Perovskite solar cells have long dazzled the photovoltaics community with their rapid efficiency gains, but the architecture of the device matters enormously. In the conventional n–i–p configuration, in which electrons are collected at the bottom and holes at the top, engineers routinely apply a mixed-dimensional heterojunction at the illuminated surface. This top layer, typically composed of low-dimensional perovskite phases interleaved with the three-dimensional absorber, passivates defects and improves charge extraction. But when researchers invert the stack to the p–i–n layout—often preferred for tandems because of processing advantages and compatibility with silicon bottom cells—the same trick largely fails. The reason is fundamental: most reported two-dimensional perovskites are intrinsically p-type, meaning their Fermi levels and band edges are misaligned with the electron transport layer that must sit directly beneath them in these inverted devices.

The new work tackles this mismatch head-on through electronic engineering of two-dimensional Ruddlesden–Popper perovskites, a family of layered materials in which sheets of corner-sharing metal halide octahedra are separated by organic cation spacers. Rather than accepting the native p-type character of these layers, the team induced a genuine p-to-n transition using two complementary strategies. The first relies on molecular dipole tuning: by incorporating parahalogenated piperidine derivatives—piperidine rings bearing halogen atoms at the para-like position of the aromatic substitution pattern—the researchers shifted the internal electric fields and charge distribution within the layered perovskite, steering the material’s Fermi level upward into n-type territory. The second strategy involves chemically designable n-type defects, deliberate point defects introduced in controlled fashion that donate electrons to the lattice and stabilize the n-type character.

The consequences of this electronic flip cascade through the entire device. With an n-type 2D capping layer atop the wide-bandgap perovskite absorber, the energy-level alignment at the perovskite–electron transport layer interface improves dramatically. Electrons, which must cross this boundary to be collected, encounter far lower energetic barriers than before. The tailored band alignment simultaneously suppresses non-radiative recombination, the parasitic process in which photogenerated carriers annihilate at interfacial traps, releasing their energy as heat rather than light. For wide-bandgap perovskites—here approximately 1.68 electronvolts, chosen to pair optimally with silicon—non-radiative losses at this interface have been the dominant ceiling on open-circuit voltage. Removing them pays off directly in the numbers.

Indeed, the p–i–n wide-bandgap perovskite solar cells built with the n-type 2D capping layer delivered open-circuit voltages enhanced by more than 100 millivolts compared with control devices. In a field where efficiency records are often broken by fractions of a percentage point, a hundred-millivolt gain is a seismic shift, and it translated into a certified power conversion efficiency of 33.64% when the perovskite top cell was integrated with an industrial-grade silicon bottom cell. The silicon component was no laboratory curiosity: the team used 110-micrometer-thick Czochralski-grown heterojunction silicon wafers, the workhorse material of mainstream photovoltaic manufacturing. Czochralski silicon, produced by pulling a single crystal from a melt, is the industry standard precisely because it is cheap and scalable, even though it contains more defects than the float-zone silicon often used in record-setting laboratory cells. Demonstrating world-class tandem performance on such commercially realistic wafers strengthens the path from lab to factory.

Stability, the perennial Achilles heel of perovskite technology, also benefited. The molecular engineering that converts the 2D layer to n-type simultaneously enhances the material’s robustness, and the monolithic perovskite/silicon tandem cells retained 92% of their initial efficiency after 1,100 hours of continuous operation under maximum-power-point tracking. This testing protocol, which continuously extracts the maximum available power as conditions evolve, is far more demanding than simple open-circuit storage and closely mimics real-world deployment. Encapsulated tandem modules that hold more than nine-tenths of their output over well over a thousand hours of continuous illumination represent performance in the range where commercial warranties begin to look defensible.

The scientific significance of the work lies in its demonstration that the electronic character of two-dimensional perovskites is not an immutable property but a designable parameter. Ruddlesden–Popper perovskites have been prized as passivating and moisture-resistant layers since the earliest days of perovskite photovoltaics, yet their utility has been constrained by the assumption that their band structure favors hole transport. By showing that molecular dipoles and defect chemistry can be combined to invert that preference, the researchers have effectively expanded the toolkit available to device designers. The parahalogenated piperidine derivatives act as more than passive spacers; their bond dipoles reshape the electrostatic landscape of the inorganic sheets, and the rationally introduced n-type defects complete the conversion. The strategy is chemical, modular, and in principle transferable to other layered halide systems and other interfaces throughout the device stack.

For the perovskite/silicon tandem field specifically, the achievement addresses the long-standing tension between the two architectures. Tandem devices stack a wide-bandgap perovskite cell on top of a silicon cell so that each harvests the portion of the solar spectrum it converts most efficiently; the perovskite captures blue and green photons while silicon collects the red and infrared. Theoretical analyses suggest such tandems can surpass the single-junction Shockley–Queisser limit of roughly 33% by comfortable margins, and laboratory records have climbed steadily past 34%. The p–i–n configuration is attractive for manufacturing because it permits low-temperature processing on silicon and avoids some stability issues associated with high-temperature transport layers, but its performance has lagged. By resolving the interfacial energetics that held p–i–n devices back, the new results suggest that this industrially favored architecture can now compete at the very highest efficiency levels, and do so on commercially standard silicon.

The voltage gains also carry implications beyond tandems. Wide-bandgap perovskites near 1.68 electronvolts are the workhorses of tandem top cells, but in single-junction form they suffer from severe voltage deficits caused by defect-tolerant yet trap-limited carrier dynamics. The demonstration that a purpose-built n-type 2D surface layer can recover more than 100 millivolts suggests a generalizable prescription for any device where the electron extraction interface is the loss center—single-junction cells, light-emitting diodes operating in reverse, and photoelectrochemical systems alike. Because the treatment is applied through molecular additives and defect design rather than exotic processing, it should be compatible with existing coating and deposition workflows.

