On the Stability of Non‐fullerene Acceptors and Their Corresponding Organic Solar Cells: Influence of Side Chains

Abstract

Side chain engineering is a widely explored strategy in the molecular design for non-fullerene acceptors (NFAs). Although the relationship between side chain structures and optoelectronic properties of NFAs is well clarified, the effect of side chain structures on the stability of NFAs and their corresponding organic solar cells (OSCs) is rarely reported. Herein, a series of Y-family NFAs with varying side-chains are studied to investigate their degradation upon multiple stresses including water, oxygen from ambient, chemical environment from ZnO electron transport layer, temperature, and ultraviolet light. The results show that all of these Y-family NFAs are highly stable against water and oxygen in ambient dark condition, while their photochemical and thermal stabilities decrease with the increasing side chain length. NFAs with shorter side chains are not only more resistant to photooxidation and photocatalytic reactions, but also can hamper the formation of large phase-separated NFA domains upon storage in both glovebox and ambient conditions. As such, the PM6:NFA OSC with short side-chain NFA also exhibits superior operational stability, associating with a higher T 80 lifetime. This study demonstrates that the side chains must be considered to obtain stable OSCs.

Hybrid Cycloalkyl‐Alkyl Chain‐Based Symmetric/Asymmetric Acceptors with Optimized Crystal Packing and Interfacial Exciton Properties for Efficient Organic Solar Cells

“…Among them, the modification of the side chains, including the variation of size, topology (linear or branched), branching points, symmetry breaking, and dimension are the most commonly used approaches for precisely modulating the solubility, molecular crystallization, and packing behavior of SMAs. [52][53][54][55][56] For example, Yan et al demonstrated that different positions of alkyl-chain-branching can alter the molecular packing of SMAs and optimize the phase separation and exciton dissociation. [52] Moreover, by replacing the straight n-undecyl chain on Y6 with 2-butyloctyl, the molecular packing behavior can be changed completely and the structural order and charge transport in thin films can be improved, delivering significantly improved open-circuit voltage (V oc ) and fill factor (FF).…”

Correlation of Local Isomerization Induced Lateral and Terminal Torsions with Performance and Stability of Organic Photovoltaics

“…However, the structure modifications of NFAs also need to consider the effect on the long-term stability of the corresponding OPV devices, since the molecular planarity and aggregation behavior of NFAs are strongly related to the morphology evolution of relevant bulk hetero-junction (BHJ) under external stresses. − It is believed that the steric hinderance of alkyl chains has significant influence on the molecular backbone geometries, affecting the aggregation behavior of NFAs and the photovoltaic performance and stability of corresponding solar cell devices. − Therefore, it is possible to acquire a high-performance and stable solar cell simultaneously by introducing bulky conjugated side-groups on NFAs with subtly modified local structures.…”

Investigation of isomerization effects on the photovoltaic performance of fused-ring electron acceptors via side-chain position manipulation

“…13,14 Therefore, side chains play a crucial role in the photovoltaic performance of FREAs. In recent years, a variety of strategies, such as optimizing side-chain length, 15,16 adjusting side-chain structure, [17][18][19] changing aryl chains to alkyl chains, 20,21 and introducing highly dielectric chains, 22,23 have been employed to finely regulate the miscibility, improve the crystallinity and facilitate exciton dissociation of FREAs, thus enhancing the PCEs of OSCs. However, the position of side chains on the molecular backbone, which would impact the electronic structure, molecular packing and the miscibility of FREAs, has been rarely investigated so far.…”