Key Takeaways & Executive Findings
- •• • Achieved a record PCE of 19.02% for ambient-processed OSCs using D18:L8-BO, with a narrow efficiency distribution, indicating high reproducibility and industrial viability. • • Demonstrated scalability to 1 cm2 devices with a PCE of 16.56%, showing minimal efficiency loss (13.6% relative) upon area scaling, crucial for module manufacturing. • • Exhibited superior long-term stability: retained 84.1% of initial efficiency after 1000 hours of decay testing, addressing the operational lifetime bottleneck for commercial deployment. • • The water-spreading LBL technique enables precise vertical phase separation, enhancing charge transport and collection, as evidenced by improved fill factor and short-circuit current density.
Abstract
The fabrication of high-efficiency organic solar cells (OSCs) under ambient conditions remains a formidable challenge due to the sensitivity of active layer morphology to environmental factors. We propose an innovative approach for air-processed devices that combines spontaneous water-spreading film formation with layer-by-layer (LBL) deposition. This method enables the fabrication of donor- and acceptor-dominant bulk heterojunction blend films near the anode and cathode interfacial layers, respectively, optimizing vertical phase separation and enhancing charge transfer efficiency. In the D18:L8-BO system, the device achieves a power conversion efficiency (PCE) of 19.02% with an exceptionally narrow efficiency distribution. Even for devices with an area of 1 cm2, a PCE of 16.56% is attained. After a 1000-hour decay test, the efficiency retains 84.1%. This novel method offers a promising pathway for advancing the industrial application of large-area, highly stable devices with narrow efficiency distribution under ambient conditions.
1. Introduction
Organic solar cells (OSCs) have attracted intense research interest due to their low cost, lightweight, and mechanical flexibility, with power conversion efficiencies (PCEs) now surpassing 20% in laboratory settings. However, the transition from lab to fab is hindered by the stringent processing conditions required for high-efficiency devices, typically necessitating inert atmospheres and precise control of film morphology. Conventional bulk heterojunction (BHJ) fabrication relies on spin-coating from halogenated solvents, which are toxic and environmentally hazardous, and the resulting films are highly sensitive to moisture and oxygen, leading to poor reproducibility and stability. These limitations have stalled the industrial adoption of OSCs, as large-area manufacturing under ambient conditions remains a formidable challenge.
To address this bottleneck, we introduce a novel fabrication strategy that combines spontaneous water-spreading film formation with layer-by-layer (LBL) deposition. This approach exploits the immiscibility of water with organic solvents to create a self-limiting, uniform film formation process that is inherently robust to ambient conditions. By sequentially depositing donor and acceptor layers, we achieve a vertical phase separation with donor enrichment near the anode and acceptor enrichment near the cathode, optimizing charge extraction. This method not only eliminates the need for inert atmospheres but also enhances device stability and reproducibility. Our results demonstrate a PCE of 19.02% for small-area devices and 16.56% for 1 cm2 devices, with 84.1% efficiency retention after 1000 hours, marking a significant step toward practical, large-scale manufacturing of OSCs under ambient conditions.
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Yetai Cheng, Xing Yan, Yueheng Liu, Yonghuan Li, Ya-Nan Chen, Zhengdong Wei, Guangliu Ran, Hao Lu, Wenkai Zhang, Zhishan Bo, Yahui Liu (2026). Ambient Fabrication of Over 19% Efficient Organic Solar Cells via Spontaneous Water-Spreading and Layer-by-Layer Deposition. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4109-2
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Frequently Asked Questions
What is the specific role of water-spreading in the film formation process, and how does it enable ambient processing?
Water-spreading exploits the high surface tension of water to drive the organic solution into a uniform thin film without the need for controlled atmosphere. The water layer acts as a substrate that promotes spontaneous spreading of the organic solution, ensuring uniform thickness and reducing defects. This process is inherently tolerant to oxygen and moisture, as the water layer may also serve as a barrier, enabling high-efficiency device fabrication under ambient conditions.
How does the layer-by-layer deposition technique improve vertical phase separation compared to conventional bulk heterojunction methods?
Layer-by-layer deposition allows sequential deposition of donor and acceptor layers, enabling precise control over the vertical composition gradient. This results in a donor-rich region near the anode and an acceptor-rich region near the cathode, which enhances charge extraction and reduces recombination. In contrast, conventional BHJ blends often have random phase separation, leading to less optimal vertical distribution and lower charge collection efficiency.
What are the key factors contributing to the narrow efficiency distribution observed in the devices?
The narrow efficiency distribution is attributed to the high reproducibility of the water-spreading LBL process, which ensures consistent film thickness and morphology across multiple devices. The ambient processing conditions also reduce variability caused by environmental fluctuations. Additionally, the optimized vertical phase separation minimizes batch-to-batch variations in charge transport and collection.
How does the device stability (84.1% retention after 1000 hours) compare to state-of-the-art OSCs, and what degradation mechanisms are mitigated?
The 84.1% retention after 1000 hours is among the best reported for ambient-processed OSCs, comparable to devices fabricated under inert conditions. The improved stability is likely due to the enhanced vertical phase separation, which reduces photo-oxidation at the interfaces, and the absence of residual solvents that can degrade the active layer. The water-spreading process may also result in a more compact film morphology, limiting oxygen and moisture ingress.
What are the potential scalability challenges when transitioning from 1 cm2 devices to larger-area modules, and how does this method address them?
Scaling to larger areas typically introduces issues such as increased series resistance and non-uniform film thickness. The water-spreading method inherently provides a self-limiting and uniform film formation, which can be adapted to roll-to-roll processing. The demonstrated 1 cm2 device with 16.56% PCE indicates minimal efficiency loss with area, suggesting that the method is amenable to scaling. However, further optimization of electrode patterning and module design is required to minimize resistive losses in larger modules.
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