What remains to be seen is how the chemistry scales. Parahalogenated piperidine derivatives must be synthesized, purified and incorporated reproducibly at manufacturing scale, and long-term field testing will need to confirm that the benefits observed under laboratory maximum-power-point tracking persist through thermal cycling, humidity and ultraviolet exposure in the field. But the certified 33.64% efficiency, the industrial silicon wafer, and the 1,100-hour stability result together mark a milestone in the maturation of perovskite/silicon tandem photovoltaics. By treating the electronic type of a two-dimensional perovskite as a tunable parameter rather than a fixed constraint, the work opens a molecular-level route to optimizing interfacial energetics—one that brings the long-promised era of high-efficiency, stable, manufacturable tandem solar cells measurably closer.

Perovskites are a family of semiconductors whose crystal structures can be tuned by mixing different ions. Their strong absorption, adjustable bandgaps and ability to form thin films have made them leading candidates for tandem solar cells, in which two light-absorbing devices are stacked so they can harvest different portions of sunlight. Silicon is particularly effective at converting lower-energy visible and near-infrared light, while a wide-bandgap perovskite top cell can absorb higher-energy photons before they reach the silicon layer. In principle, this division of labor allows a tandem device to produce more electricity than either material could generate alone. In practice, wide-bandgap perovskite top cells often suffer from a voltage deficit: the voltage delivered by the operating solar cell falls significantly below the energy expected from the material’s optical bandgap. Non-radiative recombination, in which excited electrons and holes lose their energy as heat rather than light or electrical current, is a major cause.

The new approach focuses on the anionic sublattice, the network of negatively charged ions that helps define the perovskite crystal’s structure and electronic environment. Rather than treating these anions as passive components, the researchers designed perovskite derivatives containing cyanate anions with dynamic disorder. This means that the anions are not locked into a single perfectly static arrangement within the lattice. Their changing local configurations can influence how the material crystallizes and how charges move through it. The researchers used this behavior to alter crystallization kinetics—the rates and pathways by which a thin film transforms from a precursor mixture into an ordered semiconductor. According to the study, this dynamic anionic engineering directed the formation of a coherent bulk heterojunction, a continuous internal architecture in which related semiconductor regions are intimately connected rather than separated into poorly matched domains.

That structural control matters because the microscopic quality of a perovskite film determines how efficiently it handles photogenerated charge. During crystallization, imperfections can form at grain boundaries, where individual crystalline regions meet, and at interfaces between different materials. These sites can contain electronic defects known as trap states. Deep-level traps are especially damaging because they can capture electrons or holes and facilitate non-radiative recombination, shortening the time available for charges to reach the electrical contacts. A solar cell may therefore absorb sunlight efficiently while still losing much of the resulting energy before it becomes usable current. The cyanate-containing materials were designed to act at these vulnerable locations. The study reports that the anions provided chemical and electronic passivation at grain boundaries and interfaces, effectively neutralizing deep-level traps and suppressing the recombination pathways that create voltage losses.

The film morphology produced by the method was also important. The researchers observed large-grained material, meaning the perovskite contained relatively broad crystalline regions with fewer grain boundaries per unit area. Large grains do not automatically guarantee a high-performing solar cell, because defects can still occur within crystals or at contacts, but reducing the total density of boundaries can limit the number of locations where charge carriers become trapped. The reported coherent bulk heterojunction adds another layer of control by creating a connected internal structure that supports charge transport across the absorber. Together, the crystallization pathway, grain growth and interfacial passivation address different parts of the same problem: keeping photogenerated carriers mobile and preventing them from dissipating their energy before extraction.

The performance results show how those chemical and structural changes translated into working devices. A single-junction wide-bandgap perovskite solar cell made using the method reached a power conversion efficiency of 24.35%. Power conversion efficiency is the fraction of incident sunlight converted into electrical power, and in a wide-bandgap perovskite cell it reflects the balance among current generation, voltage, and the fill factor, which describes how effectively the device maintains useful power across its operating range. The more consequential result came when the perovskite was placed above a silicon cell in a monolithic tandem architecture. Because the two subcells are connected within a single integrated device, the top perovskite layer must transmit suitable light to the silicon beneath it while generating a high voltage of its own. The tandem reached 34.79% efficiency in the reported measurements, and a certified value of 34.29% provided an independently validated benchmark.

Tandem photovoltaics are attractive partly because they can surpass the practical efficiency ceiling of conventional single-junction silicon. A single semiconductor absorbs photons over a limited energy range: photons below its bandgap pass through or are weakly absorbed, while excess photon energy above the bandgap is lost as heat. Stacking materials with different bandgaps reduces both forms of loss. Yet this design also increases the number of interfaces and processing constraints. The top perovskite must be deposited without damaging the silicon device, remain optically and electrically compatible with the lower cell, and withstand illumination, heat and electrical stress over time. Wide-bandgap compositions have been particularly challenging because increasing the bandgap can intensify chemical instability and promote non-radiative losses. By engineering the anion chemistry rather than relying solely on broad compositional adjustments, the researchers sought to improve efficiency and stability through the same underlying material design.

Durability testing provided a second major result. Under the ISOS-L-1 protocol, which evaluates operational stability under continuous illumination, the tandem retained 95% of its initial performance after 1,100 hours. The study also reports more than 1,300 hours of extended real-world testing under the ISOS-O-2 protocol. Stability measurements are crucial for perovskite technology because impressive initial efficiencies have often been accompanied by rapid performance declines. Perovskite crystals and their interfaces can respond to light, temperature and electric fields, with ions moving through the lattice or chemical reactions developing at contacts. Such changes can create new defects, alter the distribution of elements and undermine the electrical properties of the device. The reported retention under both continuous illumination and longer-duration real-world conditions suggests that the cyanate-based design may suppress several degradation pathways, although the timescales remain short compared with the operational lifetimes expected of commercial solar modules.

The significance of the work is therefore broader than a single efficiency record. It demonstrates that the negative-ion framework of a perovskite can be deliberately designed to control processes occurring at multiple scales, from the motion and disorder of individual anions to the crystallization of the full absorber and the behavior of interfaces in a tandem device. The researchers describe this strategy as dynamic anionic sublattice engineering, emphasizing that anions can actively shape the formation and operation of the semiconductor. That concept could help materials scientists move beyond a trial-and-error search through combinations of elements. By selecting anions for their effects on crystallization, defect chemistry and electronic passivation, researchers may be able to design perovskites around specific performance requirements. In this case, the approach was aimed at the stability–performance trade-off, the tendency for improvements in efficiency to be offset by faster degradation.

