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

• Published in: Nature communications Vol. 13; no. 1; p. 4960
• Main Authors: Huang, Yi-Teng, Kavanagh, Seán R., Righetto, Marcello, Rusu, Marin, Levine, Igal, Unold, Thomas, Zelewski, Szymon J., Sneyd, Alexander J., Zhang, Kaiwen, Dai, Linjie, Britton, Andrew J., Ye, Junzhi, Julin, Jaakko, Napari, Mari, Zhang, Zhilong, Xiao, James, Laitinen, Mikko, Torrente-Murciano, Laura, Stranks, Samuel D., Rao, Akshay, Herz, Laura M., Scanlon, David O., Walsh, Aron, Hoye, Robert L. Z.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 24.08.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 140/125; 140/146; 147/143; 147/28; 147/3; 639/301/299/946; 639/638/298/917; Absorption; Absorptivity; Carrier recombination; Carrier transport; Cations; Chalcogenides; Crystals; Current carriers; Decay; Decay rate; Electron states; Electronics industry; Humanities and Social Sciences; Kinetics; Localization; multidisciplinary; Nanocrystals; Photoconductivity; Photovoltaics; Recombination; Science; Science (multidisciplinary); Solar energy absorbers; Valence band
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-022-32669-3

I-V-VI 2 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 NaBiS 2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >10 5  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 NaBiS 2 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. Ternary chalcogenides are gaining interest as nontoxic, stable solar absorbers. Here, the authors investigate NaBiS 2 , finding cation disorder to be a critical parameter that enables its high absorption strength and unusual charge-carrier kinetics.