Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge-carrier recombination.

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I-V-VI2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly-rising absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >105 cm-1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics.


Funder: AiF Project, no: ZIM-KK5085302DF0

Funder: Polish National Agency for Academic Exchange within the Bekker programme (grant no. PPN/BEK/2020/1/00264/U/00001)

Funder: Royal Society Te Apārangi and the Cambridge Commonwealth European and International Trust

Funder: Hans Fischer Senior Fellowship from the Technical University of Munich's Institute for Advanced Study, funded by the German Excellence Initiative

Article, /639/301/299/946, /639/638/298/917, /119/118, /128, /147/3, /147/28, /147/143, /140/125, /140/146, /145, article
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Nat Commun
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Springer Science and Business Media LLC
Engineering and Physical Sciences Research Council (EP/L016087/1)
European Research Council (756962)
Engineering and Physical Sciences Research Council (EP/R023980/1)
Engineering and Physical Sciences Research Council (EP/S030638/1)
Engineering and Physical Sciences Research Council (EP/R00661X/1)