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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

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., Funding Agencies|Spanish Ministry of Science and InnovationSpanish Government [CEX2019-000917-S, PGC2018-095411- B-I00, PGC2018-094620-A-I00, MAT2017-90024-P]; European Research Council (ERC)European Research Council (ERC)European Commission [648901, 963954]; Ministerio de Ciencia, Innovacion y UniversidadesSpanish Government; European Regional Development FundEuropean Commission; European Social FundEuropean Social Fund (ESF); CSIC Open Access Publication Support Initiative through its Unidad de Recursos de Informacion Cientifica para la Investigacion (URICI); Carl Zeiss Foundation; Alexander von Humboldt FoundationAlexander von Humboldt Foundation

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.

En l'actual era de la Internet de les Coses (de l'anglès, IOT), els dispositius de detecció intel·ligents estan canviant molt el món en què vivim, des de com percebem el nostre entorn fins a com gastem l'energia. Fonts d'energia per a aquests dispositius seran essencials, especialment si no requereixen manteniment, són flexibles, barates, altament processable o fins i tot d'un sol ús. Els materials termoelèctrics orgànics --- semiconductors que poden transformar la calor en electricitat --- poden complir aquestes característiques. No obstant això, en els materials d'última generació encara hi ha aspectes que necessiten ser millorats; com el rendiment termoelèctric, estimat mitjançant la figura de mèrit ZT i l'estabilitat termoelèctrica sota continu estrès tèrmic. Aquesta tesi informa sobre estratègies per millorar l'eficiència i estabilitat termoelèctriques. Com a sistema de referència fem servir PBTTT dopat amb l'acceptor molecular F4TCNQ. Com a eina transversal per als nostres estudis, desenvolupem mètodes de fabricació i caracterització d'alt rendiment basats en gradients de tractament tèrmic, dopat i gruix per estudiar i correlacionar la relació entre la microestructura, les propietats termoelèctriques i l'estabilitat en una gran quantitat de mostres. A la primera secció de resultats proposem una estratègia per millorar l'estabilitat termoelèctrica. Hem demostrat que la formació de complexos de càrrega (CTC per les seves sigles en anglès) generen mostres tèrmicament més resistents, encara que elèctricament menys conductores. Al desenvolupar un mètode per ajustar la relació de transferència de càrrega parcial a una transferència completa, podem millorar l'estabilitat a llarg termini sense sacrificar la conductivitat elèctrica. La segona secció de resultats aborda la relació entre la cristal·linitat, el transport tèrmic i el transport elèctric. Hem demostrat que el grau de cristal·linitat determina en gran mesura la conductivitat tèrmica de capa fina de polímer. U, En la actual era de la Internet de las Cosas (del inglés, IoT), los dispositivos de detección inteligentes están cambiando mucho del mundo en el que vivimos, desde cómo percibimos nuestro entorno hasta cómo gastamos la energía. Fuentes de energía para tales dispositivos serán esenciales, especialmente si no requieren mantenimiento, son flexibles, baratas, altamente procesable o incluso desechables. Los materiales termoeléctricos orgánicos --- semiconductores que pueden transformar el calor en electricidad --- pueden cumplir estas características. Sin embargo, en los materiales de última generación todavía hay aspectos que necesitan ser mejorados; como el rendimiento termoeléctrico, estimado mediante la figura de mérito ZT y la estabilidad termoeléctrica bajo continuo estrés térmico. Esta tesis informa sobre estrategias para mejorar la eficiencia y estabilidad termoeléctricas. Como sistema de referencia empleamos PBTTT dopado con el aceptor molecular F4TCNQ. Como herramienta transversal para nuestros estudios, desarrollamos métodos de fabricación y caracterización de alto rendimiento basados en gradientes de tratamiento térmico, dopado y espesor para estudiar y correlacionar la relación entre la microestructura, las propiedades termoeléctricas y la estabilidad en una gran cantidad de muestras. En la primera sección de resultados proponemos una estrategia para mejorar la estabilidad termoeléctrica. Demostramos que la formación de complejos de carga (CTC) generan muestras térmicamente más resistentes, aunque menos eléctricamente menos conductora. Al desarrollar un método para ajustar la relación de transferencia de carga parcial a entera, podemos mejorar la estabilidad a largo plazo sin sacrificar la conductividad eléctrica. La segunda sección de resultados aborda la relación entre cristalinidad, transporte térmico y eléctrico. Demostramos que el grado de cristalinidad determina en gran medida la conductividad térmica de capa fina de polímero. Tras dopar, incluso un co, In the current Internet of Things (IoT) era, smart sensing-devices are changing much about the world we live in, from how we sense our surroundings to the way we spend energy. On-site power generators for such devices will be essential, especially if they are maintenance-free, flexible, cheap, printable, or even disposable. Organic thermoelectric materials --- semiconductors that can transform heat into electricity at near-room temperature --- can fulfill these characteristics. Nevertheless, there are still issues in the current state-of-the-art materials that need improvement, such as the thermoelectric performance, benchmarked by the dimensionless ZT, and the thermoelectric stability under continuous thermal stress. This thesis reports on strategies to improve thermoelectric efficiency and stability. As a testbed material system, we employ PBTTT doped with the molecular acceptor F4TCNQ. As a transversal tool for our studies, we developed high-throughput fabrication and characterization methods based on annealing-, doping- and thickness-gradients to study and correlate the relationship between microstructure, thermoelectric properties, and stability for many samples. The first set of results reports on a strategy to improve thermoelectric stability. We demonstrate that the formation of charge transfer complexes (CTCs) leads to more thermally enduring samples, although less electrically conductive. By developing a method to adjust the partial to integer charge-transfer ratio, we can improve the long-term stability without sacrificing the electrical conductivity. The subsequent chapter centers on the relationship between crystallinity and thermal and electric transport. We demonstrate that the degree of crystallinity largely determines the thermal conductivity of the film. Upon doping, even a relatively small dopant content increases the electrical conductivity several orders of magnitude but lowers the thermal conductivity without noticeable deterioration in the cry, Universitat Autònoma de Barcelona. Programa de Doctorat en Ciència de Materials

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.

