Pinhole-free Methylammonium Bismuth Iodide Perovskite Solar Cells Via All-Solution-Processed Multi-step Spin Coating

• Published in: Journal of Electronic Materials
• Main Author: Achoi M.F.; Noman M.A.A.; Kato S.; Kishi N.; Soga T.
• Format: Article
• Language: English
• Published: Springer 2022
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85119951272&doi=10.1007%2fs11664-021-09330-8&partnerID=40&md5=2c334ae49629fe19d6dbb2c1a3a4357b

In a functional solar cell device, the morphology of a layer is a key to the performance of Bi-based perovskite solar cells (Bi-PeSCs). Especially, pinholes generated during spin coating degrade the solar cell performance. This paper proposes a method to prepare pinhole-free methylammonium bismuth iodide (MBI) film by multi-step spin coating, with the thickness optimized by changing the layer number between 1 and 12 layers. A strong absorption band is observed at around the wavelength of ~ 500 nm for all the MBI layers. The scanning electron microscopy (SEM) cross-section images visually depict that the MBI layers are free from pinholes at more than 6 layers, and we found that the maximum solar cell performance was reached at 8 layers of MBI with an open-circuit voltage of 0.18V, which is greater than using a single-spin coating. After that, it exhibited a decrease in its performance by increasing the number of MBI layers. The growth model and its mechanism for pinhole-free multi-MBI layers is also discussed. These results suggested an improvement of MBI layer morphology in the development of solar cell devices in the future. Graphical Abstract: [Figure not available: see fulltext.]. © 2021, The Minerals, Metals & Materials Society.