Perovskite–silicon tandem solar cells have become one of the most closely watched technologies in the race to increase the efficiency of commercial photovoltaics. By placing a light-absorbing perovskite layer on top of a conventional silicon cell, tandems can capture more of the solar spectrum than either material can use alone. Yet the technology faces a stubborn manufacturing problem: the solution-processing methods used to produce many high-performance devices can be difficult to scale uniformly across large areas and may introduce reliability concerns over the lifetime of a solar module.
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
