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Non-covalent "conformational lock" isomerization for high-performance all-small-molecule organic solar cells

Introduction


       In recent years, non-covalent "conformational locks" (NoCLs) have been regarded as an important strategy for designing high-performance organic/polymer semiconductor materials. On the one hand, the introduction of non-covalent "conformational locks" such as S·O, S·F, S·N into semiconductor materials can significantly improve the rigidity and planarity of the skeleton and reduce the recombination energy, thereby It is beneficial to improve the charge transport properties of materials and the performance of devices. On the other hand, the introduction of the non-covalent "conformational lock" strategy can usually reduce the complexity and difficulty of synthesis, reduce the cost of synthesis, and is conducive to the industrialization of materials. Therefore, the research group of Professor Huang Hui from the University of Chinese Academy of Sciences has tried to apply this strategy to the exploration of low-cost, high-performance electron acceptor materials in recent years, and has achieved a series of important scientific research results (Sci. China Chem. 2021, 64, 228-231; Angew. Chem. Int. Ed. 2021, 60, 12475-12481; Angew. Chem. Int. Ed. 2021, 60, 17720-17725; Adv. Funct. Mater. 2022, 32, 2108861) . However, this strategy has received little attention in the design of small molecule donor materials. Recently, Professor Huang Hui's research group from the University of Chinese Academy of Sciences has made new breakthroughs in this research field, and the related results were published in Adv. Funct. Mater. 2022, 2112433 (DOI: 10.1002/adfm.202112433).


Cutting-edge scientific research achievements


Non-covalent "conformational lock" isomerization for high-performance all-small-molecule organic solar cells


       In recent years, high-performance organic solar cells have been realized mainly based on wide-bandgap polymer donor materials. However, batch-to-batch variability is common in polymer materials, which poses a significant obstacle to device reproducibility. Therefore, it is particularly important to develop high-performance small-molecule donor materials with defined molecular weights and easy purification. In the early stage, Professor Huang Hui's research group successfully applied the non-covalent "conformational lock" strategy to the development of low-cost, high-performance electron acceptor materials. Based on this work, the authors synthesized a pair of regioisomeric small molecule donor materials BT-O1 and BT-O2 by introducing a non-covalent "conformational lock" strategy (Fig. 1). Theoretical results show that due to the introduction of S·O non-covalent "conformational locks", both small-molecule materials have planar backbones and small internal reorganization energies.

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Figure 1. Schematic diagram of the chemical structure and photoelectric and solid-state packing behavior of small molecule donors isomerized by non-covalent "conformational lock"


(Source: Adv. Funct. Mater.)

 

     The authors further studied and found that the regioisomerization of the non-covalent "conformational lock" has a great influence on the light absorption ability, energy level, and solid-state packing behavior of the two materials (Fig. 1). Therefore, the BT-O2-based device exhibited an energy conversion efficiency of 13.99% when organic solar cell devices were prepared using H3 as an acceptor material blend (Fig. 2). This result is far superior to the BT-O1-based device performance (4.07%).

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Figure 2. Schematic diagram of photovoltaic device research, recombination mechanism, and energy loss


(Source: Adv. Funct. Mater.)

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Figure 3. Schematic diagram of the hybrid film morphology study


(Source: Adv. Funct. Mater.)

 

       作者继而通过研究电荷复合损失、激子解离效率、能量损失及混合膜形貌,揭示了上述两个器件在性能上具有明显差异的原因(图2和图3)。

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Figure 4. Schematic diagram of three-component photovoltaic performance and third-party verification results


(Source: Adv. Funct. Mater.)

       

Finally, the authors prepared a ternary blend system by adding a small amount of fullerene derivative PC71BM to the BT-O2:H3 system, and obtained a device performance of 15.34% (the efficiency verified by the Chinese Academy of Metrology is 14.6%) (Figure 4).


Summarize:


       The authors effectively regulated the optoelectronic properties, solid-state stacking behavior and photovoltaic device performance of small molecule acceptors through the strategy of non-covalent "conformational lock" regioisomerism, which pointed out a new idea for the exploration of high-performance small molecule donor materials.


      This achievement was published on Adv. Funct. Mater. (Adv. Funct. Mater. 2022, 2112433) under the title "High-Performance All-Small-Molecule Organic Solar Cells Enabled by Regio-Isomerization of Noncovalently Conformational Locks". The first author is Associate Professor Zhang Xin from the University of Chinese Academy of Sciences, and Qin Linqing from the University of Chinese Academy of Sciences, Li Yuhao from the Chinese University of Hong Kong, and Yu Jianwei from Lin Xueping University are the co-first authors. The corresponding authors are Associate Professor Zhang Xin and Professor Huang Hui from the University of Chinese Academy of Sciences, and Professor Lu Xinhui from the Chinese University of Hong Kong. The above research work has been funded by the National Natural Science Foundation of China, the National Key Research and Development Program, and the Central Universities Fundamental Research Fund.

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