Engineering topics
Publications and source records attributed to Li, Zhengke.
Two strong electron-donating moieties were fused into the molecular backbone of small molecular acceptors showing dramatically extended absorption beyond 900 nm.
Abstract For oligothiophene‐based donor polymers, changing the number of thiophene rings in each repeating unit is a simple and effective approach to tune their optical and electronic properties. While bithiophene‐, terthiophene‐, and quaterthiophene‐based polymers have been widely known and studied, pentathiophene‐based ones are rarely reported. Here, the pentathiophene‐based polymer PT5T, which yields extremely poor device performance with an efficiency of only 0.37%, is synthesized. However, after the introduction of two fluorine atoms to the center thiophene unit, the resulting polymer (PT5T‐2F) yields dramatic improvement in device performance with the fill factor and the power conversion efficiency improved to 70.8% and 9.69%, respectively. The morphological study shows that the difluorinated pentathiophene building block introduces enhanced molecular aggregation and crystallinity of PT5T‐2F, which facilitates the formation of bulk heterojunction blends with higher domain purity. Most importantly, despite its high crystallinity, PT5T‐2F can still produce reasonably small domain sizes in the polymer‐based blend. The results indicate that the difluorinated pentathiophene is a promising building block to construct donor polymers for nonfullerene organic solar cells.
Abstract The effects of alkyl chain regiochemistry on the properties of donor polymers and performances of non‐fullerene organic solar cells are investigated. Two donor polymers (PfBTAZ and PfBTAZS) are compared that have nearly identical chemical structures except for the regiochemistry of alkyl chains. The optical properties and crystallinity of two polymers are nearly identical yet the PfBTAZ:O‐IDTBR blend exhibits nearly double domain size compared to the blend based on PfBTAZS:O‐IDTBR. To reveal the origins of the very different domain size of two blends, the morphology of neat polymer films is characterized, and it is found that PfBTAZ tends to aggregate into much larger polymer fibers without the presence of O‐IDTBR. This indicates that it is not the polymer:O‐IDTBR interactions but the intrinsic aggregation properties of two polymers that determine the morphology features of neat and blend films. The stronger aggregation tendency of PfBTAZ could be explained by its more co‐planar geometry of the polymer backbone arising from the different alkyl chain regiochemistry. Combined with the similar trend observed in another set of donor polymers (PTFB‐P and PTFB‐PS), the results provide an important understanding of the structure–property relationships that could guide the development of donor polymers for non‐fullerene organic solar cells.