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. 2025 Jun 13;11(24):eadt6024.
doi: 10.1126/sciadv.adt6024. Epub 2025 Jun 13.

Enhancing singlet excitons delocalization via selective asymmetric fluorination of electron acceptors for efficient organic solar cells

Renjie Xu  1   2 , Yuanyuan Jiang  1   2 , Houyou Lei  3 , Feng Liu  1   3 , Kerui Liu  1   2 , Liheng Feng  3 , Guangliu Ran  4 , Wenkai Zhang  4 , Cheng Zhong  5 , Xiaozhang Zhu  1   2
Affiliations

Enhancing singlet excitons delocalization via selective asymmetric fluorination of electron acceptors for efficient organic solar cells

Renjie Xu et al. Sci Adv. .

Abstract

Exciton dissociation in organic solar cells (OSCs) is primarily achieved through interfacial charge-transfer (CT) states, leading to a trade-off between open-circuit voltage (VOC) and short-circuit current (JSC). Spatially dispersed delocalized singlet excitons (DSEs) in nonfullerene acceptors (NFAs) provide an alternative channel to promote charge generation without interfacial CT state. Here, we manipulate intermolecular interactions, carrier dynamics, and photovoltaic properties through selective asymmetric fluorination. Two asymmetric molecules, Z12 and Z13, were synthesized by substituting the terminal group with different fluorine atoms compared with the symmetrical molecule, Z11. Z12 showed enhanced molecular interactions, promoting to more compact and ordered stacking, which in turn promotes the DSE formation, benefiting the synergistic enhancement of VOC and JSC. The D18:Z12-based device achieved a remarkable power conversion efficiency of 19.5%, notably outperforming the other two devices. Our study indicates that controlling the molecular configuration by selective fluorination to enhance the DSE formation in NFAs is an effective strategy to achieve efficient OSCs.

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Figures

Fig. 1.
Fig. 1.. Structure and properties of materials.
(A) Chemical structure of Z11, Z12, and Z13. (B) UV-vis–NIR absorption spectra (film) and molar absorption coefficient (chloroform solution). (C) Energy diagram of D18, Z11, Z12, and Z13 thin films. (D) GIWAXS 1D line cuts of Z11, Z12, and Z13 neat films (the solid line is the OOP direction, and the dashed line is the IP direction).
Fig. 2.
Fig. 2.. Molecular dynamics simulations and femtosecond transient measurement.
(A) Statistics of the count of atoms involved in each instance of terminal group stacking in the three neat films. (B) Ratio of the count of atoms involved in each instance of terminal group stacking. (C) Complexation energy of different terminal groups (IC-XF/YF refers to the interaction between IC-XF and the IC-YF terminal group). (D to F) TA dynamics of GSB/ESA signals probed at ~820 nm and ~1580 nm in three neat films.
Fig. 3.
Fig. 3.. Photovoltaic performance and energy loss analysis.
(A) Characteristic J-V curves of D18:Z11, D18:Z12, and D18:Z13. (B) Corresponding EQE curves based on the D18:Z11, D18:Z12, and D18:Z13 devices. (C) Parameter comparison of the three OSCs. (D) EQEEL curves of the optimal devices. (E) Detailed energy loss for three OSCs. (F) Summary of PCEs and nonradiative energy loss for binary OSCs from the literature (see table S9) and this work.
Fig. 4.
Fig. 4.. Analysis of charge dynamics.
(A and B) Correlation between JSC/VOC and light intensity in the optimized three devices. (C) TPC curves for the two devices. (D) Charge density versus VOC. Carrier lifetime (E) and recombination rate coefficient (F) as a function of charge density of the devices. (G to I) Femtosecond transient absorption spectra of D18:Z11, D18:Z12, and D18:Z13 blend films.
Fig. 5.
Fig. 5.. Film morphology analysis.
(A) AFM height and phase images of the optimized D18:Z11, D18:Z12, and D18:Z13 blend films. (B) TEM images of D18:Z11, D18:Z12, and D18:Z13 blend films. (C) 2D GIWAXs patterns for the D18:Z11, D18:Z12, and D18:Z13 blends and (D) and corresponding 1D line cuts (the solid line is the OOP direction, and the dashed line is the IP direction). (E) Detailed parameters of GIWAXS profiles along with the OOP and IP direction. (F) Electron mobilities (μes) and hole mobilities (μhs) for the all devices. a.u., arbitrary unit.
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