An open implementation of slot-die and blade coating operability limits for scalable perovskite photovoltaics

Abstract

Slot-die and blade coating deposit the functional layers of printed optoelectronic devices, and both fail outside a bounded region of process parameters. The boundaries of that region have been derived and measured since the 1940s, but the results are scattered across the coating-science literature in notation that differs between papers, and they are rarely applied by the materials groups who most need them. In practice, a laboratory establishes its coating window by trial and error, one substrate at a time, and the resulting knowledge stays tacit and local. We present pvcoat, an open-source Python package that computes wet and dry film thickness and the operability window for both coating heads directly from process parameters, implementing the low-flow limit, the coating-bead vacuum window, the Landau-Levich film thickness, and the air-entrainment speed together with the validity range each model was derived for. The package has no runtime dependencies, accepts quantities in the units coating practitioners use, and attaches an explicit warning to any result computed outside a model's range of derivation. We verify the implementation against seven closed-form identities, all satisfied to machine precision, and exercise it on a worked case representative of a formamidinium lead triiodide precursor ink. Two results of the framework deserve emphasis for practitioners. First, the low-flow limit rises as the two-thirds power of the capillary number, so increasing line speed makes thin films harder rather than easier: for the worked ink at a 100 μm gap, a 700 nm dry layer remains coatable only up to 106 mm s⁻¹, a factor of 31 below the air-entrainment ceiling of 3.31 m s⁻¹. Second, the speed at which a blade-coated film is thinnest is independent of solids loading, because the solids volume fraction cancels from both competing branches; diluting an ink lowers the whole thickness-speed curve without moving the crossover. We emphasize that pvcoat reproduces published equations and has not been validated against coating experiments, and we set out the validation program this requires. The package, its test suite, and the scripts reproducing every figure and table in this work are openly available under the MIT license.