In a groundbreaking advancement for organic photovoltaics, a team of researchers has unveiled a novel approach to elevating the efficiency and performance of organic solar cells by precisely controlling the crystallization dynamics of non-fullerene acceptors. Utilizing a crystallization-regulating additive called acenaphthene, they have demonstrated a transformative two-step crystallization process that significantly refines the molecular packing and orientation of acceptor materials within the active layer. This breakthrough paves the way for organic solar cells that break previous efficiency barriers, reaching certified power conversion efficiencies exceeding 20%, with fill factors peaking at a remarkable 83.2%.
Organic solar cells have long been heralded for their potential as low-cost, flexible, and lightweight energy-harvesting devices. However, their commercial viability hinged critically on overcoming persistent challenges, chief among them being the optimization of the nanoscale morphology and charge transport pathways within the photoactive layers. Central to this optimization is the molecular arrangement of donor and acceptor materials, which dictates the efficiency of exciton dissociation, charge transport, and ultimately, the photovoltaic performance. Traditionally, controlling these molecular assemblies has been a painstaking process, hampered by the complex crystallization dynamics inherent to organic semiconductors.
The innovative strategy introduced by Fu, Li, Liu, and colleagues addresses these complexities head-on by introducing acenaphthene—a crystallization-regulating agent that disrupts conventional crystallization kinetics in a manner conducive to ordered self-assembly. This additive orchestrates a two-step crystallization mechanism, marking a pivotal evolution from prior methodologies. Initially, acenaphthene instigates the formation of precise packing motifs among non-fullerene acceptor molecules, effectively “freezing” their arrangement at an optimal configuration. Subsequently, it methodically refines this crystalline framework, enhancing molecular orientation and promoting long-range order.
This stepwise modulation of the crystallization process engenders a morphology distinguished by its high degree of acceptor molecule orientation and crystallinity. Such molecular order is critically important because it establishes multiple charge-transport pathways within the active layer, which facilitate more efficient extraction of photogenerated charges. By constructing a conducive network for hole and electron transport, the material overcomes key limitations such as charge recombination and poor mobility—factors that have historically limited the fill factor and overall power conversion efficiency (PCE) in organic photovoltaics.
The practical outcome of this refined morphology manifests in extraordinary photovoltaic metrics. The researchers fabricated binary organic solar cells composed of donor-acceptor pairs, specifically D18 paired with L8-BO and PM1 paired with L8-BO-X. Both device configurations demonstrated unprecedented efficiencies, with the D18/L8-BO system achieving 20.9% efficiency (certified 20.4%) and the PM1/L8-BO-X design pushing even further to an impressive 21% (certified 20.5%). Equally noteworthy is the fill factor of 83.2% (certified 82.2%), which compares favorably to conventional inorganic systems and represents a new apex for organic solar cells.
The central innovation of acenaphthene’s role calls for deeper reflection on its molecular interactions. As a crystallization-regulating agent, it serves not merely as a passive additive but as a molecular director that tempers the nucleation and growth stages of acceptor crystallization. Its presence modulates intermolecular forces and kinetic pathways, encouraging the formation of stable and uniform crystalline domains. These domains act as conduits for charge transport, minimizing energetic disorder and facilitating faster charge extraction. This subtly conditioned self-assembly process is critical because it enables the active layer to maintain structural integrity and performance over time, addressing concerns linked to device stability.
In addition to boosting efficiency and fill factor, the two-step crystallization mechanism also impacts the morphological stability of the active layer. The fine-tuning of crystallinity and domain orientation translates into improved film robustness against thermal and mechanical stresses—a vital attribute for the commercial scalability and operational longevity of organic solar cells. The precise control over microstructural features afforded by acenaphthene addition therefore carries promising implications for device reliability and lifespan under real-world conditions.
From a broader perspective, this research underscores the importance of molecular-scale engineering within organic electronic devices. The interfacial and internal microstructures of photoactive layers have long been recognized as crucial performance determinants, but developing tools to manipulate these structures reliably remains a bottleneck. The strategy of employing tailored crystallization regulators to influence molecular packing unlocks a new design paradigm, whereby the energetics and kinetics of self-assembly can be engineered to amplify desired material properties.
