly(3-hexylthiophene) (P3HT) is p-doped by the new soluble dopant molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene] and investigated via photoemission spectroscopy and transport measurements. Soft-contact transfer lamination of thin layers of the doped P3HT on undoped polymer layers is used to create spatially-confined doped regions, which serve as hole-injection contacts on P3HT diodes. This strategy is then used to create efficient hole-collecting contacts on solution-processed inverted polymer solar cells.
Article
The technologically important inkjet printed poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) films, at different extents of co-doping with dimethyl sulfoxide DMSO, have been studied in terms of in-plane charge transport and electric field force microscopy (EFM). Similarly to past studies of spin coated PEDOT:PSS films, room temperature conductivity is enhanced by a factor of 103 to 130 S cm−1 on the addition of 5% DMSO, Hall probe analysis demonstrated a decrease in contact resistance from 106 Ω to 104 Ω whilst variable-temperature conductivity analysis shows an increase in the VRH exponent from 0.25 to 0.5 signifying a charge transport evolution from Mott Variable Range Hopping in 3-dimensions to a pseudo 1-dimensional Variable Range Hopping. In addition, electric field force microscopy (EFM) showed a corresponding threefold increase in PEDOT grain size. Further analysis was conducted to determine the hopping length and the ratio of the hopping length versus localization length in the electron transport model.
Article
The mixing behavior of the hole- and electron-transporting materials in bulk heterojunction (BHJ) organic photovoltaic (OPV) blends plays a key role in determining the nanoscale morphology, which is believed to be a decisive factor in determining device performance. We present a systematic investigation of the mixing behavior between poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in model multilayer structures. The bilayer structures are composed of amorphous PCBM that is mechanically laminated to different P3HT layers with varying degrees of crystallinity. We find that mixing is significantly decreased as the crystallinity of P3HT is increased. The mixing behavior can be explained as resulting from (1) nearly complete miscibility of PCBM with amorphous P3HT (based on our results from regiorandom P3HT) and (2) the existence of tie chains between crystalline P3HT domains that restrain the swelling of the P3HT layer by PCBM. We also introduce a unique PCBM–P3HT–PCBM trilayer structure where one of the PCBM layers is highly crystalline. The crystalline PCBM dramatically alters the mixing behavior. Initial mixing of the amorphous PCBM into P3HT is followed by rapid cold crystallization at the crystalline PCBM layer, which depletes the PCBM in the P3HT layer. These bilayer and trilayer experiments illustrate that mixing of P3HT and PCBM is influenced by multiple factors, such as the semicrystalline nature of P3HT (overall crystallinity, characteristics of amorphous chains) and phase (amorphous or crystalline) of the PCBM.
Article
The nanometer-size crystallization of poly(3,4-ethylenedioxythiophene) (PEDOT) inside the hydrophobic core region of PEDOT:PSS (PSS: poly(4-styrenesulfonate)) in a solid film is found by small and wide-angle X-ray scatterings using a synchrotron radiation source. The clarified PEDOT:PSS structure indicates that a nanocrystal of PEDOT surrounded by PSS is grown in the solid film from randomly oriented PEDOT in a micelle dispersed in water during the course of film fabrication. The addition of ethylene glycol (EG) to the PEDOT:PSS water dispersion and post-treatment of the pristine film with EG both provide similar improvements in PEDOT crystallinity. The crystallite size of PEDOT increases up to a comparable size (4.8 nm) to the hydrophobic PEDOT core region of the micelle. The electrical conductivity of the solid film is concurrently enhanced by 2 orders of magnitude with the growing nanocrystal of PEDOT. These findings clearly demonstrate the importance of the single crystalline PEDOT assisted by EG to obtain high electrical conductivity of the PEDOT:PSS solid film.
