# Hidden Triggers of Degradation during Fabrication of Inorganic Perovskite Solar Cells

## TL;DR

This paper explains how tiny surface features on ITO substrates cause degradation in inorganic perovskite solar cells during fabrication.

## Contribution

The study reveals that nanoscale surface steps and microcrater edges on patterned ITO trigger perovskite degradation.

## Key findings

- Perovskite degradation initiates at laser-formed ITO terminations.
- Nanoscale surface features as small as 50 nm can trigger δ-phase formation.
- Localized δ-phase regions show distinct thermal and structural behavior.

## Abstract

Photovoltaic devices
based on inorganic perovskites, such as CsPbI3, are of
great interest for applications, either as a single-junction
or in Si/perovskite tandem devices due to their favorable bandgap.
Such applications often require the deposition of the perovskite active
layer on patterned indium tin oxide (ITO) layers. Yet, in many instances,
the deposition of CsPbI3 on structured ITO leads to the
almost instantaneous degradation of the perovskite layer during film
formation. In this work, we demonstrate how the microstructural and
topographical features of patterned ITO substrates influence the degradation
of CsPbI3 into its nonperovskite δ-phase. By comparing
two methods for patterning ITO, i.e., laser-patterning and chemical
etching, we demonstrate that perovskite degradation consistently initiates
at laser-formed terminations. We utilize scanning electron microscopy,
electron backscatter diffraction, and confocal microscopy to prove
that even nanoscale surface steps and microcrater edges, approximately
50 nm in height, are sufficient to trigger localized δ-phase
formation. These regions exhibit distinct thermal and structural behavior,
including recrystallization and grain coarsening. Our study provides
a mechanistic understanding of how substrate morphology drives phase
instability during film growth, paving the way for substrate engineering
strategies to suppress phase instabilities that occur during the fabrication
of inorganic perovskite-based optoelectronic devices.