Extension on the Conjugated Framework of Non-fullerene Electron Acceptors toward Highly Efficient Organic Photovoltaics

Abstract

Extending the π-conjugated framework of Non-fullerene electron acceptors (NFAs) have been considered as an effective method to improve the optoelectronic properties, however, how does the conjugation extension affect the molecular packing and aggregation behavior of NFAs and further determine the photovoltaic performance in their binary and ternary solar cells remain unclear. In this work, we find that extending the end-group of a cutting-edge NFA C5-16 with biphenyl moiety can enlarge the torsional angles and hamper the intermolecular interactions, whilst the extension of the quinoline moiety on the backbone core can encourage the core-to-core interactions, allowing prolonged crystallization period during the film-formation process and leading to reduced morphological and excitonic static disorder for acceptor. By further combining the end-group and core extended NFA C5Qx-B6F with C5-16, the C5Qx-B6F:C5-16 blend film not only retains improved structural order with reduced excitonic static disorder for acceptor like C5Qx-B6F, but also obtains molecular packing transformation from A-to-A and D-to-D to A-to-D, directing to an efficient charge collection ability with suppressed bimolecular recombination. As the results, a maximum PCE of 20.3%, FF of 81.8%, JSC of 27.6 mA cm-2 and VOC of 0.899 V are obtained, with elevated operational T80 lifetime due to improved morphological stability that benefits from less free volume in the photoactive film.