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.

Wide-bandgap perovskites, especially all-inorganic compositions such as cesium lead iodide bromide (CsPbI₂Br), are prized for their suitability as top-cell materials in tandem solar cells. Their larger bandgaps improve photovoltage and tandem efficiency, yet their practical implementation is vexed by issues including uncontrolled crystallization processes, abundant defect states, energetic misalignment at interfaces, and phase instability. These problems tend to originate predominantly at the critical interface where the perovskite layer contacts the underlying electron transport layer, frequently a tin oxide-based material.

Tin oxide (SnO₂) has emerged as a popular electron transport layer due to its optical transparency, high electron mobility, and thermal stability. However, when utilized in its conventional alkaline-based solution-processed form, SnO₂ often induces deleterious effects to the overlying perovskite film. The alkaline environment disrupts stoichiometry and crystallization dynamics, promoting defect formation and undesirable phase transformations. These interfacial imperfections exacerbate non-radiative recombination and voltage losses, ultimately dampening device performance and operational durability.

To overcome these hurdles, the authors crafted an innovative bottom interface modulation approach by synthesizing acidic magnesium-doped tin oxide quantum dots. This acidic nanomaterial sculpted a more benign and optimized contact surface conducive to the nucleation and growth of high-quality CsPbI₂Br thin films. Unlike traditional alkaline SnO₂, this magnesium-doped variant delicately balances the physical, chemical, structural, and energetic properties of the interface. This synergy results in profound passivation of trap states, significantly reducing carrier recombination pathways.

The magnesium doping not only adjusts the acidity of the quantum dot dispersion but concurrently fine-tunes the energy band alignment between the electron transport layer and the wide-bandgap perovskite. This precise energetic matching facilitates efficient electron extraction and minimizes energy losses at the interface. Furthermore, the controlled acidic environment promotes uniform perovskite film morphology with larger grain sizes and fewer pinholes, key factors that support enhanced charge transport and suppression of defect proliferation.

Delving deeper into the instability mechanisms previously encountered with alkaline-based tin oxide contacts, the study reveals that the basic nature of the conventional SnO₂ solution provokes deleterious chemical interactions at the interface. These reactions destabilize the CsPbI₂Br lattice and trigger phase transitions that deteriorate device longevity. By contrast, the acidic magnesium-doped SnO₂ quantum dots not only foster superior initial film quality but also fortify the structural integrity against environmental and operational stresses.

Performance metrics cement the remarkable improvements afforded by this bottom contact engineering innovation. The standalone wide-bandgap CsPbI₂Br perovskite solar cell achieves a striking power conversion efficiency of 19.2% alongside a high open-circuit voltage (V_oc) of 1.44 V, exemplifying substantial reduction in voltage losses. This milestone embodies a significant leap over prior records hampered by interfacial defects and instability.

Extending this advancement to the tandem format, the researchers seamlessly integrated the improved inorganic top cell with an optimized organic bottom cell, yielding a monolithic perovskite/organic tandem solar cell exhibiting an impressive efficiency of 25.9%, certified at 25.1%. This achievement ranks among the highest certified efficiencies reported for perovskite-based tandems and signals a promising future for these hybrid photovoltaic platforms.

Beyond sheer efficiency, the tandem device manifests enhanced long-term stability under diverse environmental conditions, spanning thermal, humid, and illumination stress tests. Such robustness is critical for transitioning laboratory innovations into real-world applications, where operational durability remains a primary concern.

The authors’ work exemplifies the transformative impact of interface chemistry and nanoscale material engineering on next-generation photovoltaic technologies. By challenging conventional electron transport layer paradigms and introducing a finely tuned acidic magnesium-doped SnO₂ quantum dot system, the research community gains a potent toolkit to tackle persistent instability and performance bottlenecks inherent to wide-bandgap perovskite devices.

This bottom contact modulation strategy not only signals a promising route to push power conversion efficiencies closer to their theoretical maxima but also invigorates tandem solar cell architectures with the stability and performance reliability necessary for commercialization. Given the ongoing quest for cost-effective, high-efficiency solar energy conversion, these findings resonate broadly across academia and industry, attracting attention from materials scientists, chemists, and photovoltaic engineers alike.

Moreover, the study provides a compelling mechanistic framework elucidating how subtle shifts in solution pH and quantum dot doping radically alter interfacial interactions, crystallization kinetics, and energetic alignments. Such insights will undoubtedly spur further exploration into tailored interface materials and nanoscale design strategies to address analogous challenges in other optoelectronic devices.

In summary, the research by Han et al. delivers an elegant and effective solution to one of the most pressing challenges in wide-bandgap perovskite solar cells. The use of acidic magnesium-doped SnO₂ quantum dots as a bottom contact modulator achieves a harmonious balance of chemical compatibility, structural optimization, and energy band alignment. This balance yields perovskite films with reduced defects, enhanced stability, and superior photovoltaic performance.

