Perovskite solar cells (PSCs) hold great potential as technology for the next generation of thin-film photovoltaics. However, industrial-scale fabrication processes must be significantly improved for PSCs to become commercially viable. Scalable solution deposition techniques, such as slot-die(SD)-coating, are difficult to control during the entirety of the perovskite thin-film formation, because of complex fluidics, drying, and crystallization dynamics during high solvent removal. Drying with a narrow gas-purged slot-jet is an established drying method that provides a sufficiently high solvent mass transfer to remove the solvent from the wet thin-film, inducing a prompt nucleation. In prior studies, a model on drying dynamics of perovskite thin-films enhances the understanding of the complex drying process, analyzing impacts of gas-flow velocity and web speed from a fundamental view point^[1;2]. Moreover, we validated the model on large-area substrates, predicting drying windows by in-situ monitoring of SD-coated thin-film drying processes^[3]. The results lead to concrete rectification work on the drying procedure, enhancing the optimally dried area. However, slot-jet-drying still comes with inhomogeneous fluidic dynamics and disturbed gas flows, causing unintended fluidic backflows, non-uniform drying patterns and severe edge effects, impeding progress for perovskite/silicon tandem solar cells (TSCs). Hence, there is need to investigate and optimize the formation of polycrystalline perovskite thin-films fabricated via scalable deposition methods.

In response, we address the necessity for precise drying conditions, enhancing the quality of perovskite thin-films through i) a novel convection-drying method, advancing the homogeneity of the drying process of SD-coated solution thin-films on the entire area, and ii) an adjusted material composition strategy for 2-step processed SD-coating, leading to higher operational stability. Specifically, we introduce a gas-assisted-drying system that provides uniformly distributed drying rates for SD-coated, 2-step processed triple-halide perovskite wet thin-films. Precisely defined drying conditions are established using a stationary, gas flow-controlled two-dimensional nozzle array pattern, consisting of impinging jets and surrounded by suction holes for local solvent removal. This design enables precise control of drying rates. The specific drying system used in this work is inhabited in an in-house glovebox system, meaning the drying circle is fully integrated into the inert atmosphere.

We systematically evaluate and compare the implemented novel drying strategy with established slot-jet-drying by fabricating SD-coated PSCs with alternative drying approaches over an area of 100 cm² with all scalable techniques. Remarkably, we successfully demonstrate the correlation of applied process parameters at exact sample positions with the resulting thin-film morphology, grain size distribution, and optoelectronic properties, resulting in PSCs with efficiencies up to 19.6% and high PCE-yield of >90% on the entire substrate. We validate an enhanced area utilization with 5x5 cm² solar mini-modules on the quadrants of 10x10 cm² substrates, each reaching a PCE ≥17.6% (17.7% ±0.2%). The results imply high homogeneity during the coating and drying processes, with only minimal relative upscaling loss due to module scribing and interconnection resistances, outlining the relevance of our scaling methodology. Consequently, we employ the drying method to a material composition suitable for tandem applications (E_g ~1.68 eV) based on a work of Pappenberger et al^[4]. We demonstrate TSCs with PCEs of up to 24.6%, fabricated with all scalable techniques. Particularly, the successful fabrication of TSCs (mean PCE ~24.0%) with a homogeneous PCE distribution of ±0.7%, confirms the importance of a systematically controlled drying technique within an optimized 2-step process. This work underlines the necessity of precise control as well as an understanding of drying dynamics being vital to facilitate large-scale solution-based high-quality optoelectronic thin-films consistently.

Our full research paper“Spatially Regulated Gas Flow Control for Drying of Large Area Slot-Die-Coated Perovskite Thin-Films”by Kristina Geistert et al. is in preparation.