Organometallic halide perovskite has attracted extensive interest by virtue of its stunning defect tolerance, small excitonbinding energy, [1] high absorption coefficient, [2] extremely low trap-state density, [3] and long carrier diffusion length. [4] In just a few years, the power conversion efficiency (PCE) of lab-scale perovskite solar cells (PSCs) has swiftly skyrocketed from 3.8% to 25.2%, [5] outperforming all other thin film solar cells. Nevertheless, for the highest efficiency devices, all functional layers except the evaporated metal electrodes were fabricated by a non-scalable spin coating process. Thus, fabricating large-area high-efficiency PSCs remains challenging, and it is therefore imperative to develop continuous, large-area deposition processes for potential scalable production. To address this issue, quite a few potentially scalable techniques, such as spray deposition, [6] inkjet printing, [7] brush-painting deposition, [8] blade coating, [9] and slot-die coating [10] have been exploited in support of producing PSCs via low-temperature solution processes. Among them, slot-die coating is the most competitive because of its ability to precisely control largearea uniformity at the desired thinness of ≈500 nm with welldefined edges as required by module design. Additionally, high material utilization is another aspect of its attractiveness. In 2015, Hwang et al. ventured to deposit PbI 2 films via slot-die coating and then convert them to perovskites through methylammonium iodide solution immersion. [11] Kim et al. further optimized this method by inhibiting PbI 2 crystallization and increased the PCE to 18.3%. [12] This deposition/ conversion strategy can indeed increase the controllability of slot-die coating and decrease the operational difficulty. However, it suffers from incomplete material conversion and a high percentage of soaking solution wastage, which are incompatible with practical large-scale fabrication. Therefore, attention has increasingly turned to the one-step slot-die coating technique, [13] but it usually produces a rough perovskite layer with poor surface coverage because its demand for fast evaporation of solvent is not always assured as in the spin-coating process. To compensate for this drawback, substrate heating, anti-solvent engineering, and gas treatment were established Slot-die coating holds advantages over other large-scale technologies thanks to its potential for well-controlled, high-throughput, continuous roll-to-roll fabrication. Unfortunately, it is challenging to control thin.film uniformity over a large area while maintaining crystallization quality. Herein, by using a high-pressure nitrogen-extraction (HPNE) strategy to assist crystallization, a wide processing window in the well-controlled printing process for preparing high-quality perovskites is achieved. The yellow-phase perovskite generated by the HPNE acts as a crucial intermediate phase to produce large-area high-quality perovskite film. Furthermore, an ionic liquid is developed to passivate the perov...
