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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Journal Article•
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: P3HT/PCBM bilayers are used as a model to investigate the interdiffusion of the components and its role in the development of the morphology and results indicated that one phase is an ordered P3HT domain and the other phase is the mixture of amorphous P3 HT and PCBM which is not consistent with a phase separation of the component by a spinodal decomposition mechanism.
Abstract: To better understand the physics of the photoactive layer in the organic photovoltaic devices, it is necessary to gain a quantitative understanding of the morphology and the manner in which it develops. A key element in the kinetics associated with the structure development is the interdiffusion of the components. To that end we used P3HT/PCBM bilayers as a model to investigate the interdiffusion of the components and its role in the development of the morphology. A detailed description of the diffusion behavior and the morphology developed from a layer of P3HT in contact with a layer of PCBM during thermal annealing is given. Amorphous P3HT and PCBM are shown to be highly miscible and PCBM can penetrate into the P3HT layer through the P3HT amorphous region and form the bulk heterojunction structure within a few seconds of annealing at 150 °C. The results indicated that one phase is an ordered P3HT domain and the other phase is the mixture of amorphous P3HT and PCBM which is not consistent with a phase separation of the components by a spinodal decomposition mechanism.
291 citations
TL;DR: In this article, the authors provide an overview of recent advances in the characterisation of conjugated polymer blend nanostructure and developments in the linking of blend structure and device performance.
Abstract: The blending of two semiconducting polymers with offset energy levels enables efficient charge generation in thin-film ‘all-polymer’ solar cells. A key requirement for efficient charge separation and collection is the formation of interconnected phase-separated domains structured on the sub-20 nm length-scale. This review provides an overview of recent advances in the characterisation of conjugated polymer blend nanostructure and developments in the linking of blend structure and device performance. This review also provides a general introduction to the polymer physics behind phase separation, experimental techniques used for characterising blend structure and novel ways to control nanomorphology.
280 citations
TL;DR: In this article, a helical conformation of the man chain of poly(3-alkylthiophene)s with 12 thiophene rings per each helical turn has been proposed.
Abstract: Solvent-induced aggregation of regioregular head-to-tail poly(3-alkylthiophene)s (PATs) have been studied by means of AFM and UV−vis spectroscopy. In hexane, which is a good solvent for alkyl side chains but poor for polythiophene backbones, PAT molecules undergo ordered main-chain collapse driven by solvophobic interaction. Well-pronounced concentration-independent red shift of λmax and good resolved fine vibronic structure in the electronic absorption spectra observed upon addition of hexane indicate that planarization occurs on the single-molecule level. A helical conformation of the man chain of PATs with 12 thiophene rings per each helical turn has been proposed. At the higher concentration of PATs the collapsed molecules undergo unexpected one-dimensional aggregation. Length of the particles varies from several nanometers to several hundreds nanometers and can be easily adjusted by the solvent composition or concentration of PATs.
246 citations
TL;DR: The evolution of the vertical morphology in a solution-processed P3HT/PCBM "bilayer" organic solar cell is investigated using a combination of techniques, including neutron reflectometry, and it is established that the solution processed bilayer concept is a misnomer.
Abstract: We investigate the evolution of the vertical morphology in a solution-processed P3HT/PCBM "bilayer" organic solar cell using a combination of techniques, including neutron reflectometry. By correlating the device performance with the active layer morphology, we establish that the solution processed bilayer concept is a misnomer and sequential solution processing is an elegant way to make bulk heterojunction organic solar cells with high efficiency.
233 citations
Journal Article•
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