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We demonstrate that the observed (in-)stability of n-doped carbon nanotube films in air not only depends on the employed dopant but is also strongly affected by sample-specific factors, such as the film thickness and density. We show this for two typical dopants, polyethylenimine and a potassium crown ether complex, by preparing films of increasing thickness. We argue that reports on dopant stability cannot be properly assessed without knowledge of these sample-specific parameters, which explains some of the conflicting results in the literature.

The low endogenous regenerative capacity of the heart, added to the prevalence of cardiovascular diseases, triggered the advent of cardiac tissue engineering in the last decades. The myocardial niche plays a critical role in directing the function and fate of cardiomyocytes; therefore, engineering a biomimetic scaffold holds excellent promise. We produced an electroconductive cardiac patch of bacterial nanocellulose (BC) with polypyrrole nanoparticles (Ppy NPs) to mimic the natural myocardial microenvironment. BC offers a 3D interconnected fiber structure with high flexibility, which is ideal for hosting Ppy nanoparticles. BC-Ppy composites were produced by decorating the network of BC fibers (65 ± 12 nm) with conductive Ppy nanoparticles (83 ± 8 nm). Ppy NPs effectively augment the conductivity, surface roughness, and thickness of BC composites despite reducing scaffolds' transparency. BC-Ppy composites were flexible (up to 10 mM Ppy), maintained their intricate 3D extracellular matrix-like mesh structure in all Ppy concentrations tested, and displayed electrical conductivities in the range of native cardiac tissue. Furthermore, these materials exhibit tensile strength, surface roughness, and wettability values appropriate for their final use as cardiac patches. In vitro experiments with cardiac fibroblasts and H9c2 cells confirmed the exceptional biocompatibility of BC-Ppy composites. BC-Ppy scaffolds improved cell viability and attachment, promoting a desirable cardiomyoblast morphology. Biochemical analyses revealed that H9c2 cells showed different cardiomyocyte phenotypes and distinct levels of maturity depending on the amount of Ppy in the substrate used. Specifically, the employment of BC-Ppy composites drives partial H9c2 differentiation toward a cardiomyocyte-like phenotype. The scaffolds increase the expression of functional cardiac markers in H9c2 cells, indicative of a higher differentiation efficiency, which is not observed with plain BC. Our results hi

[Abstract] A combinatorial study of the effect of in-mixing of various guests on the thermoelectric properties of the host workhorse polymer poly[2,5-bis(3-tetradecylthiophen- 2-yl)thieno[3,2-b]thiophene] (PBTTT) is presented. Specifically, the composition and thickness for doped films of PBTTT blended with different polymers are varied. Some blends at guest weight fractions around 10–15% exhibit up to a fivefold increase in power factor compared to the reference material, leading to zT values around 0.1. Spectroscopic analysis of the charge-transfer species, structural characterization using grazing-incidence wide-angle X-ray scattering, differential scanning calorimetry, Raman, and atomic force microscopy, and Monte Carlo simulations are employed to determine that the key to improved performance is for the guest to promote long-range electrical connectivity and low disorder, together with similar highest occupied molecular orbital levels for both materials in order to ensure electronic connectivity are combined.

A combinatorial study of the effect of in-mixing of various guests on the thermoelectric properties of the host workhorse polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) is presented. Specifically, the composition and thickness for doped films of PBTTT blended with different polymers are varied. Some blends at guest weight fractions around 10–15% exhibit up to a fivefold increase in power factor compared to the reference material, leading to zT values around 0.1. Spectroscopic analysis of the charge-transfer species, structural characterization using grazing-incidence wide-angle X-ray scattering, differential scanning calorimetry, Raman, and atomic force microscopy, and Monte Carlo simulations are employed to determine that the key to improved performance is for the guest to promote long-range electrical connectivity and low disorder, together with similar highest occupied molecular orbital levels for both materials in order to ensure electronic connectivity are combined.

