目的 提高风刀辅助下的钙钛矿前驱体中溶剂大面积蒸发的均匀性。方法 基于有限体积方法,耦合Hertz-Knudsen-Schrage蒸发方程,建立钙钛矿前驱体中溶剂二甲基甲酰胺（DMF）蒸发的计算流体力学（CFD）模型。首先得出DMF在热辅助蒸发过程中的蒸发冷凝系数,检验其独立性。然后在二维模型中引入风刀,研究风刀的吹扫角度、出口风速、距离液膜高度等因素对DMF蒸发通量均匀性的影响,探究了风刀辅助下的溶剂蒸发动力学。再将二维均匀性较好的风刀工况运用于三维模拟,探究风刀出口风速的振幅对蒸发均匀性的影响。结果 当蒸发冷凝系数值为1.12×10-4时,不同温度下的DMF蒸发通量的模拟值与实验值具有较好的一致性,表明蒸发冷凝系数具有独立性,不随温度、压力发生变化。风刀辅助液膜蒸发时,平行液膜表面速度大的区域蒸发通量高,在风刀吹扫角度40°、出口速度10 m/s、距离液膜高度10 mm;角度50°,风速10 m/s,距离5 mm;角度60°,风速5 m/s,距离10 mm,风刀正下方区域蒸发通量高且均匀性好,低振幅风刀出口风速能提高大面积衬底上的溶剂蒸发均匀性。结论 合适的风刀使用工况能使得液膜表面流速以均匀的层流形式分布,进而提高溶剂蒸发的均匀性,本研究的数值模拟方法能为实验提供指导价值。
Abstract
The work aims to improve the uniformity of large-scale solvent evaporation in perovskite precursors assisted by air knife (AK). A computational fluid dynamics (CFD) model was developed based on the finite volume method, coupled with the Hertz-Knudsen-Schrage evaporation equation, to investigate the evaporation kinetics of dimethylformamide (DMF) in perovskite precursors. Firstly, the thermal-assisted evaporation flux of DMF at different substrate temperatures was experimentally measured, and a two-dimensional model was established based on these experimental conditions. At a substrate temperature of 333.15 K, the evaporation-condensation coefficient in the evaporation equation was adjusted to align the simulated values with the experimental data. The accuracy of this coefficient was verified by comparing the flux values of simulated DMF evaporation at various temperatures with the corresponding experimental values. The results demonstrated excellent agreement among the experimental, simulated, and literature values. Furthermore, it was confirmed that the evaporation-condensation coefficient remained constant across variations in temperature and pressure, with a determined value of 1.12×10-4. Next, an AK was incorporated into the two-dimensional evaporation model to systematically investigate the effects of key parameters, including the blowing angle, outlet speed, and distance from the liquid film, on the uniformity of DMF evaporation flux. By analyzing the velocity distribution on the liquid film surface and the DMF partial pressure distribution, it was observed that the AK effectively removed solvent molecules from the liquid film surface, reduced the DMF partial pressure, and ultimately enhanced the evaporation flux. These findings validated the mechanism of AK-assisted solvent evaporation. Selecting appropriate operating conditions for the AK was critical to ensuring uniform laminar flow on the liquid film surface, thereby improving the uniformity of solvent evaporation. The optimized two-dimensional AK conditions were applied to three-dimensional simulations, including a blowing angle of 40°, an outlet velocity of 10 m/s, and a distance of 10 mm from the liquid film height. Additional conditions, such as a blowing angle of 50°, an outlet velocity of 10 m/s, and a distance of 5 mm, as well as a blowing angle of 60°, an outlet velocity of 5 m/s, and a distance of 10 mm, were also tested. The results revealed that the evaporation flux directly below the AK was high and uniform, while the surface velocity of the liquid film downstream of the AK decreased, leading to a reduction in evaporation flux on both sides. In practical production, maintaining a uniform outlet speed at the AK outlet is challenging. Therefore, the effect of outlet speed amplitude at the AK outlet on the uniformity of solvent evaporation across large-area substrates is investigated. The horizontal evaporation flux distribution shows a gradual decrease from directly below the AK to the sides, with larger outlet speed amplitudes resulting in greater flux non-uniformity. Specifically, at outlet speed amplitudes of 0, 1, 3, and 5, the widths of the regions where the longitudinal evaporation flux varies within 10% are 22 mm, 18 mm, 11 mm, and 7 mm, respectively. These results highlight the importance of controlling outlet velocity uniformity, providing methodological guidance from a numerical simulation perspective for achieving stable solvent evaporation in large-scale perovskite precursor fabrication.
关键词
钙钛矿太阳能电池 /
蒸发动力学 /
蒸发冷凝系数 /
均匀性 /
风刀 /
计算流体力学
Key words
perovskite solar cells /
evaporation dynamics /
evaporation and condensation coefficient /
uniformity /
air knife /
computational fluid dynamics
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基金
国家自然科学基金项目（22078091）; 上海浦江人才计划项目（2022PJD016）
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