The resultant high-efficiency tandem device, combining the merits of inorganic perovskites with organic photovoltaics, underscores the versatile potential of hybrid architectures. As the solar industry strives for sustainable, efficient energy solutions, such scientific breakthroughs offer compelling pathways toward scalable, durable, and high-performing solar cells.

Looking ahead, the interface engineering paradigm illustrated here opens avenues for integrating other dopants and fine-tuning interface acidity/basicity to engineer bespoke electron transport layers tailored for diverse perovskite and tandem compositions. This flexible approach promises to accelerate the development of commercial-grade solar cells capable of meeting global energy demands with improved cost-effectiveness and reliability.

In essence, this study not only advances the state-of-the-art of perovskite and tandem photovoltaics but also enriches our fundamental understanding of interfacial chemistry in complex optoelectronic systems. The successful implementation of this bottom contact modulation strategy represents a major stride toward realizing the full potential of wide-bandgap perovskites in next-generation solar energy technologies.

Subject of Research: Interface engineering in wide-bandgap cesium lead halide perovskite solar cells and perovskite/organic tandem photovoltaics.

Article Title: Inorganic perovskite/organic tandem solar cells with 25.1% certified efficiency via bottom contact modulation.

Article References:
Han, Y., Fu, J., Ren, Z. et al. Inorganic perovskite/organic tandem solar cells with 25.1% certified efficiency via bottom contact modulation. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01742-8

Image Credits: AI Generated

The effects of high-energy radiation, such as gamma rays from isotopes like cobalt-60 and cesium-137, have been a focal point for scientists aiming to assess the radiation hardness of perovskite materials. The operational environment of space—characterized by an oxygen and moisture vacuum—promises longevity for perovskite solar cells, which underscores their potential for long-term use in orbital stations and spacecraft. However, the challenge persists regarding the impact of total ionizing dose (TID) on these materials, as accumulated doses can range significantly, affecting performance over time. It is critical for researchers to establish a reliable understanding of how these materials behave under prolonged doses of radiation, paving the way for advancements in space-based energy systems.

In a recent publication in the prestigious journal, "Light: Science & Application," a research group led by Dr. Aleksandra Boldyreva from the Skolkovo Institute of Science and Technology took a significant leap in assessing the gamma-ray stability of a wide bandgap perovskite, which has a bandgap of 1.75 eV. This particular study revealed key insights into how small doses of gamma radiation, up to 10 kGy, can lead to passivation of certain negatively charged defects within perovskite films while simultaneously activating other intrinsic defects. Notably, admittance spectroscopy played a pivotal role, revealing that defects with an energy level of approximately 0.5 eV in the perovskite films demonstrated a remarkable decrease in concentration with increased gamma radiation exposure.

Furthermore, the diffusion coefficient—a measure of how quickly defects move within the material—increased significantly, by two orders of magnitude, after exposure to 6 kGy of radiation. This behavior is anomalous compared to typical Schottky-type defects, which usually see an increase in diffusion with an increase in their concentration. The peculiarity of this observation highlights the unique interactions between gamma radiation and the structural integrity of perovskite materials, indicating a complex mechanism at play that warrants deeper investigation.

As further gamma-ray doses were accumulated, the study observed a saturation effect in both the defect concentration and the diffusion coefficient. This surprising trend hints at intricate interactions between radiation and the defect dynamics within perovskite structures. Specifically, interactions at photon energies of 662 keV enforce the photoelectric effect, wherein electrons become excited by gamma photons, leading to vacancies or unrecombined holes left behind. As the presence of interfacial defects becomes prominent, gamma interactions result in a reduction of non-radiative recombination, a critical aspect for optimizing the efficiency of solar cells.

The study elucidates that an elevation in newly formed defects, as a byproduct of gamma exposure, leads to a tipping point where further radiation results in material degradation and a shift towards non-radiative recombination. This balance between defect passivation and introduction of new defects is central to developing robust perovskite materials capable of withstanding the rigors of space environments. The nuanced understanding of defect dynamics not only adds layers to the existing body of knowledge but also reshapes directions for future research focused on materials for space applications.

To better visualize the effect of gamma radiation, the researchers conducted analyses on fresh and exposed perovskite solar cells using annular dark-field scanning transmission electron microscopy (HAADF-STEM). The findings indicated a significant difference in iodine distribution between the exposed and unexposed samples, suggesting that radiation exposure can alter the elemental makeup and possibly the electronic properties of the perovskite structure.

The dominant defects identified were iodine vacancies, denoted as V, which saw a marked decrease in concentration with exposure to gamma rays. The research highlighted that this reduction aligns with the observed increase in the diffusion coefficient, pointing towards a migration mechanism through freshly created defects. This understanding is crucial, especially for the design of new perovskite compositions that could enhance performance while promoting stability under radiation conditions akin to space.