Article
The DC conductivity (σDC) of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS) with various organic solvents was measured. The solvents used were dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF), tetrahydrofuran (THF), and H2O (as pristine solvent). Room temperature DC conductivity [σDC(RT)] of a free standing film of PEDOT/PSS with H2O was measured to be ∼0.8 S/cm. Through a change of solvents used, σDC(RT) of the samples increases from ∼0.8 to ∼80 S/cm. The temperature dependence of DC conductivity [σDC(T)] of PEDOT/PSS with H2O followed a quasi one-dimensional variable range hopping model, while that of PEDOT/PSS prepared from DMSO, DMF, and THF followed a power law (σDC ∝ Tβ). From X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) experiments, the doping concentration of the systems with different solvents was approximately the same. We analyzed that the screening effect of the solvent plays an important role for the variation of σDC of the PEDOT/PSS systems.
Article
A novel method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge-mobility anisotropy, where the in-plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two-dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane-on and edge-on packing configurations, as the strain alignment is found to induce a significant face-on orientation of the originally highly edge-on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge-mobility anisotropy of 9, providing a simple and effective method to investigate charge-transport mechanisms in polymer semiconductors.
Article
The morphology of the active layer in an organic photovoltaic bulk-heterojunction device is controlled by the extent and nature of phase separation during processing. We have studied the effects of fullerene crystallinity during heat treatment in model structures consisting of a layer of poly(3-hexylthiophene) (P3HT) sandwiched between two layers of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Utilizing a combination of focused ion-beam milling and energy-filtered transmission electron microscopy, we monitored the local changes in phase distribution as a function of annealing time at 140 oC. In both cases, dissolution of PCBM within the surrounding P3HT was directly visualized and quantitatively described. In the absence of crystalline PCBM, the overall phase distribution remained stable after intermediate annealing times up to 60 s; whereas microscale PCBM aggregates were observed after annealing for 300 s. Aggregate growth proceeded vertically from the substrate interface via uptake of PCBM from the surrounding region, resulting in a large PCBM-depleted region in their vicinity. When pre-crystallized PCBM was present, amorphous PCBM was observed to segregate from the intermediate P3HT layer and ripen the crystalline PCBM underneath, owing to the far lower solubility of crystalline PCBM within P3HT. This process occurred rapidly, with segregation already evident after annealing for 10 s and with uptake of nearly all of the amorphous PCBM by the crystalline layer after 60 s. No microscale aggregates were observed in the pre-crystallized system, even after annealing for 300 s.
Article
We report on an efficient solution-processable, top-absorbing organic photodetector with a polymer top electrode. The layer sequence is inverted, starting with the cathode as bottom electrode instead of an indium-tin-oxide (ITO) anode used in state-of-the-art organic detectors. The device comprises a bulk heterojunction of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as photoactive layer and a double layer of different formulations of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The lower PEDOT:PSS layer reduces the thermally generated dark current and the upper layer acts as anode. To increase the conductivity of the highly transparent (>90% at 500nm wave length) PEDOT:PSS electrode ethylene glycol is added. The influence of the anode sheet resistance Rsheet on important photodiode characteristics is investigated. For Rsheet=100Ω/sq high external quantum efficiency (>70% at 500nm) and high cut-off frequencies (>400kHz) can be reached. The performance of these inverted organic photodetectors is shown to be equal to state-of-the-art non-inverted detectors containing an ITO anode.
Article
We describe a transfer printing technique for directly patterning thin gold films onto GaAs surfaces. This additive transfer process is mediated by the presence of an alkane dithiol monolayer on the wafer surface. The transferred patterns are chemically bound to the wafer surface and they exhibit strong adhesion (i.e., they easily pass Scotch tape adhesion tests.) A variety of gold patterns with a wide range of feature sizes can be printed onto GaAs (100), (110), (211)A, and (211)B using this approach. © 2002 American Vacuum Society.
