Computational Spectroscopy of D18 Photodegradation

Sammanfattning

Historically, the main challenges in the field of organic photovoltaics (OPV) have been low efficiency and stability. With the development of non-fullerene acceptors (NFA), OPV designs have reached commercially viable efficiencies of close to 20%, but operational stability continues to be problematic. In this work, a simplified molecular model for the OPV donor polymer D18 was implemented to determine the optical and excited state properties of this photoactive material. The same principles were then used to model three possible photodegradation products of D18, based on a proposed photodegradation mechanism involving the opening of a thiophene ring followed by oxidation. The spectroscopic properties of the pristine and photodegraded D18 models were investigated and compared to experimental data. Other electronic properties, such as particle and hole densities, were also studied, showing a distinct change in delocalization of the densities by breaking the conjugation at the photodegradation site. Finally, X-ray absorption spectroscopy was suggested as an experimental method for verifying the presence of these specific photodegradation products in D18 samples.