Proceedings of nanoGe Fall Meeting 2021 (NFM21)
DOI: https://doi.org/10.29363/nanoge.nfm.2021.213
Publication date: 23rd September 2021
Cs2AgBiBr6 (CABB) has been proposed as a less toxic and more stable alternative to lead halide perovskites, and was successfully implemented as photoactive layer in optoelectronic devices. However, power conversion efficiencies of CABB-based devices remain much lower than compared to their lead-based analogues, suggesting poor charge transport. On the other hand, microsecond lifetimes have been reported for CABB. In this talk, I will elaborate on the dynamics of charge transport, localization and recombination in CABB thin films, studied using time-resolved photoconductivity and transient absorption/reflectance measurements. On comparing the temperature-dependent photoconductivity measurements of CABB with lead-based perovskites, we find a similar band-like charge transport mechanism.1 We also find that replacing Bi with Sb shifts the absorption onset, while preserving the charge transport mechanism. In contrast to state-of-the-art lead-based perovskites however, charges in CABB lose mobility within tens of nanoseconds, so that diffusion lengths remain relatively short (~100 nm). Using microsecond transient absorption measurements, we observe that these non-mobile charges have a lifetime of several microseconds, suggesting a long-lived localized state. In contrast with the nanosecond-lifetime observed for mobile charges, we observe microsecond-long lifetimes in transient absorption measurements. The observation that the diffusion length is similar to the grain size suggests that charge localization occurs at the surfaces. Therefore, improving surface quality could be a strategy to optimize performance of CABB-based optoelectronic devices.
Finally, we performed a toxicity study of methylammonium lead iodide perovskites on A. Thaliana plants, and found that the iodide was actually much more toxic than the lead. Altogether, these results stress the importance of further understanding which perovskites are most harmful to the environment, while optimizing the optoelectronic quality of materials with the lowest toxicity.
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