We present a method to dissolve carbon nanotubes that simultaneously allows to prepare n-doped films. These films are composed of thinner bundles of longer tubes when compared to films prepared using surfactants and sonication. Their negative Seebeck coefficient and high electrical conductivity make them good candidates for thermoelectric applications. We investigate their stability in air by aging them at elevated temperatures, showing stabilities over 500 h, which is further improved by the use of crown ethers. Finally, we demonstrate the usefulness of the prepared materials by fabricating an organic thermoelectric generator comprising 40 legs.

Coupling thermoelectrics (TE) with photovoltaics (PV) has emerged as an approach to solid-state solar harvesting, directly converting light and infrared heat into electricity. In this work, we compare PV-TE hybrid devices based on organic semiconductors in three different geometries: a reflection geometry, a non-contact transmission geometry, and a contact transmission geometry. The temperature rises of films of common organic thermoelectric materials, including poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), single-walled carbon nanotubes (swCNT), and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), were measured in configurations representative of the proposed geometries. Because organic semiconductors possess broadband light absorption and low thermal conductivities, a significant rise in temperature was observed under illumination for all geometries. We find, however, that the best configuration is, in fact, the transmission contact mode because it sums two effects. Operating under 1 sun illumination, the temperature of a commercial organic PV module increased by ≈30 K, which leads to an enhancement in OPV performance compared to room temperature. After attaching a thermoelectric to the OPV module, losses from convection are reduced, and the OPV module heats up even more, further increasing its efficiency while additionally enabling thermoelectric generation. Finally, we calculate theoretical thermoelectric efficiencies for the materials and their respective power densities.

Transition metal carbides have gathered increasing attention in energy and electrochemistry applications, mainly due to their high structural and physicochemical properties. Their high refractory properties have made them an ideal candidate coating technology and more recently their electronic similarity to the platinum group has expanded their use to energy and catalysis. Here, we demonstrate that the nanostructuring and stoichiometry control of the highest melting point material to this date (Ta-Hf-C) results in outstanding electrochemical stability. Our results show one of the largest windows of stability of a single component electrode in a broad range pH. These experiments provide a new perspective on the electrochemical, thermoelectric and mechanical behavior of Ta-Hf-C nanocomposites, towards a broad range of applications in energy production, catalysis and analytical chemistry.

Transfer printing is one of the key nanofabrication techniques for the large‐scale manufacturing of complex device architectures. It provides a cost‐effective and high‐throughput route for the integration of independently processed materials into spatially tailored architectures. Furthermore, this method enables the fabrication of flexible and curvilinear devices, paving the way for the fabrication of a new generation of technologies for optics, electronics, and biomedicine. In this work, hydroxypropyl cellulose (HPC) membranes are used as water soluble adhesives for transfer printing processes with improved performance and versatility compared to conventional silicone alternatives. The high‐water solubility and excellent mechanical properties of HPC facilitate transfer printing with high yield for both metal and carbon nanotubes (CNTs) inks. In the case of metal inks, crack‐free stripping of silver films and the simple fabrication of Moiré Plasmonic architectures of different geometries are demonstrated. Furthermore, HPC membranes are used to transfer print carbon nanotube films with different thicknesses and up to 77% transparency in the visible and near infrared region with potential applications as transparent conductive substrates. Finally, the use of prepatterned HPC membranes enables nanoscale patterning of CNT with feature resolution down to 1 µm.

The stability of organic semiconductors is an important topic, which in the case of organic thermoelectrics (OTEs), has not yet got the attention it deserves. This work presents a simple method which allows to characterize the stability of OTEs, using patterned ITO substrates to electrically contact encapsulated samples. The method is applied to n‐doped carbon nanotube films, a well‐suited reference system due to their sensitivity to changes in doping level, and used to compare the effectiveness of different encapsulation methods. In the observed films, oxygen adsorption leads to a gradual p‐doping. Among the investigated barrier materials, glass performs best. Flexible alternatives like transferred films of barrier polymers also show promise, while barrier films deposited by dropcast performed worse, likely due to their inhomogeneity. Finally, Raman imaging is shown to be a useful technique to investigate degradation in OTEs.

