Insulating Polymer Mediated Stability and Photovoltaic Performance of Organic Solar Cells: Influence of Molecular Weight

Abstract Insulating polymers are promising components for constructing high performance organic solar cells (OSCs) due to their advantages including low cost, excellent mechanical properties, and feasibility in morphology modulation. However, few studies have been conducted on the effect of molecular weight of insulating polymers on the performance of the corresponding OSCs. In this work, polymethyl methacrylate (PMMA) with different molecular weight (named as PMMA L and PMMA H ) are incorporated into a range of polymer:nonfullerene photovoltaic systems. It is found that although both PMMA L and PMMA H can suppress the energetic disorder and the nonradiative energy loss, and lead to enhanced open‐circuit voltage in their corresponding OSCs, distinct mechanical property, operational stability as well as photovoltaic performance are observed. PMMA L can modulate the molecular packing of the host components more effectively due to its superior chain segment mobility during the film‐forming process, which can drive the host components to form more ordered molecular packing and therefore superior photovoltaic performance. On the other hand, due to the better miscibility of PMMA H with the host system, especially the C5‐16 acceptor, PMMA H can be well dispersed in the host and form a stable framework that provides superior mechanical properties and operational stability.