Lead free perovskites, especially Bi-based perovskites, are excellent candidates for replacing Pb-based perovskite absorbers in the large scale commercialization of perovskite solar cells due to the high toxicity of Pb. However, before their practical application, it is of importance to understand the fate of their photoexcited charger carriers for helping optimize their solar cells performance. By employing ultrafast laser initialized time-resolved X-ray absorption spectroscopy, we have successfully characterized the representative lead free Bi-based perovskite (Cs3Bi2Br9) nanocrystals with a mean size of ~ 4 nm. Probing at Bi L3 edge indicates that the electrons are freely delocalized in the conduction band. However, the results probed at Br K edge identify that the photogenerated holes are strongly localized at Br atoms, forming strong exciton-polarons alive for tens of ns. Our time-resolved element-specific study of lead-free perovskites will advance the understanding of the mobility of photogenerated carriers in solar cell materials.

Fate of photoexcited charge carriers in lead-free perovskite nanocrystals for excitonic solar cells

254th National Meeting (2017)

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