Excited State Photodegradation of Organic Photovoltaic Materials

Stability or lack thereof is currently the Achilles heel of organic photovoltaics, which is otherwise close to reaching a power conversion efficiency of 20% and can already be processed using scalable manufacturing approaches using green and sustainable materials. Photodegradation is only empirically studied, is not well understood, and there continue to be widely held misconceptions about the effectiveness of encapsulation whereby it is thought that effective blocking of O₂, H₂O and UV can address photodegradation. Unfortunately, modern donor and acceptor materials photodegrade in inert atmosphere under visible light illumination simply by being in the excited state, pointing to inherent photostability issues associated to the excitonic nature of conjugated materials that must be understood at a fundamental level and then mitigated either through material design or through engineering of the photophysics and photochemistry within the BHJ layer. In this talk, we will present our understanding of excited state photodegradation of conjugated materials in inert atmosphere and how this is directly associated to excited state lifetime in materials. We will demonstrate how photodegradation is dependent on the chemical resilience of various molecular classes and ways to mitigate photodegradation in inert atmosphere through judicious design of quenching approaches, including in bulk heterojunction films.