A research team from Fudan University has explored a novel optimization method for the transport layer in solar cells, challenging the conventional view that high extraction barriers lead to low power conversion efficiency. Through extensive simulations (10 000) and experimental validations, researchers demonstrated that efficient charge separation remains achievable even with extraction barriers as high as 0.3 eV by minimizing voltage drops in the transport layer. By optimizing thickness to compensate for an electron extraction barrier of 0.27 eV, they achieved a 24.6% efficiency, validating the practicality of their theoretical framework. This work opens new avenues for the development of cost-effective, high-performance photovoltaic devices.
Solar cells, as a vital renewable energy technology, hold broad application prospects. However, their conversion efficiency has long been a key bottleneck constraining their development. A critical components in these devices is the the transport layer (TL), which facilitates the extraction of photogenerated charge carriers. Historically, it was believed that energy offsets or barriers exceeding 0.026 eV in TLs significantly hinder charge extraction, thereby reducing power conversion efficiency (PCE)... However, this view is not entirely accurate and experimental observations have sometimes contradicted this understanding, with certain solar cells displaying enhanced performance despite high barriers. This inconsistency has posed a fundamental challenge: how can high energy barriers be reconciled with the quest for efficient charge extraction? The lack of a unified design principle has impeded the rational development of transport layers capable of overcoming these barriers, ultimately limiting device performance and material choices.
An appropriate parameter optimization can overcome the negative effects of barriers and achieve efficient charge separation. Consequently, the solar cell transport layer optimization method proposed in this paper challenges conventional thinking, offering new insights and paradigms for solar cell material selection.
The Solution: Addressing this challenge, this study introduces a universal design principle: minimizing the voltage drop across the transport layer. Through detailed computational modeling of over 10,000 simulated solar cells, the researchers demonstrate that high extraction barriers, up to 0.3 eV, can be effectively compensated by optimizing TL parameters. Crucially, efficiency losses are not directly determined by the barrier itself, but rather by the voltage drop it induces across the TL. Key strategies include reducing the TL thickness, and increasing its carrier mobility and dielectric constant. This approach ensures efficient charge separation and transfer, even in the presence of substantial barriers.
To simplify this complex design principle, the researchers developed an evaluation metric θ, which integrates TL parameters into a single, easy-to-use figure of merit. This parameter enables rapid assessment and optimization of transport layers, making the design of high-efficiency solar cells more accessible and adaptable to practical manufacturing.
This factor integrates multiple key parameters such as extraction barrier height, transport layer thickness, carrier mobility, and dielectric constant—into a single, easily computable metric via formula (1).
The theoretical findings were also experimentally validated in perovskite solar cells. The authors synthesized a novel dual-cable polymer named ETL-1 as the electron transport layer, which exhibits an extraction barrier of 0.27 eV in the solar cell. At a thickness of 16 nm, performance was significantly compensated, achieving a high efficiency of 24.6%, comparable to the barrier-free PCBM reference device (25.0%). This case strongly demonstrates that the presence of an extraction barrier should not automatically disqualify a transport layer material. Consequently, the study broadens the scope of materials suitable for transport layers, facilitating more cost-effective and versatile solar cell designs.
The Future: This research underscores a transformative insight: the detrimental effects of high extraction barriers are not insuperable. By strategically tuning transport layer properties to minimize voltage drops, it is possible to realize high-efficiency solar cells with a variety of material systems. This advancement paves the way for more flexible, low-cost, and scalable photovoltaic technologies.
Looking ahead, the authors emphasize the importance of developing new, low-cost non-fullerene transport materials and refined carrier transport models. These will support better material selection and device optimization, particularly for emerging perovskite and organic solar cell technologies. Ultimately, this universal design principle could accelerate the commercialization of high-performance, accessible solar energy solutions worldwide
The Impact: In the future, we can anticipate further research efforts to explore methods and technologies for optimizing the transport layer in solar cells, thereby enhancing their conversion efficiency and advancing the development of clean energy.
The research has been recently published in the online edition of Materials Futures , a prominent international journal in the field of interdisciplinary materials science research.
Reference: Ruichen Yi, Zhijie Hu, Jia Zhang, Feng-Yu You, Tiankai Zhang, Bo Ma, Guangrui Zhu, Chunqin Zhu, Shaobo Liu, Xianxi Yu, Wen Feng, Yuan Pei, Anran Yu, Yiqiang Zhan, Weiwei Li, Jiajun Qin, Xiaoyuan Hou. Unlocking the Potential of Transport Layers in Solar Cells: A Universal Design Principle for High Efficiency Despite High Extraction Barriers[J]. Materials Futures . DOI:10.1088/2752-5724/ae3ab8
Materials Futures
Unlocking the Potential of Transport Layers in Solar Cells: A Universal Design Principle for High Efficiency Despite High Extraction Barriers
20-Jan-2026