Organic solar cells (OSCs) have garnered significant interest for potential commercial uses because of their light weight, mechanical flexibility, semitransparency, and large-area manufacturing properties. In the past few years, the efficiency of organic solar cells (OSCs) has greatly improved owing to the emergence of Y-series non-fullerene acceptors (Y-NFAs) and the advancements in polymer donors. Given the rapid progress in efficiency, it becomes crucial to prioritize the examination of the stability of photovoltaic materials. These materials play an important role in determining the lifetime of OSCs under real-world conditions, ensuring they meet the necessary criteria for future commercialization. However, the connection between the molecular structure and the outdoor stability of their devices remains elusive. A comprehensive operational outdoor study paired with photo- and thermo-induced degradation has yet to be documented.

In this study, we examine the stability of various Y-NFAs when paired with a common polymer donor, and vice versa. For Y-NFAs, we establish a connection between the molecular structure, specifically the end-group and side-chain, and their photostability. Through the combination of density functional theory (DFT) calculations on the energy barrier of photoisomerization and the analysis of device photostability, we have discovered that suppressing light-induced vinyl rotation can significantly improve the lifetime of the devices. Shifting our focus to polymer donors, we delve into the significance of various building blocks in determining the device lifetime. In order to evaluate the potential occurrence of side-chain breakage, we introduce a molecular descriptor for predicting the photostability of polymer donors and validate its effectiveness by testing it on 28 different polymeric materials. Under illumination, the chemical changes occurring in both Y-NFAs and polymer donors result in a noticeable increase in trap-assisted recombination, leading to a degradation in device performance when exposed to outdoor conditions. Furthermore, we conduct a systematic comparison of the photostability, thermostability, and outdoor stability of devices based on state-of-the-art materials. This comprehensive analysis enables us to gain a thorough understanding of how the photoactive layers impact the long-term performance, particularly in the hot and sunny climate of Saudi Arabia. Our findings provide valuable insights into the design and synthesis of photoactive materials, with the goal of attaining high efficiency and long-term stability in OSCs for outdoor applications.