Article
The conductivity of a poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) film can be enhanced by more than two orders of magnitude by adding a compound with two or more polar groups, such as ethylene glycol, meso-erythritol (1.,2,3,4-tetrahydroxybutane), or 2-nitroenthanol, to an aqueous solution of PEDOT:PSS. The mechanism for this conductivity enhancement is studied, and a new mechanism proposed. Raman spectroscopy indicates an effect of the liquid additive on the chemical structure of the PEDOT chains, which suggests a conformational change of PEDOT chains in the film. Both coil and linear conformations or an expanded-coil conformation of the PEDOT chains may be present in the untreated PEDOT:PSS film, and the linear or expanded-coil conformations may become dominant in the treated PEDOT:sPSS film. This conformational change results in the enhancement of charge-carrier mobility in the film and leads to an enhanced conductivity. The high-conductivity PEDOT:PSS film is ideal as an electrode for polymer optoelectronic devices. Polymer light-emitting diodes and photovoltaic cells fabricated using such high-conductivity PEDOT:PSS films as the anode exhibit a high performance, close to that obtained using indium tin oxide as the anode.
Article
Highly conductive microfibers made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) were fabricated by wet-spinning and subsequent dip-treatment in ethylene glycol. The electrical conductivity of the PEDOT/PSS microfibers with a diameter of ca. 5μm was significantly increased from 74Scm−1 to 467Scm−1 by the dip-treatment in 3min. The result was explained by removal of insulating PSS from the surface of the PEDOT/PSS grains and crystallization of PEDOT, which led to the formation of large numbers of higher conductive grains that enhanced the transport of charge carriers in the microfiber. The mechanical properties of the microfibers were also improved by the dip-treatment where Young’s modulus and tensile strength increased from 3.2GPa and 94MPa to 4.0GPa and 130MPa, respectively.
Article
We describe a method for contact printing metal patterns with nanometer features over large areas. This nanotransfer printing (nTP) technique relies on tailored surface chemistries to transfer metal films from the raised regions of a stamp to a substrate when these two elements are brought into intimate physical contact. The printing is purely additive, fast (<15 s contact time), and it occurs in a single processing step at ambient conditions. Features of varying dimensions, including sizes down to ∼ 100 nm, can be printed with edge resolution better than 15 nm. Electrical contacts and interconnects for high-performance organic transistors and complementary inverter circuits have been successfully fabricated using nTP. © 2002 American Institute of Physics.
Article
Transfer printing is an important technique for assembling micro/nanomaterials on unusual substrates, with promising applications in the fabrication of stretchable and flexible electronics designed for use in areas such as biomedicine. The process involves retrieval of structures (e.g., micro-devices) from their growth (donor) substrate via an elastomeric stamp (i.e.. an element with posts on its surface), and then delivers them onto a different (receiver) substrate. An analytical mechanics model is developed to identify the key parameters for a shear-enhanced mode for transfer printing. The results predict that the pull-off force decreases linearly with increasing shear strain in the post, or with shear displacement across the stamp. This prediction agrees well with the experiments. Published by Elsevier Ltd.
Article
We demonstrate a method that uses the pillars on a stamp to cut and exfoliate graphene islands from a graphite and then uses transfer printing to place the islands from the stamp into the device active-areas on a substrate with a placement accuracy potentially in nanometers. The process can be repeated to cover all device active-areas over an entire wafer. We also report the transistors fabricated from the printed graphene. The transistors show a hole and electron mobility of 3735 and 795 cm2/V-s, respectively, and a maximum drive-current of 1.7 mA/μm (at VDS = 1 V), which are among the highest reported for room temperature. The effects of various transferring and fixing layers on sticking graphenes to a stamp and to a substrate, respectively, were also investigated.
Article
We introduce a novel approach, nanotransfer printing (nTP), to fabricate top-contact electrodes in Au/1,8-octanedithiol/GaAs junctions. Current−voltage and photoresponse experiments were conducted to evaluate the nature of electrical contact. Results show that the nTP method produces superior devices in which the electrical transport in nTP devices occurs through the 1,8-octanedithiol molecules. By contrast, conventional evaporation of Au onto the molecules results in direct Au/GaAs contacts. Thus, nTP is potentially useful for making electrical contacts in molecular electronics.
