Tandem solar cells generate electricity by stacking materials that absorb different portions of sunlight. In the reported architecture, a wide-bandgap perovskite cell is placed on top of a Cu(In,Ga)Se₂, or CIGS, bottom cell. The perovskite captures much of the visible spectrum, while CIGS absorbs lower-energy near-infrared photons that pass through the top layer. This division of the solar spectrum can produce more electrical power than a conventional single-junction cell, whose efficiency is constrained by the trade-off between light absorption and voltage generation.

Although the concept is highly promising, the two-terminal monolithic design is difficult to manufacture. The subcells must be physically integrated, optically aligned and electrically connected through an intermediate recombination layer. Any roughness on the textured CIGS surface, incomplete film coverage or defect-rich boundary can cause carriers to recombine before they are collected. These interface losses reduce the tandem’s voltage and fill factor, while also creating pathways for chemical degradation. The new study focuses on controlling these losses at both critical junctions rather than optimizing only one side of the device.

The first part of the strategy uses a nanoparticle-assisted nickel oxide, or NiOₓ, intermediate recombination layer. NiOₓ serves as a hole-selective material and helps connect the perovskite top cell with the CIGS bottom cell. However, depositing a uniform ultrathin layer over a textured semiconductor surface can be challenging. The researchers used nanoparticles to improve the layer’s ability to follow the underlying topography, producing more conformal coverage and reducing exposed regions where unwanted recombination or electrical leakage could occur.

The intermediate layer must do more than simply connect the two subcells. It needs to support efficient transport of holes from one absorber while allowing electrons from the other absorber to recombine with them in a controlled way. This process, known as interfacial recombination, electrically links the subcells in a monolithic tandem. According to the study, the engineered NiOₓ layer helped optimize the energy-level alignment between adjacent materials, lowering transport barriers and improving the extraction of photogenerated carriers. Better alignment can increase the voltage retained by the tandem and reduce resistive losses during operation.

The second part of the approach targets the boundary between the perovskite absorber and C₆₀, a fullerene-based electron-transport material commonly used in perovskite solar cells. Defects at this interface can act as traps, capturing electrons and holes and allowing them to recombine without contributing to the external current. The researchers introduced a bimolecular co-passivation treatment designed to neutralize multiple types of interfacial defects at the same time. By chemically stabilizing the contact and modifying its electronic properties, the treatment reduced trap-assisted recombination and promoted more efficient electron extraction into C₆₀.

The combined effect of the two interface treatments produced a champion small-area tandem with a reported efficiency of 31.09%. Independent certification measured the device at 30.57%, while its steady-state efficiency reached 30.32% under continuous operation. The active area of this device was 0.0539 square centimetres. Importantly, the strategy also translated to a larger device measuring 1.0298 square centimetres, which achieved a reported efficiency of 29.44% and a certified value of 28.85%. Maintaining performance as device area increases is a major challenge because larger cells are more vulnerable to coating defects, current non-uniformity and resistance losses.

The results are particularly notable because efficiency was not achieved at the expense of durability. The optimized devices retained approximately 94% of their initial efficiency after more than 3,500 hours of storage. Under continuous operation, they preserved about 91% of their starting performance after more than 750 hours. When heated to 70 degrees Celsius, the devices retained roughly 90% of their efficiency after 960 hours. These tests suggest that suppressing interfacial defects can improve both carrier transport and resistance to degradation, although longer testing under standardized outdoor conditions will be needed to determine how the cells perform over years of real-world use.

The study demonstrates that interface engineering may be one of the most effective routes toward practical perovskite/CIGS tandem photovoltaics. Rather than treating the boundaries between layers as passive connections, the researchers designed them as active components that control energy alignment, defect chemistry, carrier recombination and mechanical coverage. The combination of nanoparticle-assisted NiOₓ and bimolecular co-passivation addresses two different bottlenecks in the same device, helping bridge the gap between laboratory-scale efficiency records and scalable tandem manufacturing. If the approach can be adapted to larger modules and industrial deposition processes, it could accelerate the development of high-efficiency solar panels capable of converting a broader fraction of sunlight into electricity.

