Schematic illustration of conformal, oriented perovskite crystal structure deposited via co-evaporation on a micron-textured industrial standard Si wafer.
Researchers from the University of Oxford and the Hong Kong University of Science and Technology (HKUST) have developed a new way to make high-performance perovskite solar cells entirely without solvents, bringing the technology a step closer to large-scale industrial production.
Perovskite photovoltaics have attracted intense interest in recent years because of their rapidly rising efficiencies and potential for low-cost renewable electricity. Most of today’s highest-performing perovskite solar cells are produced from solution-based ‘inks’. In contrast, many established thin-film technologies – from OLED displays to optical coatings – are manufactured using vacuum deposition, a clean, solvent-free process that enables highly uniform coatings over large areas. However, perovskites made fully by vacuum deposition have so far suffered from poor crystal formation, leading to films that are more defect-prone and unstable under light and heat. Writing in Nature Materials, the Oxford–HKUST team report a breakthrough that overcomes this long-standing challenge.
Precise control over perovskite crystals
The researchers developed a multi-source thermal co-evaporation process that introduces lead chloride (PbCl₂) as an additional co-source during film growth. This subtle change allows precise control over how the perovskite crystals form and orient themselves.
Using this approach, the team produced a highly ordered wide-bandgap perovskite (1.67 eV) in which many of the crystal grains align in a favourable (100) ‘face-up’ orientation. This crystal structure is a hallmark of high-quality films and significantly improves resistance to light- and heat-driven degradation. As a result, the solar cells show enhanced optoelectronic performance and much stronger operational stability.
First certified performance for all-vacuum-deposited cell
With the new deposition method, the team achieved the first certified performance for an all-vacuum-deposited wide-bandgap perovskite solar cell. The devices reached a maximum-power-point-tracked power conversion efficiency of 18.35% on a 0.25cm² cell. In laboratory measurements, efficiencies of 19.3% were achieved, while larger 1cm² devices reached 18.5%.
Durability was tested using the International Summit on Organic Photovoltaic Stability (ISOS) protocols. Under the demanding ISOS-L-2 accelerated ageing test – full-spectrum, one-sun-equivalent illumination at 75 °C in air – encapsulated cells retained 80% of their peak performance after 1,080 hours.
‘Our work addresses the core materials-science problem that has held back vacuum-deposited perovskites,’ said lead author Xinyi Shen from the Department of Physics at the University of Oxford. ‘By engineering the evaporation process to control crystal orientation, we have achieved thermal and photostability on par with state-of-the-art solution-processed devices, while retaining all the advantages of a dry, industry-compatible vacuum technique.’
Seeing inside working solar cells
To understand how the devices behave during operation, the team employed operando hyperspectral imaging – an advanced technique that maps optical signals across a working solar cell with pixel-level resolution. Developed at HKUST, this method allowed the researchers to directly observe microscopic processes that influence long-term performance.
‘Leveraging operando hyperspectral imaging, we gained unprecedented spatiotemporal insights into the device physics,’ explained Professor Yen-Hung Lin. ‘We visualised and decoupled the processes of halide segregation and trap-mediated recombination at the microscopic scale, directly linking these features to macroscopic device performance.’
This analysis also distinguished beneficial radiative recombination from non-ideal loss pathways, providing a powerful diagnostic tool for future optimisation of perovskite devices.
Advancing perovskite-silicon tandem solar cells
High-quality vacuum-deposited perovskite layers are particularly valuable for tandem solar cells, where a perovskite top cell is stacked on a silicon bottom cell to capture more of the solar spectrum. Using their improved films, the researchers successfully coated industrial-standard silicon heterojunction cells with micron-scale surface texture.
The resulting perovskite-on-silicon tandem devices achieved efficiencies of 27.2% on 1cm² cells. In an outdoor trial in Italy, the all-vacuum-deposited tandem cells maintained around 80% of their initial performance after eight months of real-world operation, highlighting encouraging progress toward durable tandem photovoltaics.
‘This co-evaporation method is directly compatible with existing industrial thin-film deposition infrastructure,’ said Professor Henry Snaith of Oxford’s Department of Physics. ‘It transforms vacuum deposition from a compromised alternative into a frontrunner for producing high-performance, stable perovskite and tandem solar cells, offering a clear pathway from the lab to the factory floor.’
Crystal-facet-directed all-vacuum-deposited perovskite solar cells, X Shen et al, Nature Materials, 23 February 2026