[en] Conjugated polymers are promising materials for flexible electronics and organic photovoltaics due to their lightweight, flexible nature, and cost-effectiveness. In the field of heat-to-electricity conversion, conjugated polymers are being extensively considered as promising thermoelectric materials due to their intrinsically low thermal conductivity and reasonable Seebeck coefficients. Enhancing the electrical conductivity towards efficient thermoelectrics based on conjugated polymers has been the focus of significant research efforts, including fine optimization through extensive studies on doping processing techniques and synthesis of novel efficient dopants. However, a comprehensive understanding of the correlation between the doping, doping-introduced morphological changes, and the resulting thermoelectric properties-particularly thermal conductivity-has received relatively limited attention thus far. This is, in part, due to the complex microstructures exhibited by conjugated polymer thin films, and its dependency on factors such as processing steps and material properties (e.g. molecular weight). In this thesis, we comprehensively investigate the impact of doping, molecular weight blending and molecular length on the morphology and the resulting thermoelectric properties of conjugated polymers, with a particular focus on thermal conductivity. The first set of results reports on the impact of doping on thermal conductivity based on eight polymers and four doping systems. We observed that upon doping, the out-of-plane component of the thermal conductivity of five polymers with relatively high structure order is reduced compared to the corresponding value for the neat polymers. We investigated several hypotheses to understand this behavior: (i) an increase in intrinsic thermal anisotropy due to in-plane orientation of the backbones, (ii) a modification in the crystalline to amorphous fraction, and (iii) an alloying effect resulting from the introduction of the dopant. Through various structural analysis techniques, including Grazing Incidence Wide Angle X-Ray (GIWAXS), Raman and infrared spectroscopy, we correlated structural and thermal properties, demonstrating a direct influence of in-plane alignment of their backbones on both the in-plane and out-of-plane components of thermal conductivity. Furthermore, through specifically designed experiments based on photolysis reaction, we demonstrated that the shortening of the polymer's backbones significantly impacts thermal conductivity. Therefore, the subsequent chapter centered on the impact of average molecular weight on morphology and the resultant thermal and electrical transport within polymers. By blending P3HTs with two different molecular weights in distinct ratios, we first investigated the impact of molecular weight on the microstructure and thermal transport in the pristine samples. Following this, we characterized the thermoelectric performance of the doped samples as a function of molecular weight. The correlation between the microstructure, doping, thermal conductivity and electron conductivity is discussed in this chapter. In the following chapter, we studied the impact of polymer molecular length on morphology and the resulting thermal and electrical transport properties using seven synthesized oligomers with gradually increasing molecular lengths. GIWAXS, photoluminescence, and UV-Vis spectroscopy were utilized to establish morphological changes across the various molecular lengths. An imaging approach was employed to accurately assess the overall homogeneity of thermal conductivity across different positions within the samples. Additionally, building on the room-temperature data of oligomers, we extended our study to temperature-dependent measurements. Consequently, we characterized the temperature-dependent thermal conductivity as a function of molecular weight and analyzed the morphological changes across different temperatures using PL. In conclusion, this thesis demonstrates the effects of doping on the thermoelectric properties of conjugated polymers and highlights the intricate relationships between molecular weight, morphology, doping, temperature, and thermal transport.

[es] Los polímeros conjugados son materiales prometedores para la electrónica flexible y la fotovoltaica orgánica por su ligereza, flexibilidad y rentabilidad. En el ámbito de la conversión de calor en electricidad, se consideran materiales termoeléctricos prometedores gracias a su baja conductividad térmica y buenos coeficientes de Seebeck. Mejorar la conductividad eléctrica de los polímeros conjugados ha sido un objetivo de investigación clave, centrándose en el dopaje y la síntesis de nuevos dopantes. Sin embargo, la correlación entre el dopaje, los cambios morfológicos y las propiedades termoeléctricas, especialmente la conductividad térmica, ha recibido poca atención hasta ahora. Esta tesis investiga el impacto del dopaje, la mezcla de pesos moleculares y la longitud molecular en la morfología y las propiedades termoeléctricas de los polímeros conjugados, con especial énfasis en la conductividad térmica. Los resultados muestran que el dopaje reduce la conductividad térmica en polímeros con alto orden estructural, sugiriendo una mayor anisotropía térmica y cambios en la fracción cristalina en amorfa. También se ha demostrado que el acortamiento de la columna vertebral del polímero afecta significativamente a la conductividad térmica. Además, se estudió el impacto del peso molecular medio en la morfología y el transporte térmico y eléctrico, mezclando P3HT con distintos pesos moleculares. Se investigó la correlación entre la microestructura, el dopaje y las conductividades térmica y eléctrica. También se estudió el impacto de la longitud molecular del polímero en la morfología y las propiedades de transporte utilizando oligómeros de distintas longitudes. En conclusión, esta tesis demuestra cómo el dopaje afecta a las propiedades termoeléctricas de los polímeros conjugados, destacando la relación entre el peso molecular, la morfología, la temperatura y el transporte térmico.