The new results do not by themselves establish that perovskite–silicon tandems are ready for mass deployment. Commercialization will still depend on manufacturing uniform large-area films, protecting devices from moisture and heat, maintaining performance across millions of cells and demonstrating long-term reliability under diverse climates. Certified laboratory efficiency and controlled stability testing are essential milestones, but they are not substitutes for years of field operation. Even so, the study offers a compelling blueprint for tackling the materials problems that stand between laboratory devices and practical solar power. By using dynamically disordered cyanate anions to guide crystallization, passivate defects and support a coherent heterostructure, the researchers produced a tandem cell that combines unusually high efficiency with substantial short-term operational retention. If the chemistry can be translated to scalable manufacturing, engineering the anionic sublattice could become one of the most important tools for turning perovskite–silicon tandems from high-performance experiments into a durable source of low-carbon electricity.

Triple-junction solar cells are designed to capture a broader portion of sunlight than conventional single-junction devices. Instead of relying on one absorber to convert all usable photons, the architecture stacks three sub-cells with different bandgaps. A wide-bandgap perovskite at the top absorbs higher-energy visible photons, a second perovskite layer converts a different part of the solar spectrum, and a crystalline silicon bottom cell captures lower-energy near-infrared light. When these sub-cells are connected in series, the voltages generated by each junction add together. However, the current is limited by the sub-cell producing the lowest current, making both electronic quality and optical design critical to overall performance.

The researchers focused first on the top wide-bandgap perovskite, where defects at or near the surface can severely reduce the voltage of a solar cell. These defects create electronic states inside the material’s bandgap. Photogenerated electrons and holes can become trapped at these states and recombine before they contribute to an external current. This process, known as non-radiative recombination, releases energy as heat rather than light and lowers the quasi-Fermi-level splitting, a key measure of the maximum voltage that a photovoltaic absorber can generate under illumination.

To suppress these losses, the team introduced a passivating molecule known as 4F-POEABr. The molecule contains an ammonium group that can interact with the perovskite surface and an electron-deficient molecular structure designed to influence the local electronic environment. According to the researchers, these features provide two complementary forms of protection. Chemical passivation reduces the activity of defect sites, while field-effect passivation changes the distribution of electrical charge near the surface, making it more difficult for electrons and holes to encounter one another and recombine.

The effect was reflected in the electronic quality of the treated wide-bandgap perovskite. The material reached a quasi-Fermi-level splitting of 1.53 electron volts, indicating a substantial reduction in voltage loss under illumination. When incorporated into a sub-cell, it produced an open-circuit voltage of 1.413 volts. Open-circuit voltage is measured when no current is drawn from the device, and in high-efficiency solar cells it provides a direct indication of how effectively the absorber preserves photogenerated charge. Achieving a high voltage in a wide-bandgap perovskite is especially important because the top cell must generate substantial voltage while transmitting suitable light to the sub-cells beneath it.

The study also tackles a less visible but equally important problem: how light travels through the stack. In a triple-junction device, photons pass through multiple transparent electrodes, transport layers, perovskite absorbers and interconnection layers before reaching the silicon cell. At every boundary, light can be reflected, transmitted or absorbed. Because the thicknesses and refractive indices of these layers determine how waves interfere with one another, even nanometre-scale changes in a layer can alter the amount of light reaching a particular sub-cell.

The researchers used systematic interference management to increase the current generated by the middle perovskite sub-cell, which limited the current of the series-connected device. Their approach involved tailoring a bilayer made from tin oxide and indium zinc oxide. These transparent conducting and electron-transport components were selected and arranged to modify the optical field inside the stack. By controlling reflection and transmission at the interfaces, the redesigned structure delivered an additional 0.5 milliamperes per square centimetre from the current-limiting middle junction. In a triple-junction device, such a gain can be decisive because excess current from one sub-cell cannot compensate for a shortage in another when all junctions operate in series.

The reported efficiencies show the importance of combining chemical and optical engineering rather than treating them as separate challenges. A device can have excellent material quality yet lose performance if its layers prevent sunlight from reaching the correct absorber. Conversely, sophisticated light management cannot recover voltage lost through severe non-radiative recombination. In the new architecture, molecular passivation improves the voltage contribution of the wide-bandgap top cell, while the tin oxide/indium zinc oxide structure improves current balance through the stack. The two strategies reinforce one another, allowing more of the incident solar energy to be converted into electrical power.

The researchers further report negligible hysteresis, meaning that the measured efficiency showed little dependence on whether the voltage was scanned upward or downward. This behavior is important because hysteresis can make photovoltaic performance difficult to evaluate and may signal charge accumulation or unstable ionic movement within perovskite layers. The devices also incorporated robust interconnection layers and engineered interfaces between the perovskite components. These design elements were intended to improve operational stability and reduce variation from one device to another, two requirements that become increasingly demanding as laboratory-scale cells expand toward commercial dimensions.

The larger-area result is particularly notable because performance often declines when devices grow. Defects, non-uniform coating, resistance in transparent electrodes and alignment errors can all become more consequential over a wider surface. The certified 26.97% steady-state efficiency measured across 15.62 square centimetres therefore suggests that the approach is not limited to a small demonstration area. Although further work will be required to establish long-term outdoor durability, manufacturing compatibility and large-module performance, the study presents a clear roadmap for improving sophisticated tandem architectures: protect the perovskite interfaces, control the electrical environment at defect-rich surfaces and design every transparent layer with both photons and charges in mind. Together, these advances move perovskite/perovskite/silicon triple-junction solar cells closer to the high efficiencies promised by multi-junction photovoltaics.

Subject of Research: Perovskite/perovskite/silicon triple-junction solar cells, molecular defect passivation and optical interference management.