The broader scientific community will likely see significant interest in expanding this approach to diverse donor-acceptor combinations beyond those investigated here. The modularity of molecular additives like acenaphthene offers a versatile platform to tune crystallization parameters across different non-fullerene acceptors, potentially leading to even greater device efficiencies or novel functionalities such as semi-transparency or enhanced mechanical flexibility. Parallel efforts could also investigate synergistic interactions with processing techniques like solvent annealing, thermal treatment, or additive blends to further elevate morphology and device metrics.
Furthermore, the high fill factors reported in this work challenge previous assumptions about the limits of organic photovoltaic performance. Achieving fill factors over 80% indicates a level of internal charge collection and recombination suppression that rivals many traditional silicon and perovskite solar cells. This parity establishes organic solar cells as practical contenders not only for niche applications requiring flexibility or low weight but also for mainstream power generation markets, especially where material cost and fabrication simplicity drive decision-making.
Environmental and economic implications are also compelling. Organic solar cells have often been touted as a sustainable alternative owing to their potential for roll-to-roll manufacturing and the absence of rare or toxic elements. Enhancing their efficiency to the 20+% range brings their energy payback times and lifecycle emissions into favorable territory, strengthening their candidacy as genuinely green energy solutions. As efforts intensify to decarbonize energy systems worldwide, advances such as those enabled by acenaphthene’s crystallization modulation will be crucial for integrating affordable, efficient, and scalable photovoltaic technologies.
This work additionally exemplifies how meticulous material design and fundamental understanding of crystallization kinetics can manifest in transformative device outcomes. It emphasizes that breakthroughs in functional organic materials require not only synthesis of novel molecules but also precise control over their organization at the nano- and mesoscale. The two-step crystallization process acts as a fine sculptor, bringing order to molecular chaos and unlocking the full potential of non-fullerene acceptors.
In sum, the application of acenaphthene to regulate the crystallization of acceptor molecules represents a paradigm shift in the fabrication of organic solar cells. By leveraging a meticulously engineered two-step crystallization process, these researchers have realized record-breaking efficiencies and fill factors that advance organic photovoltaics closer to widespread implementation. This illustrates the profound impact that controlling nanoscale morphology has on device physics and lays a compelling blueprint for future innovations in organic semiconductor technologies.
As the industry and academia continue to explore the frontiers of organic electronics, the importance of blending chemical ingenuity with advanced processing techniques becomes ever clearer. This pioneering research not only marks a milestone benchmark in device performance but also expands the toolkit available to scientists striving to push the boundaries of what organic solar cells can achieve. The efficient pathway carved by acenaphthene-modulated crystallization promises to accelerate the transition from lab-scale curiosities to commercially viable, high-performance energy solutions.
Looking ahead, the challenge will be to integrate these high-efficiency systems into scalable manufacturing processes without compromising their meticulously engineered morphologies. Addressing issues such as long-term stability under operational conditions, mechanical resilience in flexible formats, and compatibility with large-area printing methods will be essential for translating this scientific triumph into practical impact. However, given the magnitude of the current advances in device efficiency and fill factor, optimism remains high that such organic solar cells will soon become a significant contributor to the global renewable energy landscape.
The elegant interplay of crystallization kinetics and molecular self-assembly demonstrated here highlights the power of bottom-up design principles in materials science. As crystalline order is harnessed and manipulated, the efficiency bottlenecks that have long constrained organic photovoltaics begin to dissolve. This study stands as a testament to the relentless progress achievable through detailed understanding and control of molecular phenomena, heralding a new chapter for organic solar energy technology.
Subject of Research: Organic solar cells; crystallization dynamics of non-fullerene acceptors; organic photovoltaic efficiency.
Article Title: Two-step crystallization modulated through acenaphthene enabling 21% binary organic solar cells and 83.2% fill factor.
Article References:
Fu, J., Li, H., Liu, H. et al. Two-step crystallization modulated through acenaphthene enabling 21% binary organic solar cells and 83.2% fill factor. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01862-1
Image Credits: AI Generated
