Abstract:
Recently, the research team led by Jianhui Hou from the Institute of Chemistry, Chinese Academy of Sciences, reduced energy disorder through molecular design and reported a novel nonfullerene acceptor material, resulting in organic solar cells with outstanding photoelectric conversion efficiency. Researchers replaced the diphenyl cyclopentadiene on IT-4F with a triisopropylbenzene-modified pyrrole group to design and synthesize the TBB acceptor. The study showed that TBB exhibited significantly reduced energy disorder (23.2 vs. 32.7 meV), with a non-radiative energy loss of only 0.22 eV based on PBQx-TF:TBB cells, achieving a photoelectric conversion efficiency of 16.2%, one of the highest values among non-Y6 series. This work demonstrates that reducing energy disorder through rational molecular design is an important approach to improving the efficiency of organic solar cells.
Background:
Organic solar cells (OSCs) integrate many advantages such as lightweight, flexibility, semi-transparency, and suitability for solution printing processes, promising broad application prospects in portable energy supply for various scenarios. In recent years, thanks to continuous innovation in donor-acceptor materials, OSCs have achieved sustained breakthroughs in photoelectric conversion efficiency (PCEs). However, compared to inorganic silicon and organic/inorganic hybrid perovskite materials, organic semiconductors have larger energy disorder, which is one of the main challenges limiting further efficiency improvement. Theoretically, the energy disorder of organic semiconductor materials stems from various factors, including weak intermolecular interactions, chemical defects, and conformational changes. Reducing energy disorder can enhance charge transport, reduce recombination, and thus suppress energy loss. However, currently, only a few acceptors like Y6 series demonstrate relatively low energy disorder, urging the development of corresponding molecular control strategies.、
Highlights of the Article:
With the support of the National Natural Science Foundation of China and the Chinese Academy of Sciences, the research team led by Jianhui Hou from the Institute of Chemistry, Chinese Academy of Sciences, designed a trapezoidal structure for the new nonfullerene acceptor TBB by replacing the sp3 hybridized carbon group of IT-4F with a triisopropylbenzene-modified pyrrole unit. The synthesis route of TBB is shown in Figure 1.
Figure 2 shows the TBB single crystal structure obtained by vapor phase diffusion, where the twisting angle between the acceptor end group and the core is 11.3°, and the distance between the oxygen atom and the outer thiophene sulfur atom is 2.64 Å, indicating strong intramolecular noncovalent interactions in TBB, which help maintain planarity. The π-π distance between the end groups is about 3.30 Å, one of the closest stacking distances among nonfullerene acceptors, positively affecting the suppression of energy disorder. From solution state to film state, TBB exhibits a redshift of 100 nm in the maximum UV-visible absorption peak, indicating the formation of a highly ordered stacking structure in the film state, which is also verified from crystallinity characterization.
As shown in Figure 3, the energy disorder of TBB is significantly reduced compared to IT-4F, with a Urbach energy (Eu) of only 23 meV (compared to 33 meV for IT-4F). In the device, the charge carrier mobility of PBQx-TF:TBB is doubled compared to PBQx-TF:IT-4F, and the electroluminescence efficiency increases from 4.0×10-6 to 1.6×10-4, with a significant decrease in defect density. Finally, the device based on PBQx-TF:TBB achieves a PCE of 16.2%, far surpassing the 11.5% of PBQx-TF:IT-4F, making it one of the highest reported values for OSCs prepared using non-Y6 acceptors.
Conclusion and Outlook:
In summary, this article improves the efficiency of organic solar cells by reducing energy disorder through rational molecular design. A new nonfullerene acceptor TBB was designed and synthesized by replacing the sp3 hybridized carbon group of IT-4F with a triisopropylbenzene-modified pyrrole unit. TBB exhibits lower energy disorder (23.2 vs. 32.7 meV) and significantly enhances the performance of the cells. Based on PBQx-TF:TBB cells, with a non-radiative energy loss of only 0.22 eV, a photoelectric conversion efficiency of 16.2% is achieved, one of the highest reported values for non-Y6 series. This work provides important molecular control strategies for developing more efficient organic solar cells. The related findings are published in the form of a Research Article in CCS Chemistry, with Zi Li, a postdoctoral fellow at the Institute of Chemistry, Chinese Academy of Sciences, as the first author, and Jianhui Hou, a researcher at the Institute of Chemistry, Chinese Academy of Sciences, and Huifeng Yao, a professor at Southeast University, as corresponding authors.
Article Details:
A New Nonfullerene Acceptor with Suppressed Energy Disorder for High-Efficiency Organic Solar Cells
Zi Li, Huifeng Yao*, Zhihao Chen, Wenxuan Wang, Yang Xiao, Jianqiu Wang, Junzhen Ren, Tao Zhang, Jiayao Li, and Jianhui Hou*
Cite this by DOI: 10.31635/ccschem.024.202303631
Article Link: https://doi.org/10.31635/ccschem.024.202303631