Recently, Professor Hongliang Zhong from the Center for Advanced Low Dimension Materials published a research paper titled “One pot synthesis of quasi block fluoropolymers for graded heterojunctions via dual resurfacing” in Nature Communications. This study reports a series of novel multi fluoropolymer materials. Through a synergistic “resurfacing” strategy driven by surface energy and fluorous solvents, the team successfully achieved an ideal graded heterojunction structure in organic solar cells (OSCs), delivering a device efficiency of 19.60%.
In organic solar cells, the donor/acceptor heterojunction structure is critical for exciton dissociation and charge transport. Although conventional bulk heterojunctions (BHJs) provide abundant donor–acceptor interfaces, they inevitably suffer from charge recombination losses. Graded heterojunctions (GHJs), which combine the short exciton diffusion distance of BHJs with the charge gradient of bilayer heterojunctions, have long faced challenges in solution processing.
To address this challenge, the research team designed and synthesized a series of multi fluoropolymers bearing heptafluoroisopropoxyl side chains. They found that the significantly different reactivities of fluorinated and conventional monomers enable the formation of a quasi block copolymer (qb PF20) in a one pot polymerization. The structure and performance of qb PF20 are comparable to those of a two step synthesized block copolymer (b PF20) and are markedly superior to those of a random copolymer (ra PF20). Owing to the ultra low surface energy of the fluorinated blocks, these fluoropolymers undergo “resurfacing” during solution casting – the fluorinated blocks spontaneously migrate to the film surface. When the active layer is prepared by sequential deposition, the small molecule acceptor solution is spin coated onto the underlying fluoropolymer film; the acceptor penetrates downward while the donor spontaneously moves upward, thereby generating a vertical donor/acceptor gradient distribution.
Figure 1 | The one pot synthesized quasi block fluoropolymer (qb PF20) exhibits performance rivaling that of a traditional two step synthesized block copolymer.
To further optimize the gradient distribution, the team innovatively introduced a “fluorous solvent vapor annealing (FSVA)” device engineering strategy. Leveraging the unique solubility of multi fluoropolymers in fluorous solvents, FSVA treatment induces the fluoropolymer to resurface again, achieving a secondary resurfacing and a more uniform graded heterojunction. The optimized qb PF20 based device achieves a power conversion efficiency of 19.60%, along with excellent batch to batch reproducibility and universality.
Figure 2 | Sequential deposition combined with FSVA treatment achieves an optimal graded heterojunction through dual resurfacing.
Ph.D. candidates Zhilong He and Siyuan Li from Professor Zhong’s group are the co first authors of the paper. Professor Hongliang Zhong is the sole corresponding author. Donghua University is the first corresponding institution. Professor Zheng Tang’s group at Donghua University, Professor Guanghao Lu’s group at Xi’an Jiaotong University, and Professors Chang Zhi Li and Lijian Zuo’s groups at Zhejiang University also made important contributions to this work. The research was supported by the National Natural Science Foundation of China, the Natural Science Foundation of Shanghai, the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University, and the start up research fund of Donghua University.
Link to the paper: https://doi.org/10.1038/s41467-026-71721-4
