TY - JOUR
T1 - Excitons and narrow bands determine the optical properties of cesium bismuth halides
AU - Rieger, Sebastian
AU - Bohn, Bernhard J.
AU - Döblinger, Markus
AU - Richter, Alexander F.
AU - Tong, Yu
AU - Wang, Kun
AU - Müller-Buschbaum, Peter
AU - Polavarapu, Lakshminarayana
AU - Leppert, Linn
AU - Stolarczyk, Jacek K.
AU - Feldmann, Jochen
N1 - Funding Information:
This work was supported by the Bavarian State Ministry of Science, Research, and Arts through the grant “Solar Technologies go Hybrid (SolTech),” by the China Scholarship Council (Y.T. and K.W.) and by the Deutsche Forschungsgemeinschaft (DFG) through the excellence cluster “e-conversion.” L.L. acknowledges financial support by the Elite Network Bavaria and computational resources provided by the Bavarian Polymer Institute and DFG via SFB840. Portions of this work were also supported by National Energy Research Scientific Computing Center (NERSC), a US Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231.
Publisher Copyright:
© 2019 American Physical Society.
PY - 2019/11/20
Y1 - 2019/11/20
N2 - We study the optical properties of Cs3Bi2I9 nanoplatelets using a combination of first-principles density functional theory, GW plus Bethe-Salpeter equation calculations, and spectroscopic experiments. We show that the material exhibits flat bands and hence high effective masses. This manifests itself in the lowest-energy transition in the absorption spectrum arising from excitons with a high binding energy of 300 meV and a Bohr radius smaller than 6 nm. Due to the indirect band gap, electrons and holes are efficiently separated in reciprocal space and recombine slowly across the band gap, leading to very weak photoluminescence. Our results resolve inconsistencies in previous studies on Cs3Bi2I9 and lay the groundwork for further applications of this material, reliant on charge separation.
AB - We study the optical properties of Cs3Bi2I9 nanoplatelets using a combination of first-principles density functional theory, GW plus Bethe-Salpeter equation calculations, and spectroscopic experiments. We show that the material exhibits flat bands and hence high effective masses. This manifests itself in the lowest-energy transition in the absorption spectrum arising from excitons with a high binding energy of 300 meV and a Bohr radius smaller than 6 nm. Due to the indirect band gap, electrons and holes are efficiently separated in reciprocal space and recombine slowly across the band gap, leading to very weak photoluminescence. Our results resolve inconsistencies in previous studies on Cs3Bi2I9 and lay the groundwork for further applications of this material, reliant on charge separation.
UR - http://www.scopus.com/inward/record.url?scp=85108261734&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.100.201404
DO - 10.1103/PhysRevB.100.201404
M3 - Article
VL - 100
JO - Physical review B: Covering condensed matter and materials physics
JF - Physical review B: Covering condensed matter and materials physics
SN - 2469-9950
IS - 20
M1 - 201404
ER -