Open AccessUltrafast Excited-State Localization in Cs2AgBiBr6 Double Perovskite
Author(s) -
Adam D. Wright,
Leonardo R. V. Buizza,
Kimberley J. Savill,
Giulia Longo,
Henry J. Snaith,
Michael B. Johnston,
Laura M. Herz
Publication year - 2021
Publication title -
the journal of physical chemistry letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.563
H-Index - 203
ISSN - 1948-7185
DOI - 10.1021/acs.jpclett.1c00653
Subject(s) - exciton , charge carrier , photoluminescence , materials science , delocalized electron , perovskite (structure) , photoconductivity , excited state , terahertz radiation , optoelectronics , band gap , ultrafast laser spectroscopy , ultrashort pulse , polaron , electron , condensed matter physics , spectroscopy , atomic physics , chemistry , optics , physics , crystallography , laser , organic chemistry , quantum mechanics
Cs 2 AgBiBr 6 is a promising metal halide double perovskite offering the possibility of efficient photovoltaic devices based on lead-free materials. Here, we report on the evolution of photoexcited charge carriers in Cs 2 AgBiBr 6 using a combination of temperature-dependent photoluminescence, absorption and optical pump-terahertz probe spectroscopy. We observe rapid decays in terahertz photoconductivity transients that reveal an ultrafast, barrier-free localization of free carriers on the time scale of 1.0 ps to an intrinsic small polaronic state. While the initially photogenerated delocalized charge carriers show bandlike transport, the self-trapped, small polaronic state exhibits temperature-activated mobilities, allowing the mobilities of both to still exceed 1 cm 2 V -1 s -1 at room temperature. Self-trapped charge carriers subsequently diffuse to color centers, causing broad emission that is strongly red-shifted from a direct band edge whose band gap and associated exciton binding energy shrink with increasing temperature in a correlated manner. Overall, our observations suggest that strong electron-phonon coupling in this material induces rapid charge-carrier localization.