Perovskite solar cells (PSCs) represent a third-generation solar cell technology and a promising alternative to traditional photovoltaic technologies. One of the key advantages of this technology is solution processability which enables fabrication on flexible substrates using roll-to-roll (R2R) applicable methods such as slot die coating, gravure printing, and rotary screen printing. R2R manufacturing methods offer significant advantages in terms of material utilization and production speed, making them ideal for large-scale, portable, wearable and other applications where lightweight and flexibility are essential [1, 2, 3, 4].

The commercialization of PSCs hinges on the development of scalable, low-temperature, and solution-processable materials compatible with high-throughput R2R fabrication techniques. The R2R manufacturing methods require specific ink compositions and rheological properties, which our research has addressed previously. Tin dioxide (SnO₂) is a leading candidate for the electron transport layer (ETL) in PSCs due to its excellent electronic properties, transparency, and chemical robustness. Yet conventional colloidal SnO₂ dispersions designed for laboratoryspin‑coating translate poorly to industrial processes because of inadequate viscosity which causes uncontrollable ink spreading. We have demonstrated that transferring SnO2 deposition from laboratory to larger scale is achievable through ink formulation [2].

In this work, we present the development of a R2R-compatible SnO₂ ink for gravure printing. The formulation is based on a solvent blend containing water and alcohol. Alcohol is introduced as a rheology modifier to ensure suitable particle size distribution and viscosity leading to shear-thinning behavior that ensures clean ink release from the gravure cells and prevents ink bleeding after printing. This resulted in uniform deposition and film formation at low annealing temperatures (<140 °C) in ambient conditions, suitable for flexible substrates. The resulting SnO₂ layers demonstrate high optical quality, low surface roughness, and compatibility with perovskite absorbers. Devices fabricated using R2R printed SnO₂ ETLs in an n-i-p architecture with printed perovskite layer achieved power conversion efficiencies up to 11 % with excellent reproducibility and operational stability under continuous illumination (nearly 10 % PCE). This work highlights the importance of ink rheology and process compatibility in transitioning PSCs toward industrial-scale production via roll-to-roll manufacturing.