Two doping mechanisms are known for the well-studied materials poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), namely, integer charge transfer (ICT) and charge transfer complex (CTC) formation. Yet, there is poor understanding of the effect of doping mechanism on thermal stability and the thermoelectric properties. In this work, we present a method to finely adjust the ICT to CTC ratio. Using it, we characterize electrical and thermal conductivities as well as the Seebeck coefficient and the long-term stability under thermal stress of P3HT and PBTTT of different ICT/CTC ratios. We establish that doping through the CTC results in more stable, yet lower conductivity samples compared to ICT doped films. Importantly, moderate CTC fractions of ∼33% are found to improve the long-term stability without a significant sacrifice in electrical conductivity. Through visible and IR spectroscopies, polarized optical microscopy, and grazing-incidence wide-angle X-ray scattering, we find that the CTC dopant molecule access sites within the polymer network are less prone to dedoping upon thermal exposure.

Thermoelectricity offers a sustainable path to recover and convert waste heat into readily available electric energy, and has been studied for more than two centuries. From the controversy between Galvani and Volta on the Animal Electricity, dating back to the end of the XVIII century and anticipating Seebeck’s observations, the understanding of the physical mechanisms evolved along with the development of the technology. In the XIX century Ørsted clarified some of the earliest observations of the thermoelectric phenomenon and proposed the first thermoelectric pile, while it was only after the studies on thermodynamics by Thomson, and Rayleigh’s suggestion to exploit the Seebeck effect for power generation, that a diverse set of thermoelectric generators was developed. From such pioneering endeavors, technology evolved from massive, and sometimes unreliable, thermopiles to very reliable devices for sophisticated niche applications in the XX century, when Radioisotope Thermoelectric Generators for space missions and nuclear batteries for cardiac pacemakers were introduced. While some of the materials adopted to realize the first thermoelectric generators are still investigated nowadays, novel concepts and improved understanding of materials growth, processing, and characterization developed during the last 30 years have provided new avenues for the enhancement of the thermoelectric conversion efficiency, for example through nanostructuration, and favored the development of new classes of thermoelectric materials. With increasing demand for sustainable energy conversion technologies, the latter aspect has become crucial for developing thermoelectrics based on abundant and non-toxic materials, which can be processed at economically viable scales, tailored for different ranges of temperature. This includes high temperature applications where a substantial amount of waste energy can be retrieved, as well as room temperature applications where small and local temperature

Thermoelectrics have emerged as a strategy for solar‐to‐electricity conversion, as they can complement photovoltaic devices as IR harvesters or operate as stand‐alone systems often under strong light and heat concentration. Inspired by the recent success of inorganic‐based solar thermoelectric generators (STEGs), in this manuscript, the potential of benchmark organic thermoelectric materials for solar harvesting is evaluated. It is shown that the inherent properties of organic semiconductors allow the possibility of fabricating organic STEGs (SOTEGs) of extraordinary simplicity. The broadband light absorption exhibited by most organic thermoelectrics combined with their low thermal conductivities results in a significant temperature rise upon illumination as seen by IR thermography. Under 2 sun illumination, a temperature difference of 50 K establishes between the illuminated and the non‐illuminated sides of a poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film, and ≈40 K for a carbon nanotube/cellulose composite. Moreover, when using light as a heat source, the Seebeck coefficient remains unaffected, while a small photoconductivity effect is observed in PEDOT:PSS and carbon nanotubes. Then, the effect of several geometrical factors on the power output of a solar organic thermoelectric generator is investigated, enabling us to propose simple SOTEG geometries that capitalize on the planar geometry typical of solution‐processable materials. Finally, a proof‐of‐concept SOTEG is demonstrated, generating 180 nW under 2 suns.

