Mass production of a 3D non-woven nanofabric with crystalline P3HT nanofibrils for organic solar cells
20 Feb 2013-Energy and Environmental Science (The Royal Society of Chemistry)-Vol. 6, Iss: 3, pp 910-917
TL;DR: In this article, a strategy for the in line mass production of a 3D non-woven nanofabric consisting of crystalline P3HT nanofibrils, created by in situ cooling of the transportation line to feed a P3H solution for a coating tool, was introduced.
Abstract: A strategy for the in line mass production of a three-dimensional (3D) non-woven nanofabric consisting of crystalline P3HT nanofibrils, created by in situ cooling of the transportation line to feed a P3HT solution for a coating tool, was introduced. The required cooling-temperature with respect to the feeding rate for the overall nanofibril creating process and the yield of the nanofibrils in solution with various organic solvents were determined. Considering the influence of a change in the temperature on the status of the precipitated nanofibrils until feeding it into the spray nozzle, the margin of the surviving nanofibrils at a certain temperature was also investigated. To verify the superiority of our strategy and present directions regarding its application to industry, arrays of organic solar cells based on a 3D non-woven nanofabric structure consisting of P3HT nanofibrils were designed and fabricated using our in situ process combined with a spray-coating system. As a result, through the in situ cooling process, a considerable solar energy harvesting efficiency near 4%, which is a state-of-the-art value in a bi-layer-based solar cell, was obtained.
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TL;DR: Organic solar cells with a photonic crystal nanostructure embossed in the photoactive bulk heterojunction layer are reported, a topography that exhibits a 3-fold enhancement of the absorption in specific regions of the solar spectrum in part through multiple excitation resonances.
Abstract: We report organic solar cells with a photonic crystal nanostructure embossed in the photoactive bulk heterojunction layer, a topography that exhibits a 3-fold enhancement of the absorption in specific regions of the solar spectrum in part through multiple excitation resonances. The photonic crystal geometry is fabricated using a materials-agnostic process called PRINT wherein highly ordered arrays of nanoscale features are readily made in a single processing step over wide areas (approximately 4 cm(2)) that is scalable. We show efficiency improvements of approximately 70% that result not only from greater absorption, but also from electrical enhancements. The methodology is generally applicable to organic solar cells and the experimental findings reported in our manuscript corroborate theoretical expectations.
218 citations
TL;DR: This study suggests a simple way to simultaneously address all of these issues through the addition of a small amount of a nonionic surfactant (Triton X-100) to commercial PEDOT:PSS solutions.
Abstract: The use of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in electrodes and electrical circuits presents a number of challenges that are yet to be overcome, foremost amongst which are its relatively low conductivity, low coatability on hydrophobic substrates, and decreased conductivity at large strains. With this in mind, this study suggests a simple way to simultaneously address all of these issues through the addition of a small amount of a nonionic surfactant (Triton X-100) to commercial PEDOT:PSS solutions. This surfactant is shown to considerably reduce the surface tension of the PEDOT:PSS solution, thus permitting conformal coatings of PEDOT:PSS thin film on a diverse range of hydrophobic substrates. Furthermore, this surfactant induces the formation of PEDOT nanofibrils during coating, which led to the high conductivity values and mechanical stability at large strains (e=10.3%). Taking advantage of the superior characteristics of these PEDOT:PSS thin films, a highly flexible polymer solar cell was fabricated. The power conversion efficiency of this solar cell (3.14% at zero strain) was preserved at large strains (e=7.0%).
135 citations
TL;DR: In this paper, the composition and thickness-matching of SqP active layers has been compared with traditional blend casting (BC) and sequential processing (SqP), where the pure polymer and fullerene materials are cast sequentially from different solutions.
