Substrate Topography Dictates Stability in Inorganic Perovskite Solar Cells

Nanoscale surface defects on patterned substrates act as primary triggers for rapid degradation in caesium lead iodide (CsPbI₃) films. This finding isolates a critical failure mode in the fabrication of inorganic perovskite solar cells, preventing the successful deployment of these materials in next-generation tandem photovoltaic devices. The immediate utility is clear: manufacturers must abandon standard laser patterning for this material class in favour of smoother etching techniques.

The Stability Bottleneck in Inorganic Perovskite Solar Cells

CsPbI₃ offers an optimal bandgap for tandem solar applications, pairing efficiently with silicon. However, the material suffers from extreme structural fragility. Engineers frequently observe immediate degradation when depositing the active layer onto patterned indium tin oxide (ITO). The material reverts to its non-functional, yellow δ-phase almost instantly during film formation. Previous assumptions often blamed chemical interactions or ambient moisture. This study shifts the focus to physical topography. The substrate itself forces the failure. The measured data indicates that stability is not solely a chemical equation but a geometric one.

Diagnosing the Surface Trigger

To isolate the cause, the research team compared two distinct patterning methods: laser-scribing and chemical etching. They employed scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and confocal microscopy to map the degradation sites. The difference proved stark. Chemically etched surfaces maintained film integrity. Laser-patterned surfaces did not. The imagery specifically pinpointed the degradation origin points at the laser-formed terminations. While the bulk of the film might remain temporarily stable, the edges failed immediately.

How Topography Drives Phase Transition

The degradation mechanism is physical. The study measured surface steps and microcrater edges created by the laser process. These features, mere 50 nanometres in height, disrupt the film growth. At these edges, the CsPbI₃ film undergoes localized δ-phase formation. The physical step creates a stress point. This stress alters thermal and structural behaviour, leading to recrystallization and grain coarsening in the affected zones. Essentially, the perovskite crystal cannot maintain its cubic structure when forced over these microscopic ridges. The structural mismatch acts as a seed. Once the δ-phase nucleates at the edge, it propagates, compromising the entire device.

Implications for Device Fabrication

This intelligence dictates a shift in manufacturing protocols. Standard laser patterning, while fast, introduces fatal defects for inorganic perovskites. The measured data suggests that substrate smoothness is not merely cosmetic but functionally vital. To secure high-efficiency inorganic perovskite solar cells, manufacturers must adopt gentler patterning techniques like chemical etching or develop post-processing steps to smooth laser-scribed edges. Eliminating 50nm ridges could stabilise the production yield of tandem Si/perovskite modules. This insight moves the field past trial-and-error chemistry toward precise substrate engineering.