Quinoxaline Terpolymer-Controlled Miscibility With Oligomeric Acceptors for Over 20% Efficiency, Highly Stable and Stretchable Polymer Solar Cells.

Abstract

While the emergence of oligomeric acceptors has improved the operational stability of polymer solar cells (PSCs), power conversion efficiencies (PCEs) and mechanical properties remain morphology-limited, necessitating tailored polymer donors. Using tethered dimeric acceptor (DY2) as a model acceptor, we demonstrate how strategic modification of the classical D18 donor enhances miscibility and thus device performance. Specially, we developed a new quinoxaline (TQx) building block and incorporated it into D18 via random copolymerization, producing D18-TQxn terpolymers (n = 5, 10, 15) with 5%-15% TQx proportion. The polar moieties in TQx enhance the surface energy of the terpolymers (improving thermodynamic miscibility) while also modulating the backbone conformation of D18, thereby tuning the crystallization kinetics. The optimal D18-TQx10 exhibits optimized miscibility with DY2, achieving a remarkable PCE of 20.21%, among the highest reported for binary oligomeric acceptor based devices. Furthermore, the D18-TQx10 blend exhibits significantly enhanced stretchability, with a crack-onset strain nearly three times greater than that of the pristine D18-based device. It also demonstrates good compatibility with a range of dimeric acceptors. This work establishes a dual-control strategy using a quinoxaline terpolymer to regulate thermodynamic miscibility and crystallization kinetics, addressing the key challenges of morphology control for high performance PSCs using oligomeric acceptors.