Article
An energy balance shows that the force required to peel an elastic film from a rigid substrate depends not only on the adhesive surface energy but also on an elastic deformation term. This elastic term, tending to reduce the adhesion force, can only be significant in two instances: for materials which can support stresses approaching the elastic modulus without fracturing, and for very small peel angles. Experiments using rubber peeling from glass over a range of peel angles support the theory.
Article
We have demonstrated a top-illuminated organic photovoltaic device with a thick Ag anode and a thin Ag cathode capped with an α-naphthylphenylbiphenyl diamine (NPB) thin film. The surface of the Ag anode was oxidized by UV–ozone which improved the carrier collection and reduced the exciton quenching. Compared with the control device with an indium tin oxide anode, a 15.59 times reduction in the serial resistance and a 1.72 times increase in the shunt resistance were observed with a fill factor of 0.61 in such a device. The NPB capping layer not only improved the light transmission from the semitransparent cathode, but also hindered the formation of Ag island growth and thereby improved the device stability.
Article
a Centro ricerche per le energie non convenzionali, Istituto ENI Donegani, ENI S.p.A., via G. Fauser 4, a b s t r a c t The growing interest in organic photovoltaics and the potential for a future mass production urges to find alternatives to the presently employed materials that are well performing but not convenient from the point of view of large area fabrication. Electrodes based on non abundant elements, or that constitute an issue for devices (i) long term stability, (ii) mechanical robustness and (iii) continuous fabrication process, shall be possibly soon replaced by earth abundant, easy processable and sustainable materials. Many groups have recently started to devote their research work on materials not containing metals or metal oxides, and the time has come to summarise the progress that has been reached so far.
Article
Transfer printing represents a set of techniques for deterministic assembly of micro-and nanomaterials into spatially organized, functional arrangements with two and three-dimensional layouts. Such processes provide versatile routes not only to test structures and vehicles for scientific studies but also to high-performance, heterogeneously integrated functional systems, including those in flexible electronics, three-dimensional and/or curvilinear optoelectronics, and bio-integrated sensing and therapeutic devices. This article summarizes recent advances in a variety of transfer printing techniques, ranging from the mechanics and materials aspects that govern their operation to engineering features of their use in systems with varying levels of complexity. A concluding section presents perspectives on opportunities for basic and applied research, and on emerging use of these methods in high throughput, industrial-scale manufacturing.
Article
The fabrication of functional multilayered conjugated-polymer structures with well-defined organic-organic interfaces for optoelectronic-device applications is constrained by the common solubility of many polymers in most organic solvents. Here, we report a simple, low-cost, large-area transfer-printing technique for the deposition and patterning of conjugated-polymer thin films. This method utilises a planar poly(dimethylsiloxane) (PDMS) stamp, along with a water-soluble sacrificial layer, to pick up an organic thin film (∼20 nm to 1 µm) from a substrate and subsequently deliver this film to a target substrate. We demonstrate the versatility of this transfer-printing technique and its applicability to optoelectronic devices by fabricating bilayer structures of poly(9,9-di-n-octylfluorene-alt-(1,4-phenylene-((4-sec-butylphenyl)imino)-1,4-phenylene))/poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (TFB/F8BT) and poly(3-hexylthiophene)/methanofullerene([6,6]-phenyl C61 butyric acid methyl ester) (P3HT/PCBM), and incorporating them into light-emitting diodes (LEDs) and photovoltaic (PV) cells, respectively. For both types of device, bilayer devices fabricated with this transfer-printing technique show equal, if not superior, performance to either blend devices or bilayer devices fabricated by other techniques. This indicates well-controlled organic-organic interfaces achieved by the transfer-printing technique. Furthermore, this transfer-printing technique allows us to study the nature of the excited states and the transport of charge carriers across well-defined organic interfaces, which are of great importance to organic electronics.