Highly Absorbing Lead-Free Semiconductor Cu<sub>2</sub>AgBiI<sub>6</sub> for Photovoltaic Applications from the Quaternary CuI-AgI-BiI<sub>3</sub> Phase Space.



Sansom, Harry C, Longo, Giulia, Wright, Adam D, Buizza, Leonardo RV, Mahesh, Suhas, Wenger, Bernard, Zanella, Marco ORCID: 0000-0002-6164-6169, Abdi-Jalebi, Mojtaba, Pitcher, Michael J, Dyer, Matthew S ORCID: 0000-0002-4923-3003
et al (show 6 more authors) (2021) Highly Absorbing Lead-Free Semiconductor Cu<sub>2</sub>AgBiI<sub>6</sub> for Photovoltaic Applications from the Quaternary CuI-AgI-BiI<sub>3</sub> Phase Space. Journal of the American Chemical Society, 143 (10). 3983 - 3992.

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Abstract

Since the emergence of lead halide perovskites for photovoltaic research, there has been mounting effort in the search for alternative compounds with improved or complementary physical, chemical, or optoelectronic properties. Here, we report the discovery of Cu<sub>2</sub>AgBiI<sub>6</sub>: a stable, inorganic, lead-free wide-band-gap semiconductor, well suited for use in lead-free tandem photovoltaics. We measure a very high absorption coefficient of 1.0 × 10<sup>5</sup> cm<sup>-1</sup> near the absorption onset, several times that of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>. Solution-processed Cu<sub>2</sub>AgBiI<sub>6</sub> thin films show a direct band gap of 2.06(1) eV, an exciton binding energy of 25 meV, a substantial charge-carrier mobility (1.7 cm<sup>2</sup> V<sup>-1</sup> s<sup>-1</sup>), a long photoluminescence lifetime (33 ns), and a relatively small Stokes shift between absorption and emission. Crucially, we solve the structure of the first quaternary compound in the phase space among CuI, AgI and BiI<sub>3</sub>. The structure includes both tetrahedral and octahedral species which are open to compositional tuning and chemical substitution to further enhance properties. Since the proposed double-perovskite Cs<sub>2</sub>AgBiI<sub>6</sub> thin films have not been synthesized to date, Cu<sub>2</sub>AgBiI<sub>6</sub> is a valuable example of a stable Ag<sup>+</sup>/Bi<sup>3+</sup> octahedral motif in a close-packed iodide sublattice that is accessed via the enhanced chemical diversity of the quaternary phase space.

Item Type: Article
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 25 Mar 2021 11:16
Last Modified: 29 Nov 2021 19:10
DOI: 10.1021/jacs.1c00495
Open Access URL: https://doi.org/10.1021/jacs.1c00495
URI: https://livrepository.liverpool.ac.uk/id/eprint/3118153