All-polymer solar cells (APSCs) are highly valued for their excellent light and thermal stability as well as their flexibility, making them a promising solution for next-generation flexible power systems. Thanks to recent advancements in non-fullerene acceptor materials, high-performance polysmall molecule acceptors have seen significant progress. However, the development of high-efficiency polymer donors remains relatively slow. Addressing how to design and synthesize novel polymer donor materials, while regulating the stacking and orientation of donor/acceptor molecules, is key to improving photovoltaic performance and advancing all-polymer organic solar cells.
Recently, a team from the Qingdao Institute of Bioenergy and Process Chemistry, under the leadership of Dr. Bao Xichang, has made notable strides in this area. They have successfully designed and synthesized new ultra-wide bandgap (Eopt = 2.24 eV) polymer donor materials by minimizing charge transfer states and quinone resonance effects within the donor's main framework (see Fig. 1). These materials exhibit a high extinction coefficient and an absorption spectrum that perfectly aligns with the peak solar radiation range. Furthermore, they demonstrate excellent compatibility with acceptor materials and robust intermolecular interactions. This research yielded APSCs with efficiencies of 15.3% and 17.1%, surpassing many current donor materials. These findings provide valuable insights into designing donor materials for all-polymer solar cells and have been published in *Advanced Functional Materials*.
Another challenge in APSCs lies in the poor phase separation and low mixing entropy caused by strong inter-chain entanglement in conjugated polymers, which hinders the optimization of active layer morphology and limits overall performance. To address this, the research team developed a well-miscible polymer donor capable of deeply penetrating donor/acceptor (D/A) domains. This approach optimizes molecular accumulation and phase separation in the active layer, leading to efficient exciton and carrier utilization. Their ternary APSC with a bulk heterojunction (BHJ) structure achieved an impressive efficiency of 17.64% and showed remarkable thick-film tolerance. The inclusion of the third component not only promotes the formation of mixed phases but also independently optimizes the orderly accumulation of D/A domains, creating ideal pseudo-plane heterojunction (PPHJ) active layers. The resulting ternary APSC with a PPHJ structure reached an efficiency of 17.94% and exhibited outstanding device stability. The use of compatible third components to induce ordered D/A accumulation holds immense potential for future high-performance APSCs. These findings have been published in *Energy & Environmental Science*.
This research was supported by the National Natural Science Foundation of China, the International Cooperation Project of the Ministry of Science and Technology, and the special funds of the Shandong Energy Research Institute.
(See Fig. 1 below for the new molecular strategy to construct efficient polymer donor materials, and Fig. 2 for the tripartite approach to optimize molecular aggregation in the absorbing layer.)
[Fig. 1] A novel molecular strategy to build efficient polymer donor materials
[Fig. 2] A tripartite approach to optimize molecular aggregation in the active layer
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