Subject of Research: Interface engineering for efficient and stable monolithic perovskite/Cu(In,Ga)Se₂ tandem solar cells

Article Title: Improving interface-mediated carrier transport for efficient perovskite/Cu(In,Ga)Se₂ tandem solar cells

Article References: Zeng, L., Wang, W., Tang, L. et al. Improving interface-mediated carrier transport for efficient perovskite/Cu(In,Ga)Se₂ tandem solar cells. Nature Energy (2026). https://doi.org/10.1038/s41560-026-02125-3

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-026-02125-3

Keywords: Perovskite solar cells, Cu(In,Ga)Se₂, tandem photovoltaics, interface engineering, NiOₓ, C₆₀, carrier transport, defect passivation, solar-cell stability, photovoltaic efficiency

At the core of this research lies an intricate understanding of how electrical and material properties at the interface between perovskite and adjacent charge transport layers influence device longevity. The team identifies that one critical factor undermining stability is the mismatch in dielectric constants between the perovskite layer and the commonly used fullerene derivative layer, C60. This discrepancy creates sharp discontinuities in the interfacial electric field when the device operates under reverse bias, specifically during partial shading conditions that are typical in everyday use. Such sudden shifts in electric potential can trigger voltage breakdowns, accelerating degradation pathways that compromise the solar cell’s structural and functional integrity.

Delving into the physics of reverse-bias degradation, the researchers reveal that these abrupt field discontinuities facilitate enhanced carrier tunneling across the perovskite/C60 interface. This tunneling current, under stress, promotes undesirable interface reactions including the migration and accumulation of halide ions—mobile species notorious for inducing defects and material instabilities within perovskite structures. The migration of halides under electric field and thermal effects exacerbates degradation mechanisms, manifesting in loss of photovoltaic performance and irreversible damage. Therefore, controlling the interface’s electrostatic landscape emerges as a pivotal strategy to curb these pathways.

To counteract these detrimental effects, the authors innovate by introducing graded dielectric layers between the perovskite and the C60 electron transport layer. Unlike conventional abrupt junctions, these graded layers present a continuum in dielectric constant values, effectively smoothing the electric field profile across the interface. This tailored gradient eliminates sharp potential drops, thereby mitigating abnormal band bending phenomena. Consequentially, the driver for carrier tunneling diminishes, substantially reducing undesirable tunneling currents and attenuating the halide ion accumulation that previously jeopardized stability.

Notably, the implementation of graded dielectric layers did not come at the expense of device efficiency. On the contrary, their optimized tandem solar cells demonstrated exceptional power conversion efficiencies of 34.18% and 34.03%, confirmed by certifications and verified across different silicon bottom-cell architectures—silicon heterojunction and tunnel oxide passivated contact designs respectively. This marks a significant milestone, showcasing that enhanced stability and ultra-high efficiency can co-exist in perovskite/silicon tandem solar cells, addressing what has been a major trade-off in the field.

Beyond efficiency improvements, the study rigorously validates the durability of these advanced devices under harsh reverse-bias conditions. Subjected to stress tests at a voltage of -15 V for 1,000 hours, tandem cells equipped with graded dielectric interfaces retained over 92% of their initial efficiency. This represents an unprecedented resilience to reverse-bias degradation, highlighting the practicality of the approach for real-world photovoltaic applications where partial shading and electrical stress are unavoidable operational realities.

The research further demonstrates scalability by fabricating a large-area multi-cell string that attained an impressive 31.00% efficiency. This larger module maintained over 90% of its efficiency after enduring the same extensive reverse-bias stress for 1,000 hours, underscoring the potential for industrial adoption. Scaling stability improvements from small cells to multi-cell assemblies is crucial for transforming laboratory advances into impactful commercial technology, and this study bridges that gap convincingly.

Underlying these advances is a sophisticated interplay of materials science and device engineering. By carefully selecting and engineering graded dielectric materials that harmonize the electric field distribution, the researchers create a barrier against ion migration and electrical instabilities. This deepened understanding of interfacial physics informs not only current architectures but also sets a precedent for designing next-generation interfaces in various layered optoelectronic devices.

The implications of this work extend significantly into the photovoltaic industry’s drive towards higher system reliability and extended device lifetimes. Stability under reverse-bias stress has long limited the deployment and trustworthiness of tandem solar modules, especially in environments where shading from buildings, trees, or passing objects frequently induces partial shading. Strategies that suppress voltage breakdown and degradation mean fewer performance losses, lower maintenance costs, and greater investor confidence in perovskite/silicon tandem technologies.

