Charge-carrier mobility and localization in semiconducting CU2AGBiI6 for photovoltaic applications

Journal article

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 Cu2AgBiI6 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 Cu2AgBiI6 are subject to strong charge-lattice coupling. However, such small polarons still exhibit mobilities in excess of 1 cm2 V–1 s–1 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 Cu2AgBiI6 as an attractive lead-free material for photovoltaic applications.

Authors: Buizza, LRV; Wright, AD; Longo, G; Sansom, HC; Xia, CQ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: ACS Energy Letters
• Volume: 6
• Issue: 5
• Pages: 1729-1739
• Place of publication: United States
• Publication date: 2021-04-07
• Acceptance date: 2021-03-31
• DOI: 10.1021/acsenergylett.1c00458
• EISSN: 2380-8195
• ISSN: 2380-8195
• Pmid: 34056108
• Language: English
• Keywords: FFR