This work investigates the long term durability of polymer based electrochromic devices (ECDs) under simulated sunlight and elevated temperatures. PEDOT EthC6 served as a model polymer to elucidate fundamental degradation mechanisms and to develop strategies for improved cycling stability. The results address photostability, thermal stability, and charge balancing. Photostability was examined using UV Vis and IR spectroscopy. In an inert atmosphere, PEDOT EthC6 showed a 30% higher stability compared to air, while other factors had no detectable influence. IR analysis identified the terminal double bond of the side chain as a key site of photodegradation. Long pass filters were evaluated to determine optimal cut off wavelengths. Ni oxide was introduced as a counter electrode providing simultaneous photoprotection. These hybrid ECDs showed no loss in transmittance modulation after 350 h of irradiation. Thermal stability of PEDOT-EthC6/Prussian blue ECDs was assessed through cycling at elevated temperatures. At 60 °C, the performance initially decreased due to the formation of Prussian green. Temperature dependent cyclic voltammetry (CV) measurements confirmed this side reaction. For PEDOT EthC6, the CVs revealed a degradation of one subpopulation. The onset potentials of side reactions were determined and translated into safe switching voltages, enabling stability over 10 000 cycles at 60 °C. To study the influence of charge balancing, three PEDOT EthC6 film thicknesses used in hybrid ECDs with Ni oxide. The best performance was achieved when the polymer electrode was over dimensioned. This configuration limits the potential window at the polymer electrode, avoiding degradation prone regions, and ensures effective switching of the Ni oxide electrode. The ECDs were stable over 5 000 cycles at 25 °C and 65 °C. Overall, this thesis deepens the understanding of degradation pathways in polymeric ECDs and shows effective strategies to enhance their durability.
Lisa Brändler (Thu,) studied this question.