What if perovskite solar cells could skip solvents and still deliver 27.2 percent efficiency? A vacuum process moves them closer to stable, large scale use.
Researchers from the University of Oxford and the Hong Kong University of Science and Technology HKUST have demonstrated a solvent free method to make perovskite solar cells, reporting a certified 18.35 percent efficiency for a wide bandgap device and 27.2 percent for a perovskite on silicon tandem. The process uses vacuum deposition instead of solution based inks and targets industrial scale manufacturing.
The team produced a 1.67 eV wide bandgap perovskite layer using vacuum processing and achieved a maximum power point tracked efficiency of 18.35 percent on a 0.25 cm² cell. Lab devices reached 19.3 percent, while 1 cm² cells delivered 18.5 percent. When integrated onto silicon heterojunction bottom cells, the tandem devices reached 27.2 percent efficiency on 1 cm² areas. In outdoor testing in Italy, the tandem cells retained about 80 percent of their initial performance after eight months of operation.
The process uses multi source thermal co evaporation with lead chloride PbCl₂ as an added evaporation source. This step improved control over crystal growth during film formation. The perovskite films showed grains aligned in a 100 face up orientation. This orientation is linked to optoelectronic performance and resistance to heat and light induced degradation.
Stability was tested under International Summit on Organic Photovoltaic Stability ISOS protocols. In the ISOS L 2 ageing test with full spectrum one sun illumination at 75 °C in air, encapsulated cells maintained 80 percent of their peak efficiency after 1,080 hours.
Perovskite photovoltaics have gained attention for efficiency gains and potential for low cost power. Most high efficiency devices use solution processing with precursor inks. Many thin film technologies such as OLED displays and optical coatings use vacuum deposition, a solvent free method that enables uniform coatings over large areas.
Fully vacuum deposited perovskites have faced limits in crystal growth, leading to defects and lower stability. The co evaporation method addresses this issue.
Perovskite layers are used in tandem solar cells, where a perovskite top cell is stacked on silicon to capture more of the solar spectrum. The results show that vacuum processing can deliver efficiency and operational stability for tandem solar modules.
