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Balanced Intra- and Interchain Exciton Delocalization Enables Efficient All-Polymer Solar Cells

Yu Guo1, Yuang Fu2, Xianzhao Liu1, Youcai Liang3, Fei Huang3, Xinhui Lu2, and Philip C.Y. Chow1,*

  • *Contact author: pcyc@hku.hk
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PRX Energy 5, 023008 – Published 8 June, 2026

DOI: https://doi.org/10.1103/fls9-jc34

Abstract

Polymerized Y-type nonfullerene acceptors (PY-NFAs) have shown great promise for efficient and stable organic solar cells (OSCs), yet their excited-state dynamics and structure-photophysics-performance relationships remain unclear. Here, we investigate a series of PY-NFAs and distinguish between intrachain excitons (intra-Ex) and interchain excitons (inter-Ex) formed in the solid state using cryogenic transient absorption (TA) spectroscopy at 100 K. We identify the emergence of trapped intra-Ex in the PY-NFA films from approximately 100 ps onwards after photoexcitation. By comparing this low-temperature TA signal among different PY-NFA films, we uncover a strong correlation between the trapped intra-Ex signature and the performance of these PY-NFAs in donor-acceptor blend OSC devices. This correlation indicates that the low-temperature TA response provides a quantitative measure of structural disorder in the PY-NFA aggregates and in the corresponding donor-acceptor blends. Correlating these spectroscopic results with molecular packing and morphological data, we reveal that high-performance PY-NFAs simultaneously exhibit (1) extended backbone conjugation and large intrachain exciton bandwidths and (2) uniform, oriented interchain packing despite moderately increased π-π stacking distances. These findings provide new design rules for PY-NFAs and offer deeper insight into how structural disorder and exciton dynamics govern OSC performance.

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Popular Summary

Organic solar cells (OSCs) are a promising renewable energy technology because they are inexpensive, flexible, and lightweight. A new class of polymerized electron-accepting materials (PY-NFAs) has recently enabled OSCs with high solar-to-electricity power conversion efficiencies and improved operational stability. However, it remains unclear how the materials' molecular structure and packing influence the properties of photoexcited electron-hole pairs (excitons) and OSC performance. In this work, using low-temperature spectroscopy, the authors identify trapped excitons in the disordered regions of PY-NFA aggregates, which provide a measure of structural disorder. Furthermore, the authors reveal that PY-NFAs with extended molecular backbones and oriented, slightly looser packing can achieve lower structural disorder and thus better device performance. This is in contrast with the conventional view that tighter molecular packing generally contributes to better OSC device performance. Therefore, this study provides new insights into the design and development of next-generation OSC materials.

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Outline

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PRX Energy 5, 023008– Published 8 June, 2026
  • Received 22 December 2025
  • Revised 9 April 2026
  • Accepted 4 May 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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