The exceptional performance realized by this triple-junction architecture is particularly notable considering its scalability and cost-effectiveness compared to traditional high-efficiency cells. Kerem Artuk, the lead author of the study and an EPFL alumnus now at CSEM, emphasizes that this design mirrors the performance of the most advanced space-grade III-V multi-junction solar cells, which typically achieve efficiencies near 37% yet demand materials and manufacturing processes that are prohibitively expensive for terrestrial applications. By contrast, this perovskite-silicon hybrid approach offers a promising path toward high-efficiency photovoltaics at a fraction of the cost.

Achieving this milestone was anything but straightforward. Conventional triple-junction cells are often constrained by low voltage output in the upper cell and insufficient current in the middle cell, limitations that historically capped their overall performance. To address these challenges, the EPFL-CSEM team implemented three innovative modifications to the cell’s material and optical structure. First, they introduced a specialized molecule during perovskite formation, effectively guiding crystal growth and eradicating defects that typically hinder voltage enhancement. This led to a remarkable boost in the top cell’s voltage, reaching 1.4 volts under sunlight—a significant leap forward in perovskite cell technology.

The second breakthrough involved a novel three-step fabrication process tailored for the middle perovskite cell, meticulously engineered to augment light harvesting in the near-infrared domain, a spectral region previously underserved in multi-junction devices. This refinement dramatically enhances the cell’s current generation capabilities, directly impacting the overall power conversion efficiency. Complementing this, the third innovation strategically positioned nanoparticles between the bottom silicon layer and the middle perovskite cell. These nanoparticles act as reflective agents, redirecting otherwise lost photons back into the middle layer, thereby elevating its absorption efficiency and current output.

Beyond the technical marvels, this advancement signals a paradigm shift toward making high-efficiency solar technology accessible and practical for everyday use. Both perovskite materials and silicon substrates benefit from mature, cost-effective manufacturing routes, especially when contrasted with the specialized, costly III-V semiconductor processes which dominate in aerospace applications. With this scalable, low-cost fabrication blueprint, the door opens for multi-junction photovoltaics to transition from satellite-exclusive solutions to mainstream commercial and residential energy systems.

The project, spearheaded by Christian Wolff and his team at EPFL, is not merely a demonstration of power conversion efficiency but a holistic illustration of integrating fundamental science with cutting-edge engineering. Their ongoing roadmap includes pursuing scale-up strategies in partnership with CSEM, alongside rigorous durability assessments crucial for real-world deployment. The researchers aim to ensure these high-performing cells can maintain their stability and performance over extended operational lifetimes, addressing one of the most significant barriers facing perovskite technologies.

This breakthrough also rekindles enthusiasm for multi-junction solar cells’ potential, which theoretically can exceed 40% efficiency by optimizing material combinations and photon management strategies. The silicon-perovskite system, bolstered by tailored crystallization techniques and photonic enhancements, brings this optimistic projection within tangible reach. Notably, this achievement represents a five-fold improvement over the group’s 2018 prototype, which initially demonstrated a modest 13% efficiency, underscoring rapid advancements in materials science and device engineering over a relatively short period.

Fundamentally, the triple-junction design capitalizes on the complementary absorption spectra of each semiconductor layer. The top perovskite tuned for high voltage, the middle perovskite maximizing near-infrared capture, and the silicon bottom cell harvesting the remaining longer-wavelength light—together, this stratified architecture efficiently converts a broader segment of the solar spectrum. The strategic deployment of nanoparticles further refines the internal light environment, exemplifying how photon and carrier management synergistically elevate device performance.

This research heralds an era where perovskite-based multi-junction solar cells do not merely rival but surpass existing terrestrial photovoltaics in both performance and cost-efficiency. Moreover, the potential to fine-tune these cells for specialized applications—including space missions where weight, efficiency, and cost are critically balanced—positions this innovation at the confluence of academic inquiry and industrial transformation.

Refining the fabrication process to be scalable and integrating robustness into these cells will be the next critical milestones. The collaboration between EPFL and CSEM is actively exploring these avenues, envisioning seamless incorporation of the technology into commercial products. The team’s multidisciplinary approach—merging materials chemistry, optical physics, and precision engineering—embodies the Swiss tradition of excellence and innovation in renewable energy technologies.

