Highly Absorbing Lead-Free Semiconductor Cu2AgBiI6for Photovoltaic Applications from the Quaternary CuI-AgI-BiI3Phase Space

Harry C. Sansom, Giulia Longo, Adam D. Wright, Leonardo R.V. Buizza, Suhas Mahesh, Bernard Wenger, Marco Zanella, Mojtaba Abdi-Jalebi, Michael J. Pitcher, Matthew S. Dyer, Troy D. Manning, Richard H. Friend, Laura M. Herz, Henry J. Snaith, John B. Claridge, Matthew J. Rosseinsky*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)
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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 Cu2AgBiI6: 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 × 105 cm-1 near the absorption onset, several times that of CH3NH3PbI3. Solution-processed Cu2AgBiI6 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 cm2 V-1 s-1), 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 BiI3. 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 Cs2AgBiI6 thin films have not been synthesized to date, Cu2AgBiI6 is a valuable example of a stable Ag+/Bi3+ octahedral motif in a close-packed iodide sublattice that is accessed via the enhanced chemical diversity of the quaternary phase space.

Original languageEnglish
Pages (from-to)3983-3992
Number of pages10
JournalJournal of the American Chemical Society
Issue number10
Early online date8 Mar 2021
Publication statusPublished - 17 Mar 2021
Externally publishedYes


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