Furthermore, this stability enhancement aligns well with the goals of integrating tandem solar cells into modern energy grids. The ability to endure electrical stress while maintaining performance facilitates easier incorporation into systems that dynamically optimize power output under fluctuating environmental conditions. As smart grids and distributed energy resources proliferate, reliable tandem cells become even more crucial assets.

Wang and colleagues’ study sets a new standard for addressing the persistent challenge of stability in tandem photovoltaics. By marrying intricate material design with practical device fabrication, this research not only boosts power conversion efficiency but also ensures that these promising solar cells can withstand the real-world stresses that have historically impeded their commercialization. The innovative graded dielectric layer solution catalyzes a paradigm shift in tandem solar cell engineering, pointing the way toward resilient, cost-effective, and high-performance photovoltaic systems.

As industry and academia push forward, this work could inspire further exploration into diverse dielectric materials and interface structures to tailor electrical properties with even greater precision. The principles demonstrated in smoothing electric fields and mitigating interfacial ion migration may also translate to other emerging photovoltaic materials and devices vulnerable to electric stress-induced degradation. Thus, this approach potentially heralds broad advancements beyond perovskite/silicon tandems alone.

In sum, the breakthrough achieved by Wang et al. illustrates the power of strategic interface engineering in overcoming one of the most formidable hurdles facing perovskite/silicon tandem solar cells. Their creation of graded dielectric layers not only resolves the issue of electric field discontinuities but decisively curtails reverse-bias induced tunneling and halide ion movement—elements crucial to unlocking tandem solar cells’ full commercial and environmental potential. By demonstrating robust stability coupled with record efficiencies in both small cells and large-area modules, this study advances the very foundation of efficient, durable solar energy conversion and accelerates the leap from laboratory innovation to market-ready clean energy solutions.

Subject of Research: Stability enhancement in monolithic perovskite/silicon tandem solar cells under reverse-bias stress through graded dielectric interface engineering.

Article Title: Improving the stability of monolithic perovskite/silicon tandems against reverse-bias stress using graded dielectric layers.

Article References:
Wang, L., Yu, Z., Wang, N. et al. Improving the stability of monolithic perovskite/silicon tandems against reverse-bias stress using graded dielectric layers. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02067-w

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-026-02067-w

The cornerstone of this innovative approach lies in the molecular design and assembly of self-assembled monolayers (SAMs), a class of ultrathin organic coatings known to tune interfacial properties. Traditional SAMs, while effective in modifying surface energies and facilitating charge extraction, suffer from inherent shortcomings linked to their crystalline or highly ordered nature. The crystallinity, though beneficial for charge transport, often leads to discontinuities at the interface, weak adhesion, and pathways conducive to ion migration—factors that culminate in device degradation and failure under prolonged operation or dynamic bias conditions.

Addressing the limitations of conventional SAMs, the research team has synthesized and characterized a pair of phosphonic acid derivatives: (4-(7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid, denoted as CbzNaph, alongside its hydroxyl-functionalized analogue, CbzNaphOH. The presence of intramolecular hydrogen bonding in CbzNaphOH is a deliberate molecular engineering feat designed to introduce steric hindrance and subtle distortions in molecular packing. This steric effect discourages the formation of a crystalline SAM and instead favors the assembly of an amorphous, yet densely packed, multilayer structure—termed a-SAMUL.

The amorphous nature of this self-assembled multilayer brings several critical advantages. Firstly, it forms a homogeneously packed interface, minimizing structural defects and grain boundaries where ion migration typically initiates. Secondly, the a-SAMUL demonstrates notably strong adhesion between the perovskite layer and the substrate, enhancing mechanical robustness and suppressing delamination under operational stresses. These properties collectively mitigate the formation and migration of mobile ionic species within the device, a dominant degradation pathway in perovskite photovoltaics.

Comprehensive spectroscopic analyses, including X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray scattering, elucidate the distinct molecular packing and electronic environment conferred by the a-SAMULs. These investigations reveal that the tailored interfacial layer maintains excellent energy-level alignment with the hole transport layer, facilitating efficient hole extraction while blocking electrons—a crucial attribute for high fill-factor and open-circuit voltage in solar cells.

