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Nature Photonics (2026)
The development of high-performance perovskite–organic tandem solar cells has been impeded by the scarcity of efficient narrow-bandgap small-molecule acceptors. Realizing such materials requires overcoming the energy gap law to minimize the energy loss and simultaneously optimizing the donor–acceptor phase separation. Here, to address these challenges, we present an asymmetric halogen heavy-atom modification strategy, synthesizing a series of narrow-bandgap small-molecule acceptors, namely, E3-2Cl, E3-2Br and E3-2I. The heavy-atom effect restricts molecular backbone vibrations and suppresses reorganization energy, thereby enhancing the luminescence efficiency and reducing the non-radiative energy loss, which collectively contribute to a higher open-circuit voltage. In parallel, this approach strengthens terminal-mediated intermolecular interactions, leading to well-defined donor–acceptor double fibril morphology and improved phase separation in the blend films. As a result, the organic solar cells based on E3-2Cl deliver a remarkably low energy loss of 0.488 eV and a power conversion efficiency of 20.7%, ranking among the highest for low-energy-loss organic solar cells. Furthermore, by integrating the E3-2Cl-based organic rear sub-cell with a wide-bandgap perovskite front cell, we demonstrate a perovskite–organic tandem solar cell with an open-circuit voltage of 2.18 V and a power conversion efficiency of 28.2% (certified, 27.5%) under an aperture area exceeding 1 cm2. This work establishes a viable molecular design strategy for developing low-energy-loss narrow-bandgap acceptors, paving the way for high-efficiency perovskite–organic tandem solar cells.
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The data supporting the findings of this study are available within the article and its Supplementary Information. Additional data are available from the corresponding author on request. Source data are provided with this paper.
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This work was supported by the Beijing Nova Program (number 20240484597, X.L.), the National Natural Science Foundation of China (number 52203248, X.L.), the Strategic Priority Research Program of the Chinese Academy of Sciences (number XDB0520102, Yongfang Li) and the National Key Research and Development Program of China (number 2024YFB4205200, L.M.). H.H. thanks Shenzhen HUASUAN Technology Co., Ltd for assistance with the MD calculations. H.H. thanks X. Jiang and G. Sun for their kind help and advice.
These authors contributed equally: Haozhe He, Zhenrong Jia.
CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
Haozhe He, Xiaojun Li, Shucheng Qin, Jinyuan Zhang, Yuechen Li, Kaige Yin, Yiyang Wang, Zekun Chen, Lei Meng & Yongfang Li
School of Chemical Science, University of Chinese Academy of Sciences, Beijing, China
Haozhe He, Xiaojun Li, Shucheng Qin, Yuechen Li, Kaige Yin, Yiyang Wang, Zekun Chen, Lei Meng & Yongfang Li
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore
Zhenrong Jia & Yi Hou
State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, China
Ke Wang, Zhaozhao Bi & Wei Ma
Laboratory of Advanced Optoelectronic Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, China
Yongfang Li
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X.L. conceived the study, designed the experiments and directed this project. H.H. designed and synthesized the asymmetric SMAs, and fabricated and characterized the single-junction OSCs. Z.J. optimized and characterized the perovskite–organic TSCs. S.Q. conducted the density functional theory theoretical calculations. Yuechen Li and Z.C. participated in the optimization of device fabrication. K.Y. contributed to the energy loss measurements. J.Z. conducted the TA measurements and data analysis. Y.W. contributed to the scanning electron microscopy tests. K.W., Z.B. and W.M. carried out the GIWAXS measurements and assisted with data analysis. X.L., Yongfang Li and Y.H. supervised the project. H.H., Z.J., X.L., Yongfang Li and Y.H. wrote the paper. All authors participated in the data analysis and commented on the paper.
Correspondence to Xiaojun Li, Yi Hou or Yongfang Li.
The authors declare no competing interests.
Nature Photonics thanks Shangfeng Yang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Figs. 1–55, Tables 1–11, Notes 1–6, Methods and References.
Molecular vibrational diagrams at a frequency of around 1,578 cm−1.
Molecular vibrational diagrams at a frequency of around 1,563 cm−1.
Molecular vibrational diagrams at a frequency of around 1,608 cm−1.
Molecular vibrational diagrams at a frequency of around 1,368 cm−1.
Source data for Supplementary Figs. 14–16, 34, 51, 53 and 54.
Source data for Figs. 1–4.
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He, H., Jia, Z., Li, X. et al. Narrow-bandgap acceptors with suppressed exciton thermalization loss for highly efficient perovskite–organic tandem solar cells. Nat. Photon. (2026). https://doi.org/10.1038/s41566-026-01906-2
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