Organic Solar Cells Breakthrough: 20.82% Efficiency and High Thickness Tolerance
Recent advancements in organic solar cells (OSCs) have led to a significant increase in their power conversion efficiency (PCE), breaking barriers once thought difficult to overcome. In a recent study published in Nature Materials, researchers have achieved an impressive 20.82% efficiency in single-junction OSCs. This breakthrough is achieved through a novel method of manipulating the crystallization sequence of the active layer, which allows for better performance across a variety of thicknesses. The findings of this study not only advance the efficiency of OSCs but also open doors for their industrial-scale application, particularly for large-area solar panels.
Key Highlights
20.82% Efficiency: A certified power conversion efficiency of 20.82% has been achieved in single-junction organic solar cells.
High Thickness Tolerance: The method allows OSCs to maintain strong performance even with active layer thicknesses ranging from 100–400 nm.
Crystallization Sequence Manipulation: Introducing a semiconductor regulator, AT-β2O, helps control the crystallization order of the donor and acceptor materials in the active layer.
Improved Charge Carrier Mobility: The new method optimizes vertical phase separation in thick films, resulting in better balance between electron and hole transport.
LBIC Mapping Insights: LBIC (light-beam-induced current) mapping, provided by infinityPV, revealed stronger and more uniform photocurrent distribution in ternary modules compared to binary ones.
Slot-Die Coating for Large-Area Modules: Slot-die coating was employed for fabricating large-area OSC modules, enabling uniform, ~250 nm-thick active layers without post-processing.
Large-Area Solar Modules: This innovation led to a large-area module (15.03 cm²) with an impressive 18.36% efficiency, paving the way for scalable solar panel production.
Long-Term Stability: The devices exhibit excellent operational stability, retaining 83% of their initial efficiency after 1,200 hours of aging.
Universality: The approach has been successfully applied across different active layers, solvents, and processing techniques, showcasing its broad applicability.
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Introduction: Overcoming Active Layer Thickness Challenges
Organic solar cells have seen tremendous growth in recent years due to the development of small-molecule acceptors and improved device engineering. However, a common challenge has been the performance drop when the active layer is thickened—an issue that hampers large-scale production, where thicker layers are often necessary to prevent pinholes. This research presents a solution that allows OSCs to maintain efficiency even with thicker active layers, making them more suitable for industrial-scale applications.
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Crystallization sequence manipulation involves controlling the order in which the donor and acceptor materials crystallize in the active layer of organic solar cells. By using a semiconductor regulator like AT-β2O, researchers can ensure that the materials crystallize in a way that enhances vertical phase separation. This results in better charge carrier mobilities, improved charge transport, and overall higher efficiency, even in thicker films.
Study Methodology: Crystallization Sequence Manipulation
To address the challenge of thickness tolerance, the researchers introduced a novel organic semiconductor regulator, AT-β2O, into the active layer blend of donor material D18-Cl and acceptor N3. The role of AT-β2O is to manipulate the crystallization sequence of the donor and acceptor materials. In a typical binary blend, D18-Cl and N3 crystallize simultaneously, potentially leading to poor charge transport in thicker films. By adding AT-β2O, the N3 crystallizes behind D18-Cl, promoting a more favorable bulk-heterojunction (BHJ) structure with enhanced vertical phase separation.
This manipulation results in the formation of a donor-rich phase near the substrate, a uniform BHJ region in the middle, and an acceptor-rich phase at the top of the active layer. This separation is crucial for improving charge carrier mobilities and balancing electron and hole transport, thus increasing efficiency and thickness tolerance.
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Results: Efficiency and Stability Achievements
The results from this study are groundbreaking. The team achieved a certified PCE of 20.43% in single-junction OSCs, with a thickness tolerance of 100–400 nm. Even at thicker layers, the devices retained efficiencies above 19%, a significant improvement compared to conventional organic solar cells, which often lose performance with increasing thickness.
Not only was efficiency improved, but the stability of the devices was also enhanced. The devices retained 83% of their initial efficiency after 1,200 hours of aging, marking a significant advancement in the long-term viability of OSCs for real-world applications.
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Large-Area Modules: A Step Toward Industrial-Scale Production
One of the major hurdles in OSC development has been scaling up the technology for large-area applications. The ability to print large-area modules without sacrificing performance is a critical step toward commercialization. In this study, the team successfully fabricated a 15.03 cm² module with a certified efficiency of 18.04%. LBIC (light-beam-induced current) mapping, provided by infinityPV, was utilized to analyze the photocurrent distribution across these modules. The results revealed that the ternary module (D18-Cl:N3:AT-β2O) exhibited a stronger and more uniform photocurrent distribution compared to the binary module (D18-Cl:N3). This uniformity and enhanced performance are pivotal for advancing OSC scalability.
The team also utilized slot-die coating during the fabrication process. This method allowed for the production of uniform, ~250 nm-thick active layers at a coating speed of 20 mm/s with a gap height of 50 μm in ambient air. Notably, no additional post-processing steps were required, demonstrating the scalability and practicality of this approach for industrial production.
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Conclusion: A Bright Future for Organic Solar Cells
This study marks a significant milestone in the development of organic solar cells, offering a solution to the long-standing problem of efficiency loss in thicker active layers. By manipulating the crystallization sequence, the researchers have created a more stable, efficient, and scalable solar cell design that holds promise for industrial applications. With efficiencies exceeding 20%, these cells could soon play a significant role in renewable energy production, particularly in large-scale solar panel installations.
Authors:
Haiyang Chen
Yuting Huang
Rui Zhang
Hongyu Mou
Junyuan Ding
Jiadong Zhou
Zukun Wang
Hongxiang Li
Weijie Chen
Juan Zhu
Qinrong Cheng
Hao Gu
Xiaoxiao Wu
Tianjiao Zhang
Yingyi Wang
Haiming Zhu
Zengqi Xie
Feng Gao
Yaowen Li
Yongfang Li
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