Traps in the spotlight
How traps affect the charge carrier dynamics in Cs2AgBiBr6 perovskite
Valentina M. Caselli (TU Delft - ChemE/Opto-electronic Materials)
Jos Thieme (TU Delft - ChemE/O&O groep)
Huygen J. Jöbsis (Universiteit Utrecht)
S.A. Phadke (TU Delft - Large Scale Energy Storage)
Jiashang Zhao (TU Delft - ChemE/Opto-electronic Materials)
Eline M. Hutter (Universiteit Utrecht)
TJ Savenije (TU Delft - ChemE/Opto-electronic Materials)
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Abstract
Suitable optoelectronic properties of lead halide perovskites make these materials interesting semiconductors for many applications. Toxic lead can be substituted by combining monovalent and trivalent cations, such as in Cs2AgBiBr6. However, efficiencies of Cs2AgBiBr6-based photovoltaics are still modest. To elucidate the loss mechanisms, in this report, we investigate charge dynamics in Cs2AgBiBr6 films by double-pulse excitation time-resolved microwave conductivity (DPE-TRMC). By exciting the sample with two laser pulses with identical wavelengths, we found a clear photoconductance enhancement induced by the second pulse even 30 μs after the first laser pulse. Modeling the DPE-TRMC results, complemented by photoluminescence and transient absorption, we reveal the presence of deep emissive electron traps, while shallow hole trapping is responsible for the long-lived transient absorption signals. These long-lived carriers offer interesting possibilities for X-ray detectors or photocatalysis. The DPE-TRMC methodology offers unique insight into the times involved in charge trapping and depopulation in Cs2AgBiBr6.
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