Understanding the Structure-Stability Relationship of Photovoltaic Materials for Outdoor Stable Organic Solar Cells
Han Xu a, Jianhua Han a b, Derya Baran a
a KAUST: King Abdullah University of Science and Technology, 4700 King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
b Julius-Maximilian University Würzburg, Am Hubland, Würzburg, 97074, Germany
Oral, Han Xu, presentation 089
Publication date: 6th February 2024

Organic solar cells (OSCs) have attracted considerable attention for potential commercial applications because of their light weight, mechanical flexibility, semitransparency, and large-area manufacturing properties. Recent advancements in Y-series non-fullerene acceptors (Y-NFAs) and polymer donors have significantly improved the power conversion efficiency of OSCs. In light of these rapid efficiency improvements, it is essential to focus on the stability of photovoltaic materials. These materials are pivotal in determining the operational lifetime of OSCs under real-world conditions, ensuring they meet the necessary standards for future commercial viability. However, the relationship between the molecular structure and the outdoor stability of these devices remains unclear, and there is a deficiency in comprehensive studies that examine operational performance in combination with measurements of photostability and thermal stability.

Here, we explore the stability of various Y-NFAs alongside a common polymer donor and vice versa. Regarding Y-NFAs, we establish a connection between the molecular structure, specifically the endgroup and side-chain, and their photostability. Employing density functional theory (DFT) calculations on the energy barrier for photoisomerization, coupled with device photostability outcomes, we discern that inhibiting light-induced vinyl rotation effectively prolongs device lifetime. Shifting focus to polymer donors, we examine the significance of different building blocks in dictating device longevity. We propose a molecular descriptor to assess the possibility of side-chain breakage. The chemical alterations undergone by Y-NFAs and polymer donors under illumination ultimately lead to notably enhanced trap-assisted recombination, thus compromising device performance in outdoor conditions. Furthermore, we systematically compare the photostability, thermostability, and outdoor stability of devices based on state-of-the-art materials to obtain a comprehensive understanding of how the photoactive layers influence long-term performance in the hot and sunny climate of Saudi Arabia. Our findings offer valuable insights into designing and synthesizing photoactive materials with the goal of achieving high efficiency and long-term stability in outdoor organic solar cells (OSCs).

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