Organic semiconductors offer numerous advantages over inorganic semiconductors, including cost-effective fabrication, a versatility of applications, and an environmentally sustainable alternative. Among these materials, conjugated polymers suggest promising results. Conjugated polymers rely on dopants to produce charge carriers, but dopants also create an unanticipated tradeoff between trapped and free carriers, changes to the electronic structure and packing of the polymer, and instability of the material properties over time. In this dissertation, I explored different methods to study the effects of dopants in a variety of systems, including pristine polymers and blends of polymers with other polymers, small molecules, and nanoparticles. We primarily studied thermoelectric properties such as Seebeck coefficient and electrical conductivity since they depend on the doping level and are sensitive to the chemical structure, electronic structure, and morphology of the material. Our work contributed to unrevealing the role of dielectric permittivity, types of morphologies, and other aspects of conjugated polymers in charge transport. We pave the way towards a holistic material design that favors dopant-generated free carriers but also eliminates many detrimental dopant-induced effects.