Abstract: Polymer:fullerene bulk heterojunction (BHJ) solar cell active layers can be created by traditional blend casting (BC), where the components are mixed together in solution before deposition, or by sequential processing (SqP), where the pure polymer and fullerene materials are cast sequentially from different solutions. Presently, however, the relative merits of SqP as compared to BC are not fully understood because there has yet to be an equivalent (composition- and thickness-matched layer) comparison between the two processing techniques. The main reason why matched SqP and BC devices have not been compared is because the composition of SqP active layers has not been accurately known. In this paper, we present a novel technique for accurately measuring the polymer:fullerene film composition in SqP active layers, which allows us to make the first comparisons between rigorously composition- and thickness-matched BHJ organic solar cells made by SqP and traditional BC. We discover that, in optimal photovoltaic devices, SqP active layers have a very similar composition as their optimized BC counterparts (≈44-50 mass % PCBM). We then present a thorough investigation of the morphological and device properties of thickness- and composition-matched P3HT:PCBM SqP and BC active layers in order to better understand the advantages and drawbacks of both processing approaches. For our matched devices, we find that small-area SqP cells perform better than BC cells due to both superior film quality and enhanced optical absorption from more crystalline P3HT. The enhanced film quality of SqP active layers also results in higher performance and significantly better reproducibility in larger-area devices, indicating that SqP is more amenable to scaling than the traditional BC approach. X-ray diffraction, UV-vis absorption, and energy-filtered transmission electron tomography collectively show that annealed SqP active layers have a finer-scale blend morphology and more crystalline polymer and fullerene domains when compared to equivalently processed BC active layers. Charge extraction by linearly increasing voltage (CELIV) measurements, combined with X-ray photoelectron spectroscopy, also show that the top (nonsubstrate) interface for SqP films is slightly richer in PCBM compared to matched BC active layers. Despite these clear differences in bulk and vertical morphology, transient photovoltage, transient photocurrent, and subgap external quantum efficiency measurements all indicate that the interfacial electronic processes occurring at P3HT:PCBM heterojunctions are essentially identical in matched-annealed SqP and BC active layers, suggesting that device physics are surprisingly robust with respect to the details of the BHJ morphology. © 2014 American Chemical Society.
52 citations
TL;DR: Investigating the photo-oxidation behavior of a bulk-heterojunction (BHJ) photoactive film made of single-crystalline poly(3-hexlythiophene) (P3HT) nanofibrils and fullerene derivatives showed significantly enhanced air stability under sunlight, whereas the PCE of the conventional BHJ solar cell decreased to 20% of its initial PCE under the same experimental conditions.
Abstract: In spite of the rapid increase in the power conversion efficiency (PCE) of polymer solar cells (PSCs), the poor stability of the photoactive layer in air under sunlight is a critical problem blocking commercialization of PSCs. This study investigates the photo-oxidation behavior of a bulk-heterojunction (BHJ) photoactive film made of single-crystalline poly(3-hexlythiophene) (P3HT) nanofibrils and fullerene derivatives [phenyl-C61-butyric methyl ester (PCBM), indene-C 60 bisadduct (ICBA)]. Because the single-crystalline P3HT nanofibrils had tightly packed π–π stacking, the permeation of oxygen and water into the nanofibrils was significantly reduced. Chemical changes in P3HT were not apparent in the nanofibrils, and hence the air stability of the nanofibril-based BHJ film was considerably enhanced as compared with conventional BHJ films. The chemical changes were monitored by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and UV–vis absorbance. Inverted PSCs made of the nanofibril-ba...
33 citations
TL;DR: The photoactive nanoweb substrates developed in this study may serve as platforms for producing stem cell therapeutics with enhanced neurogenesis and neuromodulation via optoelectrical control of stem cells.
Abstract: Optoelectrical manipulation has recently gained attention for cellular engineering; however, few material platforms can be used to efficiently regulate stem cell behaviors via optoelectrical stimulation. In this study, we developed nanoweb substrates composed of photoactive polymer poly(3-hexylthiophene) (P3HT) to enhance the neurogenesis of human fetal neural stem cells (hfNSCs) through photo-induced electrical stimulation. Methods The photoactive nanoweb substrates were fabricated by self-assembled one-dimensional (1D) P3HT nanostructures (nanofibrils and nanorods). The hfNSCs cultured on the P3HT nanoweb substrates were optically stimulated with a green light (539 nm) and then differentiation of hfNSCs on the substrates with light stimulation was examined. The utility of the nanoweb substrates for optogenetic application was tested with photo-responsive hfNSCs engineered by polymer nanoparticle-mediated transfection of an engineered chimeric opsin variant (C1V1)-encoding gene. Results The nanoweb substrates provided not only topographical stimulation for activating focal adhesion signaling of hfNSCs, but also generated optoelectrical stimulation via photochemical and charge-transfer reactions upon exposure to 539 nm wavelength light, leading to significantly enhanced neuronal differentiation of hfNSCs. The optoelectrically stimulated hfNSCs exhibited mature neuronal phenotypes with highly extended neurite formation and functional neuron-like electrophysiological features of sodium currents and action potentials. Optoelectrical stimulation with 539 nm light simultaneously activated both C1V1-modified hfNSCs and nanoweb substrates, which upregulated the expression and activation of voltage-gated ion channels in hfNSCs and further increased the effect of photoactive substrates on neuronal differentiation of hfNSCs. Conclusion The photoactive nanoweb substrates developed in this study may serve as platforms for producing stem cell therapeutics with enhanced neurogenesis and neuromodulation via optoelectrical control of stem cells.