In conclusion, this triple-junction solar cell breakthrough is more than a record in energy conversion efficiency—it symbolizes a transformative advance in photovoltaic science. By harnessing perovskite materials’ versatility and silicon’s reliability, combined with innovative optical engineering, this research sets a new paradigm for cost-effective, high-performance solar energy solutions that are scalable for widespread adoption. As the push for sustainable energy intensifies globally, innovations such as these catalyze the transition toward cleaner, more affordable power sources for the planet’s future.

Subject of Research: Advancement in triple-junction perovskite-silicon solar cells achieving record efficiency through novel material and photonic engineering.

Article Title: Triple-junction solar cells with improved carrier and photon management

News Publication Date: 17-Mar-2026

Web References:

• Nature Article DOI: 10.1038/s41586-026-10385-y
• EPFL PV-Lab
• CSEM

Image Credits: © Kerem Artuk

Keywords

Triple-junction solar cell, perovskite photovoltaics, silicon solar cell, multi-junction efficiency, photon management, carrier management, scalable manufacturing, high-efficiency solar energy, renewable energy technology, photovoltaic innovation

At the core of this innovation lies the Cu₂AgBiI₆ material, a member of the rapidly emerging class of lead-free perovskite-inspired semiconductors. Unlike traditional lead-based perovskites, which pose environmental and toxicity concerns, Cu₂AgBiI₆ offers a non-toxic alternative without compromising on the optoelectronic properties necessary for efficient solar energy conversion. Its intrinsic structural stability and suitable bandgap allow it to absorb sunlight effectively, making it a promising candidate for next-generation solar cells. The research team’s success in leveraging this material for flexible substrates represents a crucial stride towards eco-friendly, versatile solar technologies.

One of the most compelling aspects of the study lies in the fabrication process developed to realize flexible Cu₂AgBiI₆ solar cells on a large scale. Typically, perovskite solar cells require highly controlled, small-batch environments due to their sensitivity to moisture and other environmental factors. However, the researchers devised scalable solution-processing techniques adaptable for roll-to-roll manufacturing, which is compatible with flexible substrates like polyimide films. This achievement is significant because it bridges the gap between laboratory prototypes and industrial production, enabling mass-market viability for flexible photovoltaics.

The mechanical flexibility of the Cu₂AgBiI₆-based devices is not merely a proof of concept but emerges as a key functional attribute. The solar cells maintain high power conversion efficiencies even under repeated bending and deformation, showcasing remarkable mechanical robustness. This trait opens avenues for integrating solar cells into unconventional surfaces and wearable electronics, where rigidity has typically limited the deployment of conventional silicon and brittle perovskite solar panels. By combining mechanical flexibility with environmentally safe materials, this work paves the way for solar harvesting in diverse applications ranging from fabrics to mobile devices.

In terms of performance metrics, the flexible solar cells deliver promising power conversion efficiencies that rival those of their rigid counterparts. The authors report that the Cu₂AgBiI₆ devices achieve substantial photovoltaic efficiency while retaining stability under mechanical stress and ambient conditions. This balanced performance stems from meticulous optimization of the material’s crystallinity, film morphology, and interface engineering with charge transport layers. These technical advancements have culminated in devices that not only perform well but also withstand operational stresses expected in real-world environments.

Another highlight of the research is the comprehensive analysis of the electronic properties of the Cu₂AgBiI₆ thin films. Through advanced characterization techniques such as transient photoluminescence and impedance spectroscopy, the team dissected charge carrier dynamics and recombination mechanisms within the perovskite-inspired layer. These insights informed the refinement of the processing parameters, minimizing defect densities and enhancing charge extraction efficiency. This level of understanding is crucial for pushing the boundaries of performance in emerging photovoltaic materials, enabling iterative improvements in device design.

Crucially, the incorporation of silver (Ag) and bismuth (Bi) into the copper iodide matrix produces a complex but beneficial alteration in the semiconductor’s electronic structure. This tailored chemistry influences band alignment and defect tolerance, enabling the solar cell to harvest light more effectively across the visible spectrum. Such compositional engineering exemplifies how material science innovations drive renewable energy technology forward by customizing fundamental properties at the atomic scale.

Sustainability considerations also underpin the research, as the lead-free composition addresses environmental concerns that have shadowed traditional perovskite solar cells. The selection of earth-abundant and less hazardous elements makes the technology more suitable for large-scale deployment without the risks of lead contamination during manufacture, usage, and disposal. Furthermore, the low-temperature solution processes reduce energy consumption during production compared to silicon photovoltaics, reinforcing the green credentials of this flexible solar technology.

