Tin dioxide (SnO₂) is commonly used as an electron transport layer in perovskite solar cells with nip architecture because of its good optical and electrical properties. However, SnO₂ dispersions that work well for spin‑coating are often not suitable for scalable deposition methods, especially roll‑to‑roll (R2R) compatible processes such as gravure printing. The main challenge is the rheology of the aqueous inks. Too low viscosity leads to strong ink spreading, poor edge definition, and loss of pattern accuracy during printing. [1]

In this work, we study SnO₂ ink formulation for scalable and R2R printing methods, with special focus on rheology control. Printing processes such as gravure printing require a certain type of rheology, and especially high viscosity is needed so that the printed pattern does not spread too much on the substrate. This is not critical for single cells, where large uniform areas are used, but it becomes essential for R2R fabricated modules. In serially interconnected solar modules, the sub-cell patterns are printed next to each other, and spreading of SnO₂ and poor edge accuracy can easily cause short circuits or loss of active area, and increase in the contact resistance in case the ITO electrode is covered by the overspread SnO₂. [1-3]

Two ink tuning strategies are investigated. The first one is based on solvent selection, where the solvent system is adjusted to increase viscosity for printing. The second strategy combines solvent tuning with an acid additive providing additional control on ink flow and spreading. Both approaches allow to modify the ink rheology by promoting the particle size growth.

Rheological measurements show that the optimized inks have suitable viscosity and shear‑thinning behaviour, which is beneficial for printing. High viscosity at rest helps to limit ink spreading after deposition, while lower viscosity under shear supports good ink transfer from the printing unit. With these inks, we obtain clearly improved printing quality with sharper SnO₂ film edges, minimized spreading and overall uniform printed patterns.

Gravure printed SnO₂ layers are used in perovskite solar cells, and the devices show better performance compared to reference cells made with non‑optimised inks. The results show that rheology, and especially viscosity, is a key parameter when moving SnO₂ deposition from lab‑scale methods to scalable R2R fabrication.