Device fabrication integrating the a-SAMUL into the architecture of perovskite solar cells yielded remarkable improvements. Certified power conversion efficiencies (PCEs) surpassing 26% were achieved, placing these cells among the highest performing in the field. More significant, however, was the enhancement in operational stability and breakdown voltage. The devices exhibited reverse bias breakdown voltages exceeding −17 V, a threshold far superior to conventional SAM-modified cells, indicating pronounced resistance to voltage-induced degradation.

Accelerated aging tests conducted under continuous illumination and maximum power point tracking demonstrated outstanding durability, with the a-SAMUL-based devices maintaining over 90% of their initial efficiency beyond 3,000 hours. This stability surpasses typical operation timeframes documented for state-of-the-art perovskite solar cells, underscoring the transformative potential of amorphous multilayer interfaces in real-world applications.

Underlying these performance gains is the suppression of ion migration, a pervasive and detrimental phenomenon in perovskite materials. Ion migration leads to dynamic changes in internal electric fields, causing hysteresis, irreversible chemical reactions at interfaces, and phase segregation within the perovskite lattice. The homogeneous and densely packed a-SAMUL acts effectively as a physical and chemical barrier, preventing the diffusion of mobile ions and stabilizing interfacial charge dynamics.

The molecular design benefits extend beyond merely electromechanical stabilization. The hydroxyl functionalization in CbzNaphOH, combined with the spacer length and intermolecular hydrogen bonding, is critical for the formation of multilayer self-assembled films rather than monolayers. This multilayering effect results in an unusual balance of amorphous order and dense packing, which had not been previously reported as a feature in SAM engineering for optoelectronic devices.

This discovery redefines the paradigm of molecular interface engineering in perovskite solar technology. Instead of seeking perfect order and crystallinity, which historically guided SAM design, inducing controlled amorphousness emerges as a powerful strategy offering mechanical flexibility, defect tolerance, and enhanced ion-blocking capabilities. These insights pave the way for the systematic development of next-generation self-assembled materials that combine chemical functionality with tailored morphology to meet the stringent operational requirements of advance photovoltaics.

Further implications of this work extend to device architectures beyond perovskites. The principles of amorphous multilayer formation and tailored molecular packing may be adapted to other thin-film technologies such as organic photovoltaics and light-emitting diodes, where interface control is equally paramount. The modular chemical synthesis approach to phosphonic acid derivatives also allows for fine-tuning of interfacial electronic properties, thereby facilitating customized device optimization.

In concert with advancements in device encapsulation and perovskite compositional engineering, these robust hole-selective interlayers represent a critical component in overcoming the commercialization bottleneck of perovskite photovoltaics. By delivering unprecedented stability under high reverse bias conditions, a-SAMULs reduce the risk of catastrophic failure modes encountered in real-world module operation, enhancing safety and reliability.

The broader scientific community stands to benefit from these findings, as they exemplify how subtle molecular engineering can translate into macroscale performance enhancements and reliability. Future work will likely explore the interplay between molecular structure, multilayer thickness, and environmental stability, as well as scaling these interfaces for large-area device fabrication without sacrificing uniformity or performance.

This breakthrough reflects a synthesis of chemical ingenuity, materials science, and device engineering that heralds a new era for perovskite solar cells, enabling them to edge ever closer to commercial viability with record efficiencies and formidable stability. As the global demand for sustainable energy continues to surge, these developments illuminate a promising pathway toward cost-effective, high-performance solar technologies capable of widespread adoption.

By reimagining the role of self-assembled molecular layers, the study propels the field toward a horizon where long-term operational durability and top-tier efficiency coexist, marking a pivotal step in unlocking the full potential of perovskite photovoltaics.

Subject of Research: Perovskite solar cells – Interface engineering and stability enhancement through amorphous self-assembled multilayers.

Article Title: Amorphous self-assembled multilayers for perovskite solar cells with improved reverse bias stability.

