In the evolving landscape of renewable energy technologies, flexible tandem solar cells represent a beacon of innovation, promising to deliver lightweight, highly efficient power solutions that adapt to diverse applications from wearable electronics to aerospace. Among these, perovskite and copper indium gallium selenide (CIGS) tandem solar cells stand out due to their complementary absorption spectra and potential for cost-effective manufacturing. However, one persistent challenge has notably hindered the realization of their scalable potential: the integration of high-quality perovskite top cells onto the inherently rough and structurally complex surfaces of flexible CIGS bottom cells.
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
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