30 citations
Cites background or methods from "Mass production of a 3D non-woven n..."
...photocurrent in bulk-heterojunction and bilayer organic solar cells [19, 22]....
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...The degree of electron transfer from P3HT to the electron acceptor depends on the interface area between the electron donor (P3HT) and acceptor (stem cells), as the exciton generated by light in P3HT is separated by the interface of the electron donor and acceptor [22]....
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...The P3HT substrates were prepared as reported previously [22]....
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References
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TL;DR: In this article, a review of the recent advances in organic electronics based on polymer blends with one-dimensional (1D) nanowires (NWs) of π-conjugated polymers is presented.
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69 citations
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59 citations
TL;DR: In this article, the authors demonstrated that interconnected nanofibrillar networks of poly(3-hexylthiophene) (P3HT) thin films with improved crystallinity can be easily fabricated by aging the precursor solution with marginal solvent.
Abstract: We demonstrated that interconnected nanofibrillar networks of poly(3-hexylthiophene) (P3HT) thin films with improved crystallinity can be easily fabricated by aging the precursor solution with marginal solvent. Structural analysis revealed that these benefits arise from the improvements in the crystallinity of P3HT in the precursor solution. At dilute concentrations, P3HT molecules grew into near-spherical particles during the aging time. As the aging time increased further, P3HT molecules exhibited one-dimensional growth into rod-like structures. At higher P3HT concentrations and longer P3HT solution aging times, dense nanowires were observed to form gradually, thereby improving the electronic properties of field-effect transistors (FETs) based on these films. This improvement was due to the change in P3HT organization in the precursor solution from a random-coil conformation to an ordered aggregate as a result of aging in a marginal solvent, methylene chloride. At high temperatures, the P3HT molecules were completely solvated and adopted a random-coil conformation, as is observed in good solvents. Whereas upon aging the solution at room temperature, methylene chloride poorly solvated the P3HT molecules such that ordered aggregates of P3HT grew in solution, which improved the molecular ordering of P3HT thin films produced from these solutions. The field-effect mobility of the thin films was, therefore, enhanced without the need for post-treatments.
59 citations
TL;DR: In this article, a method for the controlled, sequential design of a bilayer polymer cell architecture that consists of a large interface area with connecting paths to the respective electrodes for both materials is presented.
Abstract: Significant progress is being made in the photovoltaic energy conversion using organic semiconducting materials. One of the focuses of attention is the morphology of the donor−acceptor heterojunction at the nanometer scale, to ensure efficient charge generation and loss-free charge transport at the same time. Here, we present a method for the controlled, sequential design of a bilayer polymer cell architecture that consists of a large interface area with connecting paths to the respective electrodes for both materials. We used the surface-directed demixing of a donor conjugated/guest polymer blend during spin coating to produce a nanostructured interface, which was, after removal of the guest with a selective solvent, covered with an acceptor layer. With use of a donor poly(p-phenylenevinylene) derivative and the acceptor C60 fullerene, this resulted in much-improved device performance, with external power efficiencies more than 3 times higher than those reported for that particular material combination s...
54 citations
TL;DR: In this article, the effects of annealing time on the morphology of phase separation and charge transfer behavior inside the active layers of polymer solar cells are investigated using Monte Carlo simulations, and a suitably defined correlation distance is an effective parameter that quantitatively characterizes different morphologies and can be used to establish a direct link with transmission electron microscopy images.
Abstract: Morphology is a crucially important factor determining the efficiency of photocurrent generation in bulk heterojunction polymer solar cells. Morphology, which depends on the characteristics of the polymers as well as on the conditions of phase separation, affects the performance of solar cells by influencing the rate of exciton dissociation and the efficiency of charge carrier transport. Using Monte Carlo simulations, we investigate the effects of annealing time on the morphology of phase separation and charge transfer behavior inside the active layers of polymer solar cells. We find that a suitably defined correlation distance is an effective parameter that quantitatively characterizes different morphologies and can be used to establish a direct link with transmission electron microscopy images of real polymer solar cells. Optimal morphologies have been investigated, showing results that are consistent with experimental data.
47 citations