Effect of alkyl side chains of twisted conjugated polymer donors on photovoltaic performance

This is an exciting topic on maximizing the photovoltaic performance for a given conjugated skeleton by optimizing the side chains. In this work, we report two conjugated polymers (P3TCO-D and P3TCO-DMO) with the same conjugated backbone, the only difference in alkyl chains of carbonyl units (n-decyl and 3,7-dimethyloctyl). Both polymers have similar molecular weights, polydispersity indexes, and molecular energy levels. The P3TCOD has a stronger aggregation behavior than P3TCO-DMO. Interestingly, both pure polymer films have similar surface morphology. After blending with an electron acceptor of IT-4F, P3TCO-D: IT-4F film shows remarkable increased surface roughness of 23.2 nm and phase-separation. In contrast, 3TCO-DMO: IT-4F film displays slightly increased surface roughness of 3.82 nm and good phase-separation. In polymer solar cells, the P3TCO-D-based device gives a decent power conversion efficiency (PCE) of 10.1%, while the P3TCO-DMO-based device produces a better PCE of 12.8%. This work demonstrates that the optimization of side chains in the twisted conjugated polymers is very important to improve their photovoltaic performances.

Automated summary

Optimizing side chains can maximize the photovoltaic performance of conjugated polymers, influencing aggregation behavior and phase separation, leading to improved power conversion efficiency in polymer solar cells.