Unlocking intrinsic stretchability in PM6-based materials for next-generation solar cells: challenges and innovations

In the rapidly evolving field of wearable electronics, stretchy organic solar cells (OSCs) have emerged as promising candidates for portable power sources, necessitating materials with superior mechanical flexibility. However, the inherent rigidity of conjugated backbones in top-performance photovoltaic polymers, such as PM6, poses a significant challenge, as it makes photovoltaic films prone to fracture under mechanical strain. Consequently, improving the mechanical properties of these films is a crucial research frontier for advancing stretchable photovoltaic technologies. This tutorial review provides a thorough examination of current strategies aimed at bolstering the mechanical resilience of polymer photovoltaic thin films, elucidated through a selection of pertinent examples leveraging the PM6-based systems. We first explore the prevalent strategy of incorporating third components, including guest polymer donors/acceptors and insulating polymers, to improve stretchability. We then discuss the structural design of PM6 aimed at reducing the backbone rigidity. Additionally, we summarize various predictive models for assessing the mechanical properties of these photovoltaic films. Finally, the future challenges and perspectives for stretchy OSCs are explored.