Impact of pendent naphthalenedimide content in random double-cable conjugated polymers on their microstructures and photovoltaic performance

Double-cable conjugated polymers have shown promising application in single-component organic solar cells, in which the microstructures of donor/acceptor segments have a significant impact on their photovoltaic performance. Double-cable polymers always use alternating copolymers design, in which the pendent acceptor side units have the fixed content. If rationally tuning the pendent acceptor contents, it will allow observing the morphology evolution in these polymers, but these polymers have not yet been designed. In this work, we have developed a series of random double-cable conjugated polymers in which the content of pendent naphthalenediimide (NDI) could be easily tuned by changing the ratio of monomers. The physical, crystalline and photovoltaic properties of these polymers were systematically studied. The results revealed that when NDI contents were higher than 30%, NDI side units started to generate ordered nanostructures, which was helpful in enhancing the crystallinity of conjugated backbones. The morphology evolution was then strongly linked to the photovoltaic performance.