Elucidating the structure-function relationships of organic semiconductors has been central to the advancement of organic photovoltaics (OPVs). In particular, enhancing the performance of p-type materials in disordered heterojunctions is broadly acknowledged as the principal factor leading to current trends of improved power conversion efficiencies (PCEs). However, two additional factors are crucially important for the next step forward in improving PCEs. First, investigating the influence, design and synthesis of new n-type materials, specifically fullerene acceptors, is of high importance. Second, because fullerene performance is often compromised by the morphological disorder of bulk heterojunctions, developing fullerenes systems that retain fidelity within disordered blends is also of broad interest. In light of these challenges, the field has witnessed a notable shift towards developing a comprehensive understanding of the design rules needed to advance the performance of fullerene acceptors in bulk heterojunctions.

This work spotlights two multi-functional fullerene systems designed for blended heterojunctions. First, the synthesis of several novel fullerene-dye adducts with enhanced photon absorption will be presented. The ability of these adducts to absorb visible light in their pure state was evaluated and systematically examined versus their capacity to complement the absorption of low band gap donors and mediate charge transport in bulk heterojunctions. Second, mixed fullerene ternary blends were introduced as a strategy to stabilize the morphology in bulk heterojunctions and prolong operational lifetimes of OPV devices. Combined, these two systems offer unique insight into the rational design of fullerenes for their application in blended systems.