Alcohol-Soluble Conjugated Polymers as Cathode Interlayers for All-Polymer Solar Cells

Conjugated polymers with polar side-chain components have successfully been used as cathode interfacial materials (CIMs) to improve the performances of polymer solar cells with fullerenes as acceptors. However, their uses and functions in all-polymer solar cells (all-PSCs) have not been well-investigated. Therefore, in this work, four conjugated polymers bearing different functional side chains, including dimethylamine, diethanolamine, and imidazole, were used as CIMs to study their effects on all-PSCs. With a combination of high-performing acceptor and donor polymers as active layers, the performances of the devices based on the four CIMs were compared with conventional devices with LiF/Al and Al as cathode. Compared to the devices with only Al as cathode, the devices comprising conjugated polymers as CIMs presented large improvement in power conversion efficiency from 2.7% to around 5.3%, which is comparable to the devices with LiF/Al as cathode. The encouraging results demonstrated that the use of conjugated interfacial polymers is a robust way to improve the performances of all-PSCs and can elegantly circumvent the use of low work function metals as cathodes. This is very important for roll-to-roll processing of flexible and large-scale solar cells.