posted on 2020-06-09, 18:34authored byGiulia Longo, Suhas Mahesh, Leonardo R. V. Buizza, Adam D. Wright, Alexandra J. Ramadan, Mojtaba Abdi-Jalebi, Pabitra K. Nayak, Laura M. Herz, Henry J. Snaith
Double
perovskites have recently emerged as possible alternatives
to lead-based halide perovskites for photovoltaic applications. In
particular, Cs2AgBiBr6 has been the subject
of several studies because of its environmental stability, low toxicity,
and its promising optoelectronic features. Despite these encouraging
features, the performances of solar cells based on this double perovskite
are still low, suggesting severe limitations that need to be addressed.
In this work we combine experimental and theoretical studies to show
that the short electron diffusion length is one of the major causes
for the limited performance of Cs2AgBiBr6 solar
cells. Using EQE measurements on semitransparent Cs2AgBiBr6 solar cells we estimate the electron diffusion length to
be only 30 nm and corroborated this value by terahertz spectroscopy.
By using photothermal deflection spectroscopy and surface photovoltage
measurements we correlate the limited electron diffusion length with
a high density of electron traps. Our findings highlight important
faults affecting this double perovskite, showing the challenges to
overcome and hinting to a possible path to improve the efficiency
of Cs2AgBiBr6 solar cells.