In an era where sustainable and efficient energy sources are paramount, advances in photovoltaic technologies are critical. A team of researchers spearheaded by the Institute of Physics at the Chinese Academy of Sciences has unveiled a groundbreaking approach to enhance the performance and scalability of semi-transparent perovskite solar cells, particularly those based on the all-inorganic CsPbI₃ perovskite. Their pioneering work introduces a novel MoOx/Ag/MoOx (MAM) sandwich-structured buffer layer that dramatically improves both the efficiency and durability of semi-transparent CsPbI₃/TOPCon tandem solar cells.
The challenge with perovskite solar cells (PSCs) lies not only in achieving high power conversion efficiencies but also in addressing long-term operational stability and scalability for practical applications. Traditional hybrid perovskites—comprising mixed organic and inorganic components—are plagued by issues such as phase segregation, ion migration, and poor crystallinity, which accelerate degradation and reduce device longevity. The all-inorganic CsPbI₃ perovskite emerges as a superior alternative due to its enhanced thermal stability and resistance to phase segregation, offering a more robust material platform for tandem solar cell architectures.
Yet, developing scalable, semi-transparent CsPbI₃ devices with competitive efficiencies has remained elusive, particularly for mechanistically stacked tandem modules at practical device sizes. One crucial bottleneck is the damage inflicted during the deposition of transparent conductive oxides (TCOs) via magnetron sputtering onto organic charge transport layers. This process can compromise the underlying layers, limiting device lifespan and performance. Conventional buffer layers like MoOx provide some protection but suffer from limited charge transport capabilities, increased parasitic absorption, and present challenges when scaled up.
Addressing these obstacles, the research team engineered a sandwich-like MAM buffer structure whereby a thin silver (Ag) layer is encapsulated between two MoOx layers. This design not only safeguards the fragile organic layers beneath from sputtering damage but also enhances charge carrier transport and optical transparency. A key discovery was the in-situ formation of Ag₂MoO₄ within the MAM layer during fabrication, which acts as an efficient carrier transport facilitator while maintaining high visible light transmission between 400 and 800 nm. This fine-tuned balance of electrical and optical properties is critical for optimizing semi-transparent solar cells.
The improved MAM buffer layer facilitated semi-transparent CsPbI₃ solar cells to achieve a remarkable power conversion efficiency (PCE) of 18.86% on small active areas (0.50 cm²). More impressively, when integrated into a four-terminal (4-T) mechanically stacked tandem cell with a TOPCon silicon bottom cell, the devices exhibited a combined PCE of 26.55%. Such efficiencies represent a significant milestone, underlining the potential of this sandwich structure in merging perovskite and silicon technologies effectively.
Beyond small devices, scalability was demonstrated by fabricating larger-area minimodules with aperture sizes of 6.62 cm². These modules maintained impressive efficiencies of 16.67% for the semi-transparent CsPbI₃ perovskite top cells and 26.41% for the complete 4-T tandem minimodules. Notably, this marks the first reported instance of minimodule demonstrations for this particular device architecture, a critical step towards commercial viability and real-world application of perovskite/silicon tandems.
Stability is a paramount concern for perovskite technologies, often restraining their commercial adoption. The new MAM buffer layer also provides a significant advancement here. Mini-modules retained over 93% of their initial performance after more than 1,000 hours of storage, indicating robust long-term environmental resilience. Such stability ensures that devices can withstand practical operating conditions, including temperature fluctuations and light exposure, fundamental for deployment.
The structural design of the MAM buffer layer not only protects the perovskite and adjacent layers but also optimizes optical management. By enhancing visible transmittance without compromising electrical properties, the buffer layer allows for effective light harvesting in both sub-cells of the tandem device. This synergy between structural design and optical-electrical functionality is essential to push the frontier of tandem solar cell efficiencies further.
Looking ahead, the research signals future directions in transparent and photostable interfacial materials aimed at directly integrating the top and bottom cells electrically in series configurations. This would simplify tandem architectures and potentially reduce fabrication complexity and costs. Additionally, alternative fabrication techniques such as doctor blading and slot-die coating are envisioned to produce higher-quality large-area CsPbI₃ films suitable for scalable production.
Scientific inquiries will also focus on the development of new functional buffer layers that minimize efficiency losses related to interfacial defects and parasitic absorption. The pursuit of Ag-free buffer designs is especially pertinent, given the cost and scarcity considerations of precious metals. Finding cheaper, earth-abundant alternatives while retaining the unique benefits of the MAM sandwich configuration could revolutionize the buffer layer’s role in perovskite tandem solar cells.
The realization of mechanistically stacked 4-T tandem mini-modules with record efficiencies and advanced stability demonstrates the feasibility of translating laboratory-scale innovations into practical, scalable photovoltaic devices. This breakthrough paves the way for next-generation perovskite-based tandem solar cells to achieve widespread adoption in the renewable energy landscape, offering a highly efficient, cost-effective, and durable alternative to conventional photovoltaics.
Published in the international journal Materials Futures, this research sets a new benchmark for the design of buffer layers in perovskite photovoltaic technology. It underscores the critical interplay of material science, device engineering, and scalable fabrication technologies necessary for commercializing high-performance solar cells. The insights from this study can expedite the integration of perovskite/silicon tandem photovoltaics into diverse applications, from building-integrated photovoltaics to large-scale solar power plants.
In summary, the MoOx/Ag/MoOx sandwich buffer layer stands as a transformative innovation in the quest for high-efficiency, scalable, and stable semi-transparent perovskite solar cells and tandem modules. By combining protective, electrical, and optical functionalities in a single tailored layer, this technology addresses long-standing challenges in perovskite solar cell fabrication and opens new avenues for the practical realization of next-generation photovoltaics.
Subject of Research: MoOx/Ag/MoOx sandwich structured buffer layers for high efficiency semi-transparent CsPbI₃-based perovskite solar cells and four-terminal tandem minimodules.
Article Title: Designing MoOX/Ag/MoOX sandwich structured buffer layer for four-terminal CsPbI3/TOPCon tandem minimodules
News Publication Date: 16-Oct-2025
Web References:
http://dx.doi.org/10.1088/2752-5724/ae0c76
References:
Rui Zhang, Bobo Ma, Yuqi Cui, Chengyu Tan, Bingbing Chen, Yiming Li, Jiangjian Shi, Huijue Wu, Yanhong Luo, Dongmei Li, Jianhui Chen, and Qingbo Meng*. Designing MoO_X/Ag/MoO_X sandwich structured buffer layer for four-terminal CsPbI_3/TOPCon tandem minimodules. DOI: 10.1088/2752-5724/ae0c76
Image Credits: Rui Zhang, Dongmei Li and Qingbo Meng from Institute of Physics, Chinese Academy of Sciences, and Bobo Ma and Jianhui Chen from Hebei University.
Keywords
Hybrid solar cells, Perovskites, Semi-transparent tandem solar cells, CsPbI₃ perovskite, TOPCon tandem minimodules, MoOx/Ag/MoOx buffer layer, Power conversion efficiency, Charge carrier transport, Scalable perovskite photovoltaics, Four-terminal tandem solar cells, Photovoltaic stability, Transparent conductive oxides
