Synthesis and characterization of NFA-based polymers for solar cells with improved thermal stability.

Among the latest advances in organic solar cells, all-polymer solar cells based on non-fullerene acceptors (NFAs) are emerging as a promising way to improve device stability. However, the synthesis of new electron-accepting polymers suitable for the active layer remains relatively unexplored. Current efforts primarily focus on maximizing photovoltaic conversion efficiency using PY-IT, a polymer derived from Y6. By contrast, there is a lack of fundamental research into controlling polymerization processes and the effect of the intrinsic optoelectronic properties of NFA-based polymers on their reactivity and stability when subjected to thermal stress and light soaking. To address this, we present the synthesis of a series of NFA-based polymers that incorporate thiophene, indacenodithiophene or a thienothiophene analogue. We systematically optimized Stille polymerisation by evaluating a range of phosphine ligands and correlating their performance with Tollman electronic and steric parameters, an approach that has rarely been explored in the literature. The resulting polymers exhibit improved macromolecular control, good solubility in