Article Title: Defect passivation and optical management of triple-junction solar cells

Article References: Xu, Y., Wang, Z., Deng, C. et al. Defect passivation and optical management of triple-junction solar cells. Nature (2026). https://doi.org/10.1038/s41586-026-11010-8

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11010-8

Keywords: Perovskite solar cells, triple-junction photovoltaics, silicon solar cells, defect passivation, 4F-POEABr, wide-bandgap perovskites, non-radiative recombination, optical management, interference engineering, solar-cell efficiency.

The study, conducted by researchers from Southwest Petroleum University, Tongwei Solar (Chengdu) Ltd., the Shanghai Institute of Microsystem and Information Technology of the Chinese Academy of Sciences, and collaborating institutions, examined how changing outdoor spectra influence two-terminal, or 2T, perovskite/silicon tandems. The work was published online on May 9, 2026, in eScience Energy. Rather than relying solely on the standard test conditions used to rate solar cells, the researchers combined laboratory measurements, long-term outdoor sunlight data, device modeling, and economic simulations to estimate how tandem cells would perform under geographically and seasonally varying skies.

The central challenge arises from the architecture of a 2T tandem. In these devices, a high-energy perovskite sub-cell is stacked on top of a lower-energy silicon sub-cell. The perovskite layer preferentially absorbs shorter-wavelength, higher-energy photons, while silicon captures much of the red and near-infrared portion of the spectrum that passes through. The two sub-cells are connected in series, meaning that the same electrical current must flow through both. If one layer produces less current than the other, the weaker sub-cell limits the output of the entire device. This current-matching requirement makes 2T tandems particularly sensitive to changes in the spectrum of incoming sunlight.

Sunlight is not spectrally constant. Clouds, atmospheric aerosols, water vapor, air mass, seasonal solar angles, and local geography can all alter the balance of wavelengths reaching the ground. A blue-rich spectrum may favor one sub-cell, while a red-rich spectrum may favor the other. Under these conditions, a tandem can experience “spectral mismatch,” in which the current generated by the perovskite and silicon layers no longer aligns. A cell that performs impressively under the internationally standardized sunlight spectrum used in laboratories may therefore produce less energy per watt when exposed to the changing skies of an actual solar farm.

To measure this effect, the researchers fabricated 2T perovskite/silicon tandem cells and tested them with a tunable light-emitting diode solar simulator. The system allowed the team to reproduce standard illumination as well as blue-rich and red-rich sunlight conditions. Their experiments showed that current mismatch reached 4.98% under blue-rich illumination and 4.32% under red-rich illumination. Corrected measurements confirmed that both short-circuit current density and conversion efficiency were governed by the sub-cell generating the lower current. In practical terms, adding more photons to one portion of the spectrum does not necessarily increase tandem output if the other sub-cell cannot produce a comparable current.

The team then developed a model that combined the measured spectral response of the devices with a spectral mismatch factor, or MMF. Spectral response describes how efficiently a solar cell converts photons of different wavelengths into electrical current, while the MMF estimates how far real sunlight deviates from the reference spectrum used for testing. The model was applied to long-term solar-spectrum datasets from Haikou, Albuquerque, Yancheng, and Daqing. These locations represent contrasting photovoltaic environments, from warm and humid conditions to dry, high-altitude, temperate, and cold climates. The comparison revealed that the magnitude of spectral losses changes with location and operating conditions rather than remaining a fixed property of the tandem cell.

Because full spectral measurements are expensive and not widely available, the researchers also proposed a simpler way to estimate spectral risk. Their approach uses the ultraviolet ratio, calculated from ultraviolet irradiance and global horizontal irradiance. The analysis found a strong linear relationship between this indicator and tandem current mismatch. If validated across broader datasets, the method could allow developers to monitor spectral conditions using less complex equipment, helping them evaluate candidate sites and improve long-term energy forecasts without installing full spectroradiometric systems at every project.

The results show that spectral mismatch imposes an annual energy penalty of between 0.77% and 3.25% per watt compared with single-junction silicon. However, the overall picture remains favorable for tandems because their higher power density can compensate for these losses. Across the four representative climates, the tandem modules delivered 8.74% to 11.16% more annual energy per unit of land area than tunnel oxide passivated contact, or TOPCon, silicon cells. That distinction is important for utility-scale solar, where land availability, transmission access, foundations, cabling, and other balance-of-system costs can limit the amount of electricity produced by a project.

Economic modeling added another dimension to the analysis. In favorable regions, the improved land-use efficiency and potential savings on the direct-current side of the balance of system could reduce the levelized cost of electricity by as much as 1.59%. The model also indicated that tandem modules might support a price premium of up to 7% while remaining economically competitive with TOPCon silicon. The advantage was not universal, however, because local sunlight spectra, module prices, system design, and financing conditions all influence the final cost of electricity. A tandem that is highly attractive in one climate may offer a smaller economic benefit in another.

The researchers say the findings shift the discussion around tandem photovoltaics from a race for record laboratory efficiency toward a broader question: how reliably can these devices produce energy under real skies? Their framework links the physics of current matching with outdoor spectral measurements and project-level economics, offering manufacturers a way to design devices for specific climates and developers a method for comparing sites before construction. The study suggests that perovskite/silicon tandems are not defeated by changing sunlight, but they must be evaluated with that variability in mind. As solar power expands into land-constrained regions and high-demand electricity markets, understanding the colors of sunlight could become just as important as measuring the headline efficiency printed on a module datasheet.

Subject of Research: Two-terminal perovskite/silicon tandem solar cells under globally varying sunlight spectra

Article Title: Challenges of two-terminal perovskite/silicon tandem solar cells operating under globally varying spectral conditions

News Publication Date: May 9, 2026

Web References: ScienceDirect article; eScience Energy

References: DOI: 10.1016/j.esen.2026.100065

Image Credits: Chao Zhang, Jian Yu, et al.

Keywords

Perovskite solar cells, silicon photovoltaics, tandem solar cells, two-terminal tandems, spectral mismatch, solar spectrum, photovoltaic energy yield, TOPCon, levelized cost of electricity, renewable energy, solar technology, climate-dependent photovoltaics

A new study reports a possible route around that bottleneck by using thermal evaporation, a manufacturing technique already familiar to the semiconductor and display industries. In thermal evaporation, source materials are heated in a vacuum until they vaporize, allowing them to condense as controlled thin films on a target surface. The method can offer excellent thickness uniformity and precise compositional control, but it has been especially difficult to apply to formamidinium-based perovskites, which are among the most promising materials for tandem photovoltaics.

