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

Yi Teng Huang, Seán R. Kavanagh, Marcello Righetto, Marin Rusu, Igal Levine, Thomas Unold, Szymon J. Zelewski, Alexander J. Sneyd, Kaiwen Zhang, Linjie Dai, Andrew J. Britton, Junzhi Ye, Jaakko Julin, Mari Napari, Zhilong Zhang, James Xiao, Mikko Laitinen, Laura Torrente-Murciano, Samuel D. Stranks, Akshay RaoLaura M. Herz, David O. Scanlon, Aron Walsh, Robert L.Z. Hoye

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
Article number4960
JournalNature Communications
Volume13
Issue number1
DOIs
StatePublished - Dec 2022

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