Article References:
Feng, Q., Liu, KK., Wang, D. et al. Amorphous self-assembled multilayers for perovskite solar cells with improved reverse bias stability. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02015-8

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41560-026-02015-8

The driving force behind this advancement is the newly designed multifunctional additive, 4-F-PEAFa. This compound plays a pivotal role in creating two distinct bridges at the interfaces between the perovskite and the transport layers—one for holes and another for electrons. Historically, inefficient charge transport has been linked to poorly managed interfaces, leading to energy losses and complicated fabrication processes. The innovative use of 4-F-PEAFa allows both interfaces to be engineered with the same molecule, streamlining the fabrication process while simultaneously enhancing performance.

At the perovskite/hole transport layer interface, the first molecular bridge facilitates rapid hole extraction, which is crucial for maintaining charge balance and minimizing recombination rates. The second bridge at the perovskite/electron transport layer interface is designed to improve electron mobility, further ensuring that charge carriers can seamlessly move through the cell’s structure. The dual role played by this single compound is significant; it reduces material complexity and enhances the overall efficiency of the solar cell.

Achieving a champion efficiency of 26% marks a remarkable milestone in the development of perovskite solar cells. This performance surpasses previous records and positions the technology as a leading contender in the energy sector. Moreover, the certified efficiency of 25.6%, along with an impressive fill factor of 0.88, indicates that these devices are not only efficient but also capable of producing a substantial amount of energy. Such advancements reinforce the viability of perovskite-based technology as a worthy competitor against traditional solar technologies.

In addition to efficiency, the stability of solar cells remains a critical hurdle for widespread adoption. The research team’s findings on the longevity of their devices are equally promising. Unencapsulated samples exhibited over 90% retention of initial efficiency after enduring 2000 hours at high temperatures of 85°C and 1000 hours of continuous operation. This level of durability addresses one of the most significant barriers to commercialization, as it suggests that these solar cells can withstand harsh environmental conditions without significant degradation.

The implications of this research extend beyond mere efficiency gains. By confirming Herbert Kroemer’s famous assertion that “the interface is the device,” the study paves the way for innovative interface engineering within the realm of photovoltaics. This new strategy allows researchers and engineers to explore molecular configurations that enhance charge transport, potentially leading to breakthroughs in other areas of material science and nanotechnology.

The collaborative effort behind this research highlights the interdisciplinary nature of modern scientific inquiries. The leadership of Qing Lian from Southern University of Science and Technology, alongside co-first authors Lina Wang, Guoliang Wang, and Guojun Mi, underscores the importance of diverse scientific expertise. Their work, supported by co-corresponding authors from various prestigious institutions, reflects a concerted effort to tackle one of the pressing challenges in renewable energy technology through a unified approach.

Looking forward, the study’s findings present an exciting opportunity for further research into molecular additives and their roles in optimizing solar cell architectures. As the world continues to shift towards sustainable energy solutions, understanding the fundamental mechanisms behind charge transport will be crucial. The ongoing exploration of molecular bridges could inspire new innovations that reduce costs and improve system efficiency, thus accelerating the transition to renewable energy sources.

The promise of perovskite solar cells is not merely a theoretical construct but a tangible reality, and this study stands as a testament to what can be achieved when traditional boundaries are challenged. By adopting a fresh perspective on molecular engineering, the research team has unlocked new avenues for advancing solar technology.

This paradigm shift in perovskite solar cell technology not only poses the question of efficiency but also invites deeper contemplation about the future of clean energy. As nations vie for leadership in the renewable energy sector, breakthroughs like these will play an instrumental role in shaping the landscape of energy production, influencing policies, and inspiring the next generation of scientists and engineers to innovate further.

In conclusion, as researchers continue to refine and develop the interface mechanisms within solar cells, the dream of widespread, efficient, and stable renewable energy generation approaches realization. The dual molecular bridge strategy exemplifies how clever material science can lead to transformative changes not just in solar technology, but across the entire spectrum of applied sciences—ultimately contributing to a more sustainable future for all.

Subject of Research: Charge Transport in Perovskite Solar Cells
Article Title: Double Molecular Bridges Revolutionize Charge Transport in Perovskite Solar Cells
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Image Credits: ©Science China Press

Keywords

Perovskite Solar Cells, Charge Transport, Double Molecular Bridges, 4-F-PEAFa, Efficiency, Stability, Renewable Energy