The central obstacle is formamidinium iodide, or FAI, a key precursor in many high-performing perovskite compositions. FAI must be heated sufficiently to evaporate, but excessive heat can cause it to thermally degrade before it reaches the substrate. That degradation can alter the chemical composition of the deposited film, disrupt crystal formation and create defects that reduce both efficiency and operational stability. According to the researchers, this problem has prevented thermal evaporation from being successfully demonstrated for large-area perovskite–silicon tandems.

The team addressed the challenge by synthesizing a formamidinium-based eutectic, a carefully formulated mixture whose components interact in a way that changes the material’s evaporation behavior. In this case, the eutectic lowers the effective evaporation temperature of FAI by an average of 36 degrees Celsius. That reduction brings the evaporation process below the compound’s degradation threshold, allowing FAI to enter the vapor phase without undergoing the thermal breakdown that has historically limited the technique.

This change is more than a small adjustment to the processing recipe. Stable evaporation is essential because the composition of a perovskite film must be controlled at the atomic scale. A slight imbalance between its organic, inorganic and halide components can affect the material’s crystal structure, electronic properties and resistance to environmental stress. By preventing FAI degradation during deposition, the eutectic approach enables the researchers to form films with enhanced crystallinity and greater compositional homogeneity, two characteristics closely linked to efficient charge extraction and reduced energy loss.

Using the modified evaporation process, the researchers fabricated sequentially deposited perovskite–silicon tandem cells with a steady-state efficiency of 31.5% over an area of 1 square centimetre. Steady-state measurements are particularly important in perovskite research because some devices can show transient performance that changes after illumination or electrical bias. A stable output at this level indicates that the evaporated perovskite layer can function effectively as the top cell in a high-performance tandem architecture rather than merely producing a brief peak measurement.

The larger-area results are even more significant for industrial development. The team produced what it describes as the first thermally evaporated large-area perovskite–silicon tandem on a commercial half-cut G12 wafer, achieving a steady-state efficiency of 30.0% across 200 square centimetres. Large-area devices are far more challenging than laboratory cells because defects, thickness variations and compositional inconsistencies have more opportunities to emerge as the surface expands. The relatively small difference between the small-cell and wafer-scale results suggests that the uniformity of the evaporation process can translate into strong area scalability.

Increasing the device area from 1 to 200 square centimetres produced a relative efficiency loss of only 3.99%. The researchers identify this as the lowest reported efficiency penalty for area scaling in perovskite-based tandems. That figure matters because a technology that performs brilliantly only on tiny samples may struggle to deliver competitive modules. A low scaling penalty indicates that the deposition process is not fundamentally dependent on laboratory-scale dimensions and could potentially be adapted to larger manufacturing platforms.

The devices also showed encouraging early evidence of durability. Under damp-heat testing at 85 degrees Celsius and 85% relative humidity, conditions designed to accelerate the degradation pathways that solar modules may encounter in the field, the eutectic-based tandem retained 95% of its initial efficiency after 2,000 hours. The tandem also exhibited negligible power loss during two months of real-world outdoor operation. Although longer testing across different climates and module configurations will be needed to establish commercial lifetimes, the results suggest that improved film uniformity and crystallinity may contribute to stronger environmental resilience.

The study points to a broader shift in perovskite manufacturing: instead of treating thermal evaporation as incompatible with sensitive organic precursors, researchers may be able to redesign the precursors themselves. By lowering the temperature required to evaporate FAI, the formamidinium eutectic turns a major chemical limitation into an engineering opportunity. The reported combination of 31.5% efficiency on small cells, 30.0% on a 200-square-centimetre wafer and limited performance loss under accelerated aging could bring thermally evaporated perovskite–silicon tandems closer to practical large-scale production. If the process can be integrated with high-throughput equipment and validated through extended field testing, it may help transform perovskite tandems from a laboratory breakthrough into a manufacturable next-generation solar technology.

Subject of Research: Thermally evaporated formamidinium-based perovskite/silicon tandem solar cells using a formamidinium eutectic.

Article Title: Thermally evaporated perovskite/silicon tandems via formamidinium eutectic

Article References: Luo, C., He, R., Ran, L. et al. “Thermally evaporated perovskite/silicon tandems via formamidinium eutectic.” Nature (2026). https://doi.org/10.1038/s41586-026-10970-1

Image Credits: AI Generated

DOI: 10.1038/s41586-026-10970-1

Keywords: Perovskite solar cells, silicon tandems, thermal evaporation, formamidinium iodide, eutectic materials, photovoltaic manufacturing, large-area solar cells, solar cell stability, damp-heat testing, renewable energy

A persistent challenge is that many high-performing indium-containing transparent conductive oxides (TCOs) raise cost and sustainability concerns, while silicon-based tunnel junctions can introduce parasitic optical losses. In a new study in Nature Energy, researchers report an alternative strategy built on titanium oxynitride, TiOxNy, designed to unify electrical, optical, and chemical functions in one material.

The key idea is to use conductive TiOxNy as a multifunctional recombination layer that improves charge transport in the vertical direction while suppressing unwanted lateral leakage. This matters for tandem stability because incomplete or inefficient recombination can increase carrier accumulation, degrade interfaces, and accelerate performance loss under continuous operation.

Beyond conductivity, the team emphasizes interfacial chemistry. TiOxNy provides anchoring sites for self-assembled monolayers (SAMs), achieved through a tridentate binding configuration. Those SAMs help engineer the energy landscape at the interface, strengthening contact selectivity and reducing recombination pathways that would otherwise waste photogenerated carriers.

Optically, the approach is engineered to keep the interconnect sufficiently transparent so that the perovskite and silicon subcells can harvest light efficiently. By balancing electrical recombination with optical clarity, the recombination layer avoids the trade-offs that typically force designers to choose between performance and manufacturability.

