# Impact of Argon, Nitrogen, and Oxygen Exposure on the Structural and Optoelectrical Properties of Mixed Tin–Lead Halide Perovskites

## TL;DR

This study examines how argon, nitrogen, and oxygen affect the stability and performance of tin-lead halide perovskites used in solar cells.

## Contribution

The study reveals how different gas environments influence carrier trapping and material stability in mixed tin–lead halide perovskites.

## Key findings

- Carrier trapping increases significantly when perovskites are exposed to nitrogen and oxygen.
- Fast photocurrent decay is linked to spatial traps at perovskite boundaries, reducing carrier mobility.
- Environmental conditions during fabrication and storage critically affect material stability and charge dynamics.

## Abstract

Mixed tin–lead halide perovskites are considered
promising
materials for narrow-bandgap photovoltaic applications, particularly
in tandem solar cells. However, their practical implementation is
hindered by stability issues, especially due to tin oxidation and
trap-state formation. In this study, we investigate the impact of
argon, nitrogen, and oxygen storage environments on the structural,
optical, and electronic properties of mixed tin–lead halide
CsFAPb0.5Sn0.5I3 perovskites. Optical
absorption, transient photoluminescence (PL), transient photocurrent,
and time-delayed collection field (TDCF) measurements reveal the significant
role of environmental conditions on carrier dynamics. Carrier trapping
over tens of nanoseconds is observed in samples prepared and stored
in argon, with a trapping rate increasing several times after exposure
to nitrogen (with less than 0.1 ppm of oxygen) and further increasing
upon exposure to O2. Photocurrent transients also show
a fast photocurrent decay component occurring within tens of nanoseconds,
independent of the oxygen-created traps. Based on the TDCF measurements,
we attribute this fast photocurrent decay component to the spatial
traps created by the perovskite boundaries, which reduce the carrier
mobility to values below 0.05 cm2/V·s, as estimated
from transient photocurrent measurements. Our findings highlight the
importance of carefully controlling fabrication and storage conditions,
often overlooked due to their initially minor impact on device performance,
as these conditions critically affect material stability and charge
carrier dynamics.