The promise of integrating these flexible solar cells into wearable electronics is particularly exciting. The ability to conform to curved surfaces while maintaining energy conversion efficiency means that future devices such as smart clothing, portable power sources, and internet-of-things sensors could harness ambient light to operate autonomously. This convergence of materials science and flexible electronics significantly expands the scope of solar energy beyond static installations, embedding it seamlessly into daily life.

Looking ahead, the researchers emphasize continuing efforts to improve device lifetime and stability under prolonged environmental exposure. Although the current Cu₂AgBiI₆ solar cells exhibit encouraging durability, further encapsulation strategies and interface passivation techniques are needed to mitigate degradation pathways under moisture and ultraviolet light. Such advances will be vital for commercial applications, where long-term reliability is a determining factor in technology adoption.

The scalability demonstrated by the roll-to-roll processing methods developed in this study is particularly noteworthy. This manufacturing approach not only expedites production but also lowers costs, potentially making flexible solar cells accessible for widespread use. The translation of lab-scale fabrication to industrially viable processes remains a persistent challenge in the field of perovskite photovoltaics, and this work represents a significant leap forward.

Collaborative efforts combining material synthesis, device engineering, and advanced characterization were pivotal to this achievement. The interdisciplinary approach underscores the complexity of developing new solar cell technologies and highlights the necessity of convergence between chemistry, physics, and engineering disciplines. Such collaborative paradigms are increasingly important for addressing the multifaceted challenges associated with transitioning to sustainable energy systems.

The study’s findings also serve to inspire further investigation into other perovskite-inspired compounds that could offer complementary or superior properties. Exploring alloying, doping, and dimensional modifications could unlock new functionalities and efficiencies. Thus, the demonstrated success with Cu₂AgBiI₆ provides a foundational framework upon which the entire family of lead-free perovskite-inspired materials can evolve.

In conclusion, the flexible Cu₂AgBiI₆-based solar cells introduced by Holappa and colleagues mark a transformative development in photovoltaic technology. Their innovative large-scale processing methods coupled with environmentally benign, mechanically robust materials lay the groundwork for the next generation of flexible, sustainable energy solutions. These breakthroughs have the potential to revolutionize how and where solar energy is harnessed, integrating it more intimately into our lives while advancing the global drive towards clean energy.

Subject of Research:
Flexible perovskite-inspired solar cells using Cu₂AgBiI₆ material, focusing on large-scale fabrication methods and mechanical flexibility.

Article Title:
Flexible Cu₂AgBiI₆-based perovskite-inspired solar cells using large-scale processing methods.

Article References:
Holappa, V., Grandhi, G.K., Lamminen, N. et al. Flexible Cu₂AgBiI₆-based perovskite-inspired solar cells using large-scale processing methods. npj Flex Electron (2025). https://doi.org/10.1038/s41528-025-00505-5

Image Credits:
AI Generated

Addressing this challenge, a team of researchers led by Ying, Su, Li, and colleagues has developed a pioneering antisolvent-seeding method that fundamentally transforms the fabrication process of flexible monolithic perovskite/CIGS tandem solar cells. This novel technique intricately decouples the self-assembled monolayers (SAMs) adsorption from their dissolution processes while simultaneously embedding perovskite seeding directly into the assembly. Their work, recently published in Nature Energy, unveils a methodology that not only navigates the complex surface morphology of flexible CIGS substrates but also dramatically enhances the wettability, crystallinity, and adhesion of the perovskite layers—which are crucial parameters governing the efficiency and durability of tandem solar cells.

At the core of this breakthrough lies a sophisticated manipulation of solvent polarity dynamics. The research team employed a high-polarity solvent to dissolve the SAMs without inducing deleterious clustering, which typically compromises uniformity during layer formation. Concurrently, they introduced a low-polarity antisolvent environment to encourage the formation of high-density SAMs during the adsorption stage. This delicate balance ensures that the SAMs form a well-organized, densely packed monolayer on the roughened surface of the flexible CIGS cells, which is essential for promoting uniform perovskite nucleation and growth.

One of the critical insights from this work is the recognition that seeding—the process of initiating crystal formation in the perovskite layer—is vital for achieving optimal film quality on challenging substrates. By incorporating a pre-mixed seed layer into the assembly process, the team substantially improved the overall wettability of the perovskite precursor solution on the underlying SAMs. This enhancement in wettability facilitates more homogeneous nucleation, thereby reducing defects and grain boundaries that typically plague flexible perovskite layers. The subsequent improvement in crystallinity leads to more efficient charge transport pathways and reduced recombination losses within the solar cell architecture.