The results are striking. The researchers achieved power conversion efficiencies (PCEs) of 33.3% in 1.0-cm² perovskite/silicon tandem devices. More importantly for industrial translation, they scaled to an area of 207.87 cm² and still reached 30.6% PCE, indicating that the recombination layer concept tolerates the structural and processing complexity of large-area fabrication.

Operational durability also improved, supporting the claim that TiOxNy not only performs electrically but also stabilizes interfacial chemistry against the stresses that degrade tandem stacks. In practical terms, this suggests a path toward longer-lived, high-yield manufacturing rather than fragile, lab-only prototypes.

With indium-free materials and minimal optical penalty, TiOxNy could become a scalable interconnection choice for next-generation tandem photovoltaics. If further validated across manufacturing lines, it may help accelerate the move from record efficiencies toward technology that can be deployed widely.

Subject of Research: Perovskite/silicon tandem solar cells; recombination layers
Article Title: High-performance perovskite/silicon tandem solar cells enabled by multifunctional titanium oxynitride recombination layers.
Article References: Cao, F., Li, Y., Wang, S. et al. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02116-4
DOI: https://doi.org/10.1038/s41560-026-02116-4
Keywords: titanium oxynitride; TiOxNy; perovskite/silicon tandem; recombination layer; indium-free interconnect; self-assembled monolayers; SAM anchoring; operational stability

At the core of this innovative method lies the meticulous preparation of pre-patterned indium tin oxide (ITO)-coated glass substrates, which undergo rigorous cleaning treatments to ensure pristine surfaces. These substrates serve as the foundation upon which multidimensional deposition processes unfold. The use of a vacuum chamber integrated within a nitrogen-filled environment allows for the delicate sublimation of organic and inorganic precursors, thereby preventing unwanted degradation and contamination. Such a controlled atmosphere is essential for maintaining the intrinsic properties of the perovskite layers and the interfaces crucial for efficient charge extraction.

The detailed sublimation parameters are finely tuned: the organic charge transport materials, such as TaTm and C60, are deposited at rates ensuring thin, consistent layers that facilitate charge movement and reduce recombination losses. The P-doped hole transport layer, formed by co-sublimating the organic semiconductor TaTm with the dopant CS90112, is carefully controlled to balance conductivity and stability. Concurrently, the team applies an inorganic scaffold through CSS, composed of lead halide mixtures including PbI2 and PbBr2 in varying molar ratios. These scaffolds achieve thicknesses around 250 nm, crucial for optimal light absorption and carrier collection.

One of the distinctive features of this research is the custom-designed powder bed for organic precursors composed of methylammonium iodide (MAI) and methylammonium bromide (MABr). By mechanically blending these salts into homogeneous mixtures and conducting rigorous two-stage thermal tempering, the researchers ensure reproducible and stable source conditions. This methodical preparation guarantees that sublimation rates remain consistent across experimental rounds, thereby enhancing the reliability of the film growth and device results.

Recognizing the sensitivity of perovskite layers to environment and processing conditions, an elaborate pre-deposition conditioning protocol was instituted. This involved stabilizing the source and substrate plates through repeated heating cycles under low-pressure conditions, finely tuning the evaporation equilibrium before actual film deposition. Additionally, post-deposition thermal annealing is conducted in a controlled humidity atmosphere, further enhancing crystallinity and passivation of the perovskite films, which are critical for high photovoltaic performance and stability.

The team takes meticulous care in evaluating the effects of surface treatments such as dynamic washing with isopropanol. Interestingly, in their comprehensive analysis, they found that omitting the washing step does not adversely affect device efficiency, highlighting the robustness of the CSS process and the as-deposited film morphology. For defect passivation, an ethylene-diammonium di-iodide (EDAI2) layer is evaporated under high vacuum, enhancing interfacial quality and reducing nonradiative recombination pathways that inevitably handicap device performance.

Fabrication advances also extend to the tandem solar cells themselves. Silicon bottom cells, cleaned and prepared with precise sonicating and UV-ozone treatments, receive additional hole transport layers sputtered from nickel oxide targets. In particular, for textured silicon substrates, which offer increased light trapping, the deposition thicknesses are scaled up appropriately to ensure conformal coverage, a key factor in preserving device uniformity and efficiency. The replacement of bathocuproine (BCP) with atomic layer deposited (ALD) SnO2 as the buffer layer signifies innovation aimed at protecting underlying layers during transparent conductive oxide (TCO) deposition.

The ALD process highlighted involves an intricate balance between temperature settings and precursor pulsing, utilizing tetrakis(dimethylamino)tin (TDMASn) and water vapor for layer growth. The precise timing and sequence of precursor exposure and purging ensure the formation of uniform, pinhole-free SnO2 films critical for electrode protection and charge management. Additionally, sputtered indium zinc oxide (IZO) layers serve as transparent electrodes atop the devices, contributing both to electrical conductivity and optical transparency required for high overall device efficiency.

Characterization techniques reflect the rigor applied throughout the research. Current-voltage (J-V) measurements under standardized illumination conditions provide essential performance metrics, with careful consideration of scan rates, delay times, and mask-defined active areas to precisely quantify photovoltaic parameters. Tandem devices specifically employ class AAA LED-based solar simulators calibrated with certified reference cells, capturing the nuanced behavior of stacked devices under realistic operational conditions.

Complementing electrical evaluation, spectral response methods such as external quantum efficiency (EQE) elucidate wavelength-resolved photoresponse, with tailored optical biasing of sub-cells allowing for selective interrogation of perovskite and silicon layers. This level of spectral dissection affords insights into current matching and voltage losses, vital for optimizing tandem cell architectures. Suns-Voc measurements further dissect open-circuit voltage contributions from individual sub-cells, applying selective illumination to unravel recombination mechanisms and interface quality.

The research team deploys an arsenal of structural characterization tools to interrogate film quality and crystallinity. X-ray diffraction (XRD) and grazing incidence techniques, alongside grazing-incidence wide-angle X-ray scattering (GIWAXS), reveal crystallographic orientations, phase purity, and grain coherence, which are directly linked to optoelectronic properties. SEM imaging provides nanoscale morphological insights, while photoluminescence mapping and photocarrier grating measurements elucidate carrier dynamics, non-radiative recombination, and uniformity—factors crucial to predictive device modeling and scalability.

