Silver-Bismuth based 2D Double Perovskites (4FPEA)4AgBiX8 (X=Cl, Br, I): Highly Oriented Thin Films with Large Domain Sizes and Ultrafast Charge-Carrier Localization
Rik Hooijer a, Andreas Weis a, Alexander Biewald a, Maximilian T. Sirtl a, Julian Malburg a, Rico Holfeuer a, Simon Thamm a, Amir Abbas Yousefi Amin a, Marcello Righetto b, Achim Hartschuh a, Laura M. Herz b, Thomas Bein a
a University of Munich (LMU), Department of Chemistry and Center for Nanoscience (CeNS), 81377 Múnich, Alemania, Múnich, Germany
b Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, U.K.
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Rik Hooijer, presentation 087
Publication date: 20th April 2022

Two-dimensional (2D) hybrid double perovskites are a promising emerging class of materials featuring superior intrinsic and extrinsic stability over their three-dimensional (3D) parent structures, while enabling additional structural diversity and tunability.[1] Here, we expand the Ag-Bi based double perovskite system, comparing structures obtained with the halides chloride, bromide and iodide and the organic spacer cation 4-fluorophenethylammonium (4FPEA) to form the n = 1 Ruddlesden-Popper (RP) phases (4FPEA)4AgBiX8 (X = Cl, Br, I). We demonstrate access to the iodide RP-phase through a simple organic spacer, analyze the different properties as a result of halide substitution and incorporate the materials into photodetectors. Highly oriented thin films with very large domain sizes are fabricated and investigated with grazing incidence wide angle X-ray scattering, revealing a strong dependence of morphology on substrate choice and synthesis parameters. First-principles calculations confirm a direct band gap and show type Ib and IIb band alignment between organic and inorganic quantum wells. Optical characterization, temperature-dependent photoluminescence and optical-pump terahertz-probe spectroscopy give insights into the absorption and emissive behavior of the materials as well as their charge-carrier dynamics. Overall, we further elucidate the possible reasons for the electronic and emissive properties of these intriguing materials, dominated by phonon-coupled and defect-mediated polaronic states.

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