Thermoelectricity offers a sustainable path to recover and convert waste heat into readily available electric energy, and has been studied for more than two centuries. From the controversy between Galvani and Volta on the Animal Electricity, dating back to the end of the XVIII century and anticipating Seebeck’s observations, the understanding of the physical mechanisms evolved along with the development of the technology. In the XIX century Ørsted clarified some of the earliest observations of the thermoelectric phenomenon and proposed the first thermoelectric pile, while it was only after the studies on thermodynamics by Thomson, and Rayleigh’s suggestion to exploit the Seebeck effect for power generation, that a diverse set of thermoelectric generators was developed. From such pioneering endeavors, technology evolved from massive, and sometimes unreliable, thermopiles to very reliable devices for sophisticated niche applications in the XX century, when Radioisotope Thermoelectric Generators for space missions and nuclear batteries for cardiac pacemakers were introduced. While some of the materials adopted to realize the first thermoelectric generators are still investigated nowadays, novel concepts and improved understanding of materials growth, processing, and characterization developed during the last 30 years have provided new avenues for the enhancement of the thermoelectric conversion efficiency, for example through nanostructuration, and favored the development of new classes of thermoelectric materials. With increasing demand for sustainable energy conversion technologies, the latter aspect has become crucial for developing thermoelectrics based on abundant and non-toxic materials, which can be processed at economically viable scales, tailored for different ranges of temperature. This includes high temperature applications where a substantial amount of waste energy can be retrieved, as well as room temperature applications where small and local temperature

Esta tesis explora cómo las interacciones entre materiales orgánicos pueden ser aprovechadas para obtener funcionalidad adicional de una manera sencilla, sin necesidad de procesamiento complejo. Los resultados obtenidos tienen aplicaciones en el campo de la fotovoltaica y termoeléctrica orgánica. El trabajo se centra en materiales tales como polímeros conjugados y nanotubos de carbono, y procesos de deposición desde disolución simples, como el recubrimiento por cuchilla. La primera parte presenta resultados sobre la caracterización elipsométrica de las propiedades ópticas de los polímeros conjugados y sus mezclas con fullerenos o dopantes. La elipsometría espectroscópica de ángulo variable se utilizó no sólo para caracterizar las constantes ópticas de nuevos polímeros altamente absorbentes, sino también para investigar el efecto de los aditivos disolventes sobre el grado de segregación vertical de fase en mezclas de polímero:fullereno. La segunda parte detalla el trabajo sobre nanocompuestos de polímeros conjugados y nanotubos de carbono, una prometedora clase de materiales termoeléctricos orgánicos. Debido a que los polímeros conjugados permiten desenredar los manojos de nanotubos de carbono de manera eficiente, estos nanocompuestos se pueden preparar fácilmente. Presentan tanto una buena conductividad eléctrica como una baja conductividad térmica, que son requisitos necesarios para un buen rendimiento termoeléctrico. De particular interés son los compuestos de tipo n que contienen nanotubos de carbono dopados con nitrógeno, así como métodos de procesamiento que permiten cambiar el tipo de portador mayoritario. La tercera parte se centra en técnicas sencillas de fabricación de dispositivos fotovoltaicos orgánicos, con el objetivo particular de obtener capas orientadas de polímeros conjugados. Esto se logró controlando localmente la evaporación del disolvente para influir en la cristalización epitaxial direccional de polímeros conjugados en un aditivo disolvente cri, This thesis explores ways of how interactions between organic materials can be exploited to obtain additional functionality in a simple manner, without the need for complex processing. The obtained results have applications in the field of organic photovoltaics and thermoelectrics. The work focuses on materials such as conjugated polymers and carbon nanotubes, and simple solution-based deposition processes such as blade coating. The first part presents results on the ellipsometric characterization of the optical properties of conjugated polymers and their blends with fullerenes or dopants. Variable angle spectroscopic ellipsometry was used not only to characterize the optical constants of new, highly absorbing polymers, but also to investigate the effect of solvent additives on the degree of vertical phase segregation in polymer:fullerene blends. The second part details the work on nanocomposites of conjugated polymers and carbon nanotubes, a promising class of organic thermoelectric materials. Because conjugated polymers allow for efficient debundling of carbon nanotubes, these nanocomposites can be prepared readily. They exhibit both a good electrical conductivity and a low thermal conductivity, which are necessary requisites for good thermoelectric performance. Of particular interest are n-type composites containing nitrogen-doped carbon nanotubes, as well as processing methods that allow to change the majority carrier type. The third part focuses on simple fabrication techniques for organic photovoltaic devices, with the particular objective of obtaining oriented layers of conjugated polymers. This was achieved by locally controlling solvent evaporation to influence the directional epitaxial crystallization of conjugated polymers on a crystalline solvent additive. The developed method allows to prepare two distinct types of films. If the nucleation of the additive is confined to the one-dimensional contact line during blade-coating, then uniaxially oriented film