This comprehensive approach exemplifies how precise material synthesis, interface engineering, and rigorous characterization converge to push the frontier of perovskite/silicon tandem solar cells. By harnessing close-space sublimation, a technique known for its scalability and industrial compatibility, this research opens avenues for mass production of tandem photovoltaics with efficiencies that could surpass the limits of single-junction devices while remaining cost-effective.

Moreover, the integration of these devices on textured silicon substrates enhances light management and increases photogenerated current while maintaining compatibility with existing silicon manufacturing practices. This symbiotic relationship between novel perovskite materials and well-established silicon technology hints at a compelling future where high-performance, low-cost solar modules become accessible on a commercial scale.

The meticulous attention to source material preparation, deposition parameters, and post-processing ensures reproducibility—a critical attribute for transitioning from laboratory prototypes to industrial applications. The robustness of the CSS technique in tailoring material composition gradients and film thickness also promises customizability, enabling the fine-tuning of bandgaps necessary for optimized multi-junction cell architectures.

In conclusion, this breakthrough showcases close-space sublimation as not merely a fabrication step but a versatile platform enabling the assembly of complex perovskite/silicon tandem solar cells with reproducible, high-quality interfaces and outstanding photovoltaic performance. As the quest for sustainable and scalable solar energy solutions intensifies, such innovations are paramount in meeting global energy demands while reducing environmental footprint.

Subject of Research: Perovskite/silicon tandem solar cells fabricated via close-space sublimation deposition techniques.

Article Title: Close-space sublimation as a versatile deposition process for efficient perovskite silicon tandem solar cells.

Article References:
Diercks, A., Chozas-Barrientos, S., Gil-Escrig, L. et al. Close-space sublimation as a versatile deposition process for efficient perovskite silicon tandem solar cells. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02068-9

DOI: https://doi.org/10.1038/s41560-026-02068-9

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 implications of this research are monumental as global demand for renewable energy sources accelerates in tandem with the urgency to combat climate change. Perovskite/silicon TSC technology offers a beacon of hope with its potential to contribute significantly to the transition towards sustainable energy solutions. Despite their considerable promise, TSCs are grappling with ongoing challenges that need to be surmounted to transition from laboratory innovations to fully fledged commercial viability. The focus of the PolyU team, under the leadership of prominent experts—including Prof. Li Gang, Chair Professor of Energy Conversion Technology, and Prof. Yang Guang, Assistant Professor—revolves around conducting thorough analyses of TSC performance coupled with strategic recommendations aimed at improving the technology’s practicality.

Prof. Li Gang has emphasized that while initial lab-scale devices have showcased remarkable efficiency improvements, ensuring the reliability of these devices remains a paramount challenge. The efficiency loss when scaling from small-area devices to large commercial modules is particularly concerning, signaling the need for extensive research and validation before mass production can become a reality. Reliable manufacturing methods must not only uphold industrial standards but also adapt to the peculiarities of perovskite materials, enabling their integration into widespread use.

A major hurdle faced by researchers lies in the inherent instability of perovskite materials, which are sensitive to environmental conditions such as moisture, oxygen, ultraviolet light, and thermal fluctuations. These challenges pose considerable threats that hinder the performance and lifespan of the solar cells. Moreover, the transition from lab prototypes to commercially feasible solar modules requires an in-depth focus on achieving uniformity and robust defect control during large-area fabrications. The initial rounds of outdoor testing of perovskite/silicon TSCs have been promising but have generated few certified data regarding their long-term reliability, necessitating accelerated stability testing protocols grounded in established international standards.

The PolyU research team has also brought to light another layer of complexity regarding the materials used in current cell designs. Although the raw materials for perovskites are generally low-cost, the inclusion of rare elements and heavy metals, notably lead, resonates with environmental and regulatory concerns. A sustainable approach—including both the development of eco-friendly alternatives and efficient recycling or sequestration strategies—must be a focal point as the researchers work toward realizing commercialisation potential. This multi-faceted outlook aligns with broader environmental goals and regulatory frameworks that aim to minimize ecological footprints while maximizing energy yield.

Furthermore, the technological prowess exhibited by the PolyU research team is paving the way for groundbreaking collaborations between academia and industry. The researchers propose a comprehensive, multidisciplinary approach that interlinks material science, device engineering, and economic modeling. This synergy is essential to facilitate the advancements necessary for real-world applications, driving down costs while escalating efficiency levels of perovskite/silicon TSCs. Prof. Yang Guang has articulated that effectively addressing the scientific challenges faced is critical to reaching lower levelized electricity costs—an essential factor for broad adoption of renewable technologies across various sectors.

This commitment to collaboration stems from the pressing need to evolve our energy landscape in tandem with ongoing global shifts towards sustainability. The innovations surrounding perovskite/silicon TSCs dovetail excellently with the strategic goals of reducing carbon emissions and achieving carbon neutrality. The vision posited by the PolyU team resonates not only with energy producers but also with high-energy-consuming industries, including artificial intelligence, which increasingly demand clean, efficient power sources.

As prospects for this technology continue to unfold, the research team at PolyU remains resolute in their mission to overcome hurdles and ensure the transition of perovskite/silicon TSC technology from laboratory settings to viable commercial fabrication and deployment. The journey ahead is laden with challenges, yet the progress made thus far serves as a testament to human ingenuity in the pursuit of sustainable energy solutions. The work of Prof. Li, Prof. Yang, and their colleagues echoes the spirit of innovation that is pivotal for guiding the world towards a low-carbon future, fostering a generation of devices that not only meet but exceed current expectations in terms of power generation efficacy.

