Publication date: 15th December 2025
Bismuth halide semiconductors are promising lead-free alternatives to halide perovskites for (indoor) photovoltaics and photocatalysis, but their optoelectronic performance is limited by wide, indirect bandgaps and large exciton binding energies that hinder charge separation. Compositional alloying provides an effective strategy to overcome these limitations by enabling controlled tuning of optical and excitonic properties.
We found that solvent-free mechanochemical synthesis results in enormous control over alloying ratio, and we have successfully prepared a wide variety of compositions with bandgaps spanning the entire visible of the spectrum, e.g. Cs2AgBi1-yMyBr6 and Cs3Bi2(BryIy)9. XRD and Raman analysis on Cs3Bi2(Br1−xIx)9 powders confirms the atomic-level halide mixing and compositional control across the series. In addition, we find that the excitonic properties can be steered by the type of halide, reaching a minimum at x = 0.6. Interestingly, this minimum exciton binding energy coincides with the lowest band-gap value, the smallest Urbach energy and the longest lifetimes, collectively indicating the mixing range (around x = 0.6) with the most favorable optoelectronic characteristics.
In parallel, we address the formation mechanisms of alloyed bismuth-based halide elpasolites synthesized by mechanochemical ball milling. In situ synchrotron X-ray diffraction of Cs2AgBi1-yMyBr6 (M = Sb3+, In3+, Fe3+) reveals distinct crystallization pathways depending on the substituent cation. We identify the reaction intermediates for the parent composition Cs2AgBiBr6, and find that –Bi0.5Sb0.5– forms via a similar reaction pathway. Alloying with In3+ or Fe3+ on the other hand occurs via an additional cation-exchange step. These insights into the mechanochemical formation mechanisms of alloyed bismuth halides provide guidelines towards rational compositional engineering of complex materials, with controlled optical and excitonic properties.
References:
Jöbsis H.J., Fykouras K., Reinders J.W.C., van Katwijk J., Dorresteijn J.M., Arens T., Vollmer I., Muscarella L.A., Leppert L., Hutter E.M.
Conduction Band Tuning by Controlled Alloying of Fe into Cs2AgBiBr6 Double Perovskite Powders
Advanced Functional Materials, 2024, 34 (50), art. no