Electronic doping in organic materials has remained an elusive concept for several decades. It drew considerable attention in the early days in the quest for organic materials with high electrical conductivity, paving the way for the pioneering work on pristine organic semiconductors (OSCs) and their eventual use in a plethora of applications. Despite this early trend, however, recent strides in the field of organic electronics have been made hand in hand with the development and use of dopants to the point that are now ubiquitous. Here, we give an overview of all important advances in the area of doping of organic semiconductors and their applications. We first review the relevant literature with particular focus on the physical processes involved, discussing established mechanisms but also newly proposed theories. We then continue with a comprehensive summary of the most widely studied dopants to date, placing particular emphasis on the chemical strategies toward the synthesis of molecules with improved functionality. The processing routes toward doped organic films and the important doping–processing–nanostructure relationships, are also discussed. We conclude the review by highlighting how doping can enhance the operating characteristics of various organic devices.

Strong synthetic and engineering efforts have taken the efficiency of non-fullerene acceptor (NFA) based organic solar cells above 18% in a few years. Nonetheless, a deep understanding of the fundamental properties of this class of molecules is still missing. Here, we systematically investigated the morphological properties of two high efficient indacenodithienothiophene-based NFAs - namely ITIC and ITIC-4F - in order to correlate the hydrogen/fluorination substitutions with the materials structural and stability properties. We confirm that each NFA structurally evolves with increasing temperature into several polymorphs, identifying through spectroscopy their corresponding narrow temperature ranges. We demonstrate that the materials' response to accelerated stress tests (ASTs) is both substitution and polymorph dependent. ASTs underlined that the most vulnerable molecular segment corresponds to the thienothiophene C?C bond along the central backbone, together with the C?C linkage between the electron-rich donor and the electron-deficient acceptor moieties, with a degradation process triggered by oxygen and light. ITIC-4F showed lower oxidation capability and a higher bond strength retaining effect compared to ITIC. Lastly, the AST approach employed here allowed for the extrapolation of morphological and stability-related features within a high-throughput framework, and can be considered as a valuable methodological tool for future stability-related studies

Here we show that molecular doping of polymer thermoelectrics increases the electrical conductivity while reducing the thermal conductivity. A high-throughput methodology based on annealing and doping gradients within individual films is employed to self-consistently analyze and correlate electrical and thermal characteristics for the equivalent of >100 samples. We focus on the benchmark material system poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) doped with molecular acceptor 2,3,5,6-tetrafittoro-7,7,8,8-tetra-cyanoquinodimethane (F4TCNQ). The thermal conductivity of neat PBTTT films is dominated by the degree of crystallinity, with thermal percolation observed for annealing temperatures >170 degrees C. Upon doping the samples with a relatively low amount of F4TCNQ (anion content <1 mol %), the thermal conductivity exhibits a two-fold reduction without compromising the crystalline quality, which resembles the effect of alloy scattering observed in several inorganic systems. The analysis of the relation between thermal and electrical conductivities shows that thermal transport is dominated by a doping-induced reduced lattice contribution.

Strong synthetic and engineering efforts have taken the efficiency of non-fullerene acceptor (NFA) based organic solar cells above 18% in a few years. Nonetheless, a deep understanding of the fundamental properties of this class of molecules is still missing. Here, we systematically investigated the morphological properties of two high efficient indacenodithienothiophene-based NFAs – namely ITIC and ITIC-4F – in order to correlate the hydrogen/fluorination substitutions with the materials structural and stability properties. We confirm that each NFA structurally evolves with increasing temperature into several polymorphs, identifying through spectroscopy their corresponding narrow temperature ranges. We demonstrate that the materials’ response to accelerated stress tests (ASTs) is both substitution and polymorph dependent. ASTs underlined that the most vulnerable molecular segment corresponds to the thienothiophene C[double bond, length as m-dash]C bond along the central backbone, together with the C[double bond, length as m-dash]C linkage between the electron-rich donor and the electron-deficient acceptor moieties, with a degradation process triggered by oxygen and light. ITIC-4F showed lower oxidation capability and a higher bond strength retaining effect compared to ITIC. Lastly, the AST approach employed here allowed for the extrapolation of morphological and stability-related features within a high-throughput framework, and can be considered as a valuable methodological tool for future stability-related studies.

Here we show that molecular doping of polymer thermoelectrics increases the electrical conductivity while reducing the thermal conductivity. A high-throughput methodology based on annealing and doping gradients within individual films is employed to self-consistently analyze and correlate electrical and thermal characteristics for the equivalent of >100 samples. We focus on the benchmark material system poly(2,5- bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) doped with molecular acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). The thermal conductivity of neat PBTTT films is dominated by the degree of crystallinity, with thermal percolation observed for annealing temperatures >170 °C. Upon doping the samples with a relatively low amount of F4TCNQ (anion content <1 mol %), the thermal conductivity exhibits a two-fold reduction without compromising the crystalline quality, which resembles the effect of alloy scattering observed in several inorganic systems. The analysis of the relation between thermal and electrical conductivities shows that thermal transport is dominated by a doping-induced reduced lattice contribution.

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.

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.