Multiscale Characterization of Electrode-Induced Degradation in Perovskite Solar Cells

TL;DR

Researchers studied how perovskite solar cells degrade when stored in the dark, focusing on electrode corrosion and how to mitigate it.

Contribution

The paper introduces a multiscale characterization approach to identify and link electrode-induced degradation pathways to full-device performance.

Findings

Metal electrode corrosion causes Ag diffusion into the absorber and AgI formation, degrading perovskite domains.

ITO corrosion leads to voids and diffusion of In and Sn into the absorber when metal is absent.

Device stack modifications like SnOx and FTO can mitigate electrode-induced degradation.

Abstract

The stability of metal-halide-perovskite (MHP) solar
cells must
be understood and improved for the commercial viability of MHP technologies.
Here, we apply multiscale characterization methods to study degradation
modes, specifically electrode corrosion, for p-i-n MHP partial device
stacks and full devices that are stored in the dark under an inert
atmosphere. Our multiscale characterization approaches include full-device
electro-optical performance using current–voltage (JV) curves
and spatial imaging with electroluminescence (EL) and photoluminescence
(PL). We further correlate interface properties using cross-sectional
Kelvin probe force microscopy, which maps the nanoscale electric field
properties, and electron microscopy, which demonstrates structural
and chemical features. Devices stored as a full device stack degrade
primarily by metal (Ag) electrode diffusion into the absorber, with
formation of AgI byproducts and Ag accumulation near the indium tin
oxide (ITO) contact. This causes decomposition of the perovskite absorber
domains, loss of the potential drop at the electron transport layer
(ETL)/perovskite interface near the metal contact, and increased equivalent
resistance at the perovskite/hole transport layer (HTL) interface
near the ITO contact. The devices stored without metal show a different
degradation pathway dominated by corrosion of the ITO, creating voids
at the ITO electrode surface with diffusion of In and Sn into the
absorber. We conclude that metal electrode-induced degradation is
the most severe degradation pathway under dark storage, but that ITO
corrosion and absorber instability must also be mitigated. We further
demonstrate mitigation of these degradation pathways by changes to
the device stack, including a SnO
x
blocking
layer at the ETL side and replacing ITO with FTO at the HTL side.
These results provide a useful demonstration of specific dark degradation
pathways at each electrode interface, as well as a unique multiscale
example that links degradation of chemical, structural, and electrical
interface properties to the full-device electro-optical characteristics.

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