In the coming years, as we further explore and refine these technologies, the solar landscape stands to benefit immensely. The collaborative efforts at the Hong Kong Polytechnic University serve as a microcosm of what is achievable through science and innovation, making it clear that while challenges exist, the potential for compelling advancements in solar energy technology is vast. The work done here reflects a broader trend toward integrating advanced technology into renewable energy systems, ensuring that we harness the power of the sun more effectively—from the individual household level to large industrial applications, thus lighting the way towards a more sustainable and energy-efficient future.

Subject of Research: Development of perovskite/silicon tandem solar cells to enhance efficiency and commercial viability.

Article Title: Towards efficient, scalable and stable perovskite/silicon tandem solar cells

News Publication Date: 14-Aug-2025

Web References: Nature Photonics

References: DOI link: 10.1038/s41566-025-01732-y

Image Credits: Credit: polyu

Keywords

Solar energy, Perovskites, Silicon, Renewable energy, Artificial intelligence, Electrical engineering.

A recent breakthrough study spearheaded by a collaboration of researchers, including Fang, Ding, Yang, and colleagues, introduces an innovative dual-buffer-layer strategy designed to fundamentally address these mechanical challenges. This pioneering approach utilizes a composite buffer system comprising two distinct tin oxide (SnO_x) layers, each engineered with precise structural and functional characteristics to synergistically alleviate mechanical stress and preserve the electrical integrity essential for efficient charge extraction. Central to this design is the controlled modulation of the atomic layer deposition purging time, which tailors the microstructure of the buffer layers and thereby optimizes their stress dissipation and electrical contact capabilities.

The first component of this dual-buffer system is a deliberately engineered loose SnO_x layer. Characterized by a less dense structure, this layer operates as a strain energy dissipation medium, effectively cushioning the delicate interfaces from the recoiling forces induced during subsequent sputtering deposition processes. By absorbing and redistributing mechanical stresses generated during thermal and mechanical cycling, the loose SnO_x buffer acts as a protective cushion, substantially mitigating the risk of cracks and delamination that conventionally plague flexible solar modules under repeated bending and environmental fluctuations.

Complementing this stress-relieving cushion is a tightly packed, compact SnO_x layer optimally designed to ensure strong electrical contact and effective charge transport pathways. This dense layer maintains the critical electrical interfacial coupling between the perovskite absorber and silicon substrates, enabling sustained high carrier mobility and reducing recombination losses. The dual-buffer-layer construct cleverly balances mechanical flexibility with electronic functionality through this sequential layering, providing a durable yet high-performance interface previously unattainable in flexible tandem solar architectures.

Implemented on an ultrathin silicon bottom cell just 60 microns thick, this dual-buffer-layer strategy culminated in a flexible tandem solar cell boasting an extraordinary certified power conversion efficiency of 33.4% on a 1-cm^2 active region. Notably, when scaled up to a wafer-sized 260-cm^2 module, the device maintained a robust certified efficiency of 29.8%, demonstrating remarkable scalability without sacrificing performance. This feat underscores the potential for widespread commercial viability and integration into diverse form factors where lightweight and flexible power sources are paramount.

A defining strength of these advanced tandem cells extends beyond efficiency into their impressive power-per-weight ratio, reaching up to 1.77 W/g. This metric signals a transformative advancement for portable and aerospace photovoltaic applications, where maximizing energy output relative to mass is a critical criterion. The ultrathin silicon base combined with the mechanically resilient dual-buffer interface manifests in devices lightweight enough for emerging sectors without compromising electrical robustness.

Durability assessments further validated the mechanical and operational resilience conferred by the dual-buffer design. The flexible tandem cells retained over 97% of their initial performance metrics after enduring an arduous 43,000 bending cycles, executing these deformations with a minimum curvature radius of approximately 40 millimeters—conditions that far exceed everyday mechanical stress scenarios in wearable electronics. Such endurance signals a paradigm shift towards solar cells that can withstand repetitive strain without succumbing to failure modes that have hampered flexible photovoltaics historically.

Thermal stability likewise benefitted significantly, with the tandem solar cells exhibiting around 97% retention of original power conversion efficiency following 250 cycles of rigorous thermal fluctuations between -40 °C and 85 °C. This wide thermal endurance window simulates practical operating environments ranging from extreme cold to high heat, underscoring the buffer layers’ crucial role in mitigating thermal expansion mismatch and preventing interfacial cracking under such stresses.

This novel dual-buffer-layer engineering thus addresses a fundamental bottleneck in the flexible solar cell domain: the tradeoff between mechanical flexibility and functional stability. By strategically managing interfacial strain while solidifying electronic coupling, the approach bridges the gap between flexible form factor demands and the uncompromising efficiency standards of photovoltaic technologies reserved traditionally for rigid substrates.

The implications of these findings extend well beyond the laboratory. As the global community intensifies efforts for clean energy transition and portable power solutions, perovskite/silicon tandem solar cells equipped with robust stress mitigation mechanisms open avenues for integrated power sources in automotive, aerospace, wearable, and architectural applications. This technology promises not only enhanced energy yield but also mechanical resilience essential for the widespread adoption of flexible photovoltaics.

Looking ahead, the research team anticipates that further refinement in buffer layer material chemistry and deposition techniques could unlock even higher efficiency thresholds and durability milestones. Moreover, integrating this dual-buffer concept with evolving perovskite compositions and encapsulation strategies could amplify device longevity and environmental stability, propelling flexible tandem solar cells closer to mass-market realities.

This work stands as a landmark achievement, exemplifying how nuanced interface engineering grounded in atomic layer deposition dynamics can dramatically advance the field of sustainable energy materials. As the solar industry increasingly calls for adaptability, efficiency, and longevity, the dual-buffer-layer framework marks a critical step towards realizing durable, high-performance flexible photovoltaic platforms capable of powering a more sustainable and connected future.

Subject of Research: Development of mechanically robust, high-efficiency flexible perovskite/silicon tandem solar cells through innovative dual-buffer-layer interface engineering.

Article Title: Flexible perovskite/silicon tandem solar cell with a dual buffer layer.

Article References:
Fang, Z., Ding, L., Yang, Y. et al. Flexible perovskite/silicon tandem solar cell with a dual buffer layer. Nature (2025). https://doi.org/10.1038/s41586-025-09835-w

Image Credits: AI Generated