High Reproducible Fabrication of Perovskite Solar Cells using an Automated Perovskite Film Coating System

Perovskite solar cells are expected to be the next generation of solar cells due to their favorable characteristics such as high conversion efficiency, light construction, and flexibility. However, there are considerable variations in perovskite solar cell’s performances even though the solar cells are fabricated under the same conditions. Consequently, when evaluating new materials or new processes, it is necessary to fabricate many devices for comparing them with considering the large variations. This can be related to both cost increasing and time consuming for R&D.<br/><br/>One of the reasons for the variability in the performance of perovskite solar cells is the sensitivity of crystal growth in the perovskite layer to environmental factors such as temperature, humidity, and solvent evaporation rate. It is well known that these environmental factors influence the morphology of the film, making it important to control the atmosphere during deposition processes.^1–3 In addition, the widely used anti-solvent method for fabricating high-efficiency perovskite solar cells can cause significant changes in the film morphology and the solar cell performances based on the factors such as the drop volume, timing, and drop rate of the poor solvent. As a result, even when perovskite solar cells are fabricated under consistent conditions, their performances are still variable. In particular, the manual dropping of the poor solvent during the spin-coating of the perovskite precursor solution by human hands induces slight variations in the drop timing or drop speed, which leads to variations in the solar cell performances.<br/><br/>In this study, the low reproducibility, which is one of the challenges for perovskite solar cells, was improved by automating the dropping process of poor solvents and substrate transfer during the coating of perovskite layer. To remove human involvement in the perovskite layer coating process, an automated coating system was developed by integrating a robotic arm with a spin coater, an automatic solution drop system and a hot plate. This system enabled the transfer of glass substrates, the dropping of poor solvents during spin coating, and the heating of substrates on the hot plate. Using this automated coating system, we evaluated the performance variations of perovskite solar cells and compared them to those fabricated manually. The results showed that the perovskite solar cells fabricated using the automated coating system had reduced standard deviation of photoelectric conversion efficiency from 0.61 to 0.40 compared to those fabricated by hand. This system is expected to enable more objective evaluation of new materials and new processes, leading to reduced development time and costs.<br/><br/>References<br/>(1) Zhang, W.; Xiong, J.; Li, J.; Daoud, W. A. Impact of Temperature-Dependent Hydration Water on Perovskite Solar Cells. <i>Sol. RRL</i> <b>2020</b>, <i>4</i> (1), 1900370.<br/>(2) Bass, K. K.; McAnally, R. E.; Zhou, S.; Djurovich, P. I.; Thompson, M. E.; Melot, B. C. Influence of Moisture on the Preparation, Crystal Structure, and Photophysical Properties of Organohalide Perovskites. <i>Chem. Commun.</i> <b>2014</b>, <i>50</i> (99), 15819–15822.<br/>(3) Lin, N.; Qiao, J.; Dong, H.; Ma, F.; Wang, L. Morphology-Controlled CH3NH3PbI3 Films by Hexane-Assisted One-Step Solution Deposition for Hybrid Perovskite Mesoscopic Solar Cells with High Reproductivity. <i>J. Mater. Chem. A</i> <b>2015</b>, <i>3</i> (45), 22839–22845.