• Huang, Y.-T.; Kavanagh, S.R.; Righetto, M.; Rusu, M.; Levine, I.; Unold, T.; Zelewski, S.J.; Sneyd, A.J.; Zhang, K.; Dai, L.; Britton, A.J.; Ye, J.; Julin, J.; Napari, M.; Zhang, Z.; Xiao, J.; Laitinen, M.; Torrente-Murciano, L.; Stranks, S.D.; Rao, A.; Herz, L.M.; Scanlon, D.O.; Walsh, A.; Hoye, R.L.Z.: Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge carrier recombination. Nature Communications 13 (2022), p. 4960/1-13

Open Access Version

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 onemicrosecond 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. Thiswork reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics.