Bandgap Tunability and Charge Transport Properties of Mixed Antimony-Bismuth Cs2AgBi1-xSbxBr6 Halide Double Perovskites
Eline Hutter b, Maria Gelvez-Rueda a, Davide Bartesaghi a, Ferdinand Grozema a, Tom Savenije a
a Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
b Center for Nanophotonics, AMOLF, 1098 XG Amsterdam, The Netherlands
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Eline Hutter, presentation 093
DOI: https://doi.org/10.29363/nanoge.hopv.2019.093
Publication date: 11th February 2019

Halide double perovskites (HDPs) such as Cs2AgBiBr6 have recently emerged as non-toxic alternatives to lead-based perovskites, and were successfully applied as radiation absorbers both in sensitive X-ray detectors and in photovoltaic devices {1-2}. Still, the power conversion efficiencies of Cs2AgBiBr6-based solar cells are relatively low, which can be partially understood from its poor visible light absorption due to its indirect bandgap of 2.19 eV. It was recently shown that partially replacing the Bi3+ with Sb3+ can be used as a strategy to decrease the bandgap of Cs2AgBiBr6 toward values more relevant for single-junction solar cells {3}. However, although HDPs of various compositions have been designed, it remains unclear whether the transport properties of these HDPs are as favorable as for their lead-based analogues.

In this work, we study alloyed HDPs in which the Bi3+ is partially replaced with the non-toxic Sb3+, yielding HDP powders with the general formula Cs2AgBi1-xSbxBr6. The bandgaps of these materials are highly dependent on x and hence, tunable from 2.0 to 1.6 eV. We demonstrate that wet chemical processing of a solution containing Cs2AgBi1-xSbxBr6 powders in DMSO is a successful route to prepare thin films of these materials, which paves the way toward photovoltaic devices based on non-toxic HDPs with tunable bandgaps {4}. Additionally, using temperature-dependent time-resolved microwave conductivity techniques, we find that the mobility is proportional to T−p (with p ≈ 1.5). Importantly, this indicates that phonon scattering is the dominant scattering mechanism determining the charge carrier mobility in these HDPs, similar to the state-of-the-art lead-based perovskites. Altogether, these results pave the way toward photovoltaic devices based on non-toxic HDPs with tunable bandgaps.

Hemamala Karunadasa is acknowledged for facilitating this project and for critical feedback. The authors thank Adam Slavney for fruitful discussions. This work was supported by the Netherlands Organization for Scientific Research (NWO) under the Echo grant number: 712.014.007. E.M.H. received additional funding via a Fulbright Scholarship.

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