The invention relates to a process of obtainment of an n-type or a p-type organic semiconductor by irradiating a p-type or an n-type organic semiconductor with UV-VIS radiation, respectively.

The nucleation of single macroscopic spherulites at desired positions, as well as ordered arrays of multiple spherulites, is demonstrated by combining the use of crystallizable solvents with local control of solvent evaporation during solution deposition. Moreover, the temperature assisted localized frustration of molecular orientation is shown, enabling the fabrication of samples containing both isotropic areas and spherulites. These macroscopic circular polycrystalline structures are characterized using a range of polarized spectroscopic techniques that allow quantifying their large degree of chain orientation. In order to show the potential of these large conjugated polymer spherulites centered at desired locations, graded bilayer organic photovoltaic devices were fabricated to be used as polarimeters, solid state light polarization detectors with no moving parts, and position sensitive photodetectors.

This work compares various methods to prepare polymer/carbon nanotube (CNT) composites for thermoelectric applications, focusing on the different doping mechanisms. We first look at the general trends observed in the Seebeck coefficient and power factor for a large number of composites as a function of electrical conductivity. Then we discuss two methods of nitrogen doping the carbon nanotubes in these composites, namely either during synthesis, or afterwards by ammonolysis. Finally, we discuss doping of the carbon nanotubes through charge transfer from the polymer counterpart, including photo-induced switching of the majority carrier type. As a general remark, we note that processability is negatively influenced by some doping procedures. Best results were achieved for unfunctionalized single-walled carbon nanotubes with a high content of semiconducting CNT species.

The specific optical absorption of an organic semiconductor is critical to the performance of organic optoelectronic devices. For example, higher light-harvesting efficiency can lead to higher photocurrent in solar cells that are limited by sub-optimal electrical transport. Here, we compared over 40 conjugated polymers, and found that many different chemical structures share an apparent maximum in their extinction coefficients. However, a diketopyrrolopyrrole-thienothiophene copolymer shows remarkably high optical absorption at relatively low photon energies. By investigating its backbone structure and conformation with measurements and quantum chemical calculations, we find that the high optical absorption can be explained by the high persistence length of the polymer. Accordingly, we demonstrate high absorption in other polymers with high theoretical persistence length. Visible light harvesting may be enhanced in other conjugated polymers through judicious design of the structure.

UV-induced switching from p- to n-type character is demonstrated during deposition of carbon-nanotube–conjugated polymer composites. This opens the possibility to photopattern n-type regions within an otherwise p-type film, which has a potential for complementary circuitry or, as shown here, thermoelectric generators made from a single solution.

Using chlorobenzene as a base solvent for the deposition of the poly(3-hexylthiophene-2,5-diyl) (P3HT) layer in P3HT:phenyl-C61-butyric acid methyl ester diffusive bilayer solar cells, we investigate the effect of adding of small amounts of high-boiling-point solvents with similar chemical structures on the resulting active layer morphologies. The results demonstrate that the crystallinity of the P3HT films as well as the vertical donor–acceptor gradient in the active layer can be tuned by this approach. The use of high-boiling-point solvents improved all photovoltaic parameters and resulted in a 32% increase in power conversion efficiency., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/14051