A new solvent-free vacuum deposition process could accelerate the industrialization of perovskite-silicon tandem cells, improving scalability, uniformity and manufacturing speed.
Perovskite-silicon tandem solar cells gain a new industrial manufacturing pathway
Perovskite-silicon tandem solar cells are widely considered one of the most promising technologies for pushing photovoltaic efficiency beyond the limits of conventional silicon modules. By combining a perovskite top layer with an underlying silicon cell, these devices can capture complementary portions of the solar spectrum more effectively.
The perovskite layer absorbs high-energy light, while silicon converts lower-energy wavelengths, enabling significantly higher overall solar conversion efficiency compared to single-junction technologies.
Yet despite the rapid progress achieved in laboratories, one major obstacle remains unresolved: large-scale industrial manufacturing. Producing thin, uniform perovskite layers quickly and consistently over textured silicon surfaces continues to be one of the sector’s most difficult technical challenges.
A new study published in the journal Nature Energy by researchers from the Karlsruhe Institute of Technology and the University of Valencia may now offer a viable solution.
A vacuum-based process that could reshape tandem solar manufacturing
The two research teams refined a technique known as Close-Space Sublimation (CSS), a vacuum-based process capable of depositing perovskite precursor materials directly onto silicon cells without the use of solvents.
The mechanism is relatively straightforward. The precursor materials evaporate and travel only a few millimeters before depositing onto the silicon surface, where they react to form the perovskite layer.
The advantages are significant from an industrial perspective. Conversion times were reduced to just 10 minutes, while material consumption per cycle remained low thanks to reusable source materials.
“For industrial production, efficiency alone is not enough. Speed, robustness and scalability are equally important,” explained Professor Ulrich Paetzold of KIT. “We demonstrated that an exceptionally fast vacuum process can not only produce uniform layers, but also efficient perovskite-silicon solar cells.”
Depositing perovskite layers onto microstructured silicon wafers has long represented a critical bottleneck for scalability. Achieving homogeneous films on non-planar geometries without defects, voids or local compositional variations remains extremely challenging.
Bromine chemistry enables precise band gap control
To achieve the required band gap, researchers also had to solve another issue. During the conversion process, bromine, the key element used to increase the band gap, tended to disperse.
The solution came through the chemistry of the organic precursors.
“By modifying the ratio between methylammonium iodide and methylammonium bromide in the organic sources, we were able to control the bromine content in the final material,” said Dr. Alexander Diercks of KIT, who worked on the project at the University of Valencia במסגרת the Horizon Europe Nexus programme.
Uniform perovskite layers on smooth and textured silicon surfaces
Another crucial factor for industrial scalability involves silicon surface morphology. High-efficiency solar cells frequently rely on textured surfaces featuring micro or nanostructures to extend the optical path of light and maximize absorption.
Many deposition methods, however, only work effectively on perfectly smooth surfaces.
The researchers tested the CSS sublimation process on three different silicon subcell configurations:
- Smooth surfaces
- Nanostructured surfaces
- Microstructured surfaces
The results showed uniform perovskite layers across all three surface types without requiring modifications to the process parameters.
Scanning electron microscopy analyses and X-ray measurements confirmed homogeneous surface coverage.
“A process that only works on perfectly smooth surfaces would have limited industrial relevance,” noted Professor Henk Bolink of the University of Valencia. “The fact that close-space sublimation can produce uniform layers even on textured silicon cells makes this approach highly relevant for practical implementation.”
What this means for the future of photovoltaics
The achieved efficiencies, ranging from 23.5% to 24.3%, are not record-breaking figures. State-of-the-art laboratory perovskite-silicon tandem cells already exceed 33% efficiency.
However, the most important outcome for the photovoltaic industry lies elsewhere. The study demonstrates that a rapid, solvent-free process compatible with standard industrial silicon surfaces can produce efficient tandem devices.
The remaining challenge is long-term operational stability. Bringing these cells to thousands of hours of real-world operation while maintaining high performance will likely become the decisive test before large-scale commercialization becomes viable.
