Publication date: 15th December 2025
Due to their favorable band gap, photovoltaic devices based on inorganic perovskites, such as CsPbI3, are of great interest. Most photovoltaic applications require the deposition of an active perovskite layer several hundred nanometres thick on structured indium tin oxide (ITO) layers. However, depositing CsPbI3 on structured ITO often causes a phase transition from perovskite, which is localised at the border between conductive ITO and glass, to the non-perovskite δ-phase. In our study, we investigate the impact of substrate topography on the high-temperature stability of the perovskite phase.
By comparing ITO structuring methods (i.e. laser structuring and chemical etching), we demonstrate that perovskite degradation consistently begins at the ITO/glass border on laser-patterned substrates. Scanning electron microscopy, electron backscatter diffraction and confocal microscopy reveal significant local differences at the ITO/glass border for chemically treated and laser-ablated ITO. These differences were recreated using laboratory patterning experiments, showing that CsPbI3 strictly degrades on the lab-patterned ITO in line with the trend previously observed for commercial patterned ITO substrates. Disentangling the structural and topographical differences at the ITO/glass interface showed that the local ITO structure and grain size do not affect the perovskite layer. However, steep surface steps of at least 50–100 nm in height, particularly at the edges of laser microcraters, are sufficient to trigger the localised formation of the δ phase at the β-CsPbI3 formation temperature. This effect sporadically occurs on mechanically damaged substrates; however, it disappears at micrometer-sized scratches, regardless of slope steepness. Thus, it manifests when the topographical detail is comparable to the perovskite grain size.
Rather than offering a device-level optimization strategy, our study provides a visual and mechanistic understanding of how substrate geometry influences phase instability during film growth. This knowledge paves the way for substrate design strategies that suppress phase instabilities arising during the fabrication of perovskite-based inorganic optoelectronic devices.
This work was supported by the M-ERA.NET grant “PHANTASTIC” call 2021 [F-0129525-751-0E0-1020404]. The authors thank Prof. Dr. Andrés Fabián Lasagni for providing the microscope to perform the confocal measurements.
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