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DOE OSTI · 2556793

Fluorinated polythiophenes with ester side chains for boosting the V OC and efficiency in non-fullerene polymer solar cells

Su, Li-Yun [Southern Taiwan University Science and Technology, Tainan (Taiwan); National Taiwan University, Taipei (Taiwan)] (ORCID:0000000291692457)·Zhou, Yi-Ling [National Taiwan University, Taipei (Taiwan)]·Chen, Yu-Ting [National Taiwan University, Taipei (Taiwan)]·Chen, Guan-Lin [National Taiwan University, Taipei (Taiwan)]·Tseng, Kai-Wei [National Taiwan University, Taipei (Taiwan)]·Tukachev, Nikita [University of Glasgow, Scotland (United Kingdom)] (ORCID:000000022647447X)·Zhugayevych, Andriy [Max Planck Institute for Polymer Research, Mainz (Germany)] (ORCID:0000000347131289)·Tretiak, Sergei [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States). Center for Integrated Nanotechnologies (CINT)]·Wang, Leeyih [National Taiwan University, Taipei (Taiwan)] (ORCID:0000000263680141)
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Abstract

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approximates the 19 % threshold, wide bandgap (WBG) polythiophenes (PTs) have gained increasing attention due to their simple chemical structures and ease of synthesis, making them promising candidates for large-scale production. However, the benchmark polymer poly(3-hexylthiophene) (P3HT) is limited by its high-lying HOMO energy level, which restricts the open-circuit voltage (V OC ) in solar cells. Here, in this study, we introduce a novel series of PT derivatives (PDC8-T, PDC8-3T, PDC16-3T, and PDC16-3T-2F) featuring ester side chains designed to fine-tune electronic properties through a streamlined three-step synthesis. Additionally, we incorporated a π-spacer to reduce steric hindrance and elongated alkyl side chains to improve solubility and processability. Compared to P3HT, these PT derivatives demonstrate a significant reduction in HOMO energy levels, lowering by approximately 0.3–0.4 eV. Among them, PDC16-3T-2F—with fluorine atom substitution—achieves the lowest HOMO energy level, induces a coplanar molecular conformation, and enhances polymer aggregation behavior. We evaluated these PT derivatives in inverted non-fullerene bulk-heterojunction (NFA BHJ) OPVs. The PDC8-3T device showed a relatively low PCE of 0.69 %, with a V OC of 0.76 V, a short-circuit current density (J SC ) of 3.32 mA/cm 2 , and a fill factor (FF) of 27.3 %. In contrast, the PDC16-3T-2F device achieved an impressive PCE of 7.21 %, with a V OC of 0.85 V, a J SC of 14.60 mA/cm 2 , and an FF of 58.4 %. This remarkable improvement is attributed to the fluorine substitution, which not only enhances molecular orientation but also downshifts the HOMO energy level and further boosts the V OC . Hence, these molecular design strategies have led to a fibrillar bicontinuous interpenetrating network with optimal nanoscale phase separation within the active layer.

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14 SOLAR ENERGYEster side group-based polythiopheneFluorinationMaterial ScienceNon-fullerene polymer solar cells

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Su, Li-Yun [Southern Taiwan University Science and Technology, Tainan (Taiwan); National Taiwan University, Taipei (Taiwan)] (ORCID:0000000291692457), Zhou, Yi-Ling [National Taiwan University, Taipei (Taiwan)], Chen, Yu-Ting [National Taiwan University, Taipei (Taiwan)], Chen, Guan-Lin [National Taiwan University, Taipei (Taiwan)], Tseng, Kai-Wei [National Taiwan University, Taipei (Taiwan)], Tukachev, Nikita [University of Glasgow, Scotland (United Kingdom)] (ORCID:000000022647447X), Zhugayevych, Andriy [Max Planck Institute for Polymer Research, Mainz (Germany)] (ORCID:0000000347131289), Tretiak, Sergei [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States). Center for Integrated Nanotechnologies (CINT)], Wang, Leeyih [National Taiwan University, Taipei (Taiwan)] (ORCID:0000000263680141). 2025-03-31. Fluorinated polythiophenes with ester side chains for boosting the V OC and efficiency in non-fullerene polymer solar cells. https://doi.org/10.1016/j.polymer.2025.128336

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