Charge-Carrier Mobility and Localization in Semiconducting Cu<sub>2</sub>AgBiI<sub>6</sub> for Photovoltaic Applications

Buizza, Leonardo RV, Wright, Adam D, Longo, Giulia, Sansom, Harry C, Xia, Chelsea Q, Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483, Johnston, Michael B, Snaith, Henry J and Herz, Laura M
(2021) Charge-Carrier Mobility and Localization in Semiconducting Cu<sub>2</sub>AgBiI<sub>6</sub> for Photovoltaic Applications. ACS ENERGY LETTERS, 6 (5). pp. 1729-1739.

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Lead-free silver-bismuth semiconductors have become increasingly popular materials for optoelectronic applications, building upon the success of lead halide perovskites. In these materials, charge-lattice couplings fundamentally determine charge transport, critically affecting device performance. In this study, we investigate the optoelectronic properties of the recently discovered lead-free semiconductor Cu<sub>2</sub>AgBiI<sub>6</sub> using temperature-dependent photoluminescence, absorption, and optical-pump terahertz-probe spectroscopy. We report ultrafast charge-carrier localization effects, evident from sharp THz photoconductivity decays occurring within a few picoseconds after excitation and a rise in intensity with decreasing temperature of long-lived, highly Stokes-shifted photoluminescence. We conclude that charge carriers in Cu<sub>2</sub>AgBiI<sub>6</sub> are subject to strong charge-lattice coupling. However, such small polarons still exhibit mobilities in excess of 1 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup> at room temperature because of low energetic barriers to formation and transport. Together with a low exciton binding energy of ∼29 meV and a direct band gap near 2.1 eV, these findings highlight Cu<sub>2</sub>AgBiI<sub>6</sub> as an attractive lead-free material for photovoltaic applications.

Item Type: Article
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 09 Aug 2021 08:33
Last Modified: 18 Oct 2023 08:37
DOI: 10.1021/acsenergylett.1c00458
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