The integration of these layered advancements culminated in the successful fabrication of a flexible monolithic perovskite/CIGS tandem solar cell with an active area of 1.09 cm². The device exhibited a stabilized power conversion efficiency (PCE) of 24.6%, with a certified efficiency of 23.8%, situating it competitively alongside the best-performing rigid perovskite/CIGS tandem cells globally. This milestone firmly establishes flexible perovskite/CIGS tandems as not just experimental curiosities but practical contenders in the arena of high-performance, thin-film photovoltaic technologies.

Beyond efficiency metrics, the durability of photovoltaic devices plays a pivotal role in their commercial viability and long-term functionality. The flexible tandem cells produced using this antisolvent-seeding technique demonstrated exceptional operational stability, retaining over 90% of their initial efficiency after 320 hours of continuous operation. Furthermore, mechanical resilience tests revealed that the devices could endure 3,000 bending cycles at a tight radius of 1 cm without significant degradation in performance. Such mechanical endurance is particularly significant for applications necessitating repeated flexing, such as wearable devices, rollable displays, or curved architectural integrations.

The success of this antisolvent-seeding strategy extends beyond immediate performance gains. It represents a fundamental advance in the understanding and engineering of interfacial chemistry and materials science in perovskite solar cells. The precise control over SAM adsorption and dissolution offers a versatile platform for manipulating surface energetics, crystalline orientation, and interface quality—all factors that critically impact photovoltaic efficiency and stability.

This research also opens exciting avenues for further exploration and optimization. For example, the principles underlying solvent polarity modulation and seed layer integration could be extrapolated to other perovskite compositions or alternative thin-film absorber materials, potentially unlocking new performance regimes or enabling entirely novel device architectures. Additionally, the scalable nature of the approach aligns well with industrial manufacturing processes, suggesting a feasible pathway towards commercial production of flexible tandem solar cells.

Critically, the ability to produce flexible, efficient, and durable tandem solar cells holds profound implications for the renewable energy sector’s ongoing quest to reduce carbon emissions and promote sustainable energy solutions. Lightweight and adaptable solar devices could significantly expand deployment options, including integration into vehicles, portable power systems, and building-integrated photovoltaics, effectively bringing solar energy harvesting capabilities closer to end-users in diverse environments.

Moreover, the tandem configuration itself—a stack of two absorber layers with complementary spectral absorption—is a strategic approach to surpassing the efficiency limits of single-junction solar cells. By effectively harnessing a broader range of the solar spectrum, tandem devices can convert sunlight into electricity more efficiently, thereby maximizing the utility and economic viability of photovoltaic installations.

The interdisciplinary collaboration underlying this research, blending expertise in materials chemistry, surface science, and device physics, underscores the complexity of contemporary solar cell innovation. It also highlights the importance of precision engineering at the nanoscale to solve macroscale energy challenges—a narrative increasingly defining the future of clean energy technologies.

Looking forward, the adaptation of this antisolvent-seeding methodology in conjunction with emerging perovskite compositions or tandem structures involving silicon or other semiconductor technologies could drive photovoltaics to new heights. This capability to marry materials innovation with practical device engineering could catalyze a paradigm shift in how solar power systems are conceptualized, manufactured, and deployed globally.

In sum, the work presented by Ying, Su, Li, and colleagues marks a significant milestone in flexible photovoltaics, demonstrating that the longstanding barriers associated with rough, flexible CIGS surfaces can be surmounted through clever chemical and materials engineering. Their antisolvent-seeding approach not only achieves record efficiencies but also promises the mechanical robustness necessary for real-world applications. This development thus propels flexible perovskite/CIGS tandem solar cells from laboratory curiosities to promising candidates for next-generation renewable energy technologies poised to make a substantial impact on the global energy landscape.

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Subject of Research: Flexible monolithic perovskite/Cu(In,Ga)Se₂ (CIGS) tandem solar cells and their fabrication via antisolvent seeding of self-assembled monolayers (SAMs).

Article Title: Antisolvent seeding of self-assembled monolayers for flexible monolithic perovskite/Cu(In,Ga)Se₂ tandem solar cells.

Article References:
Ying, Z., Su, S., Li, X. et al. Antisolvent seeding of self-assembled monolayers for flexible monolithic perovskite/Cu(In,Ga)Se₂ tandem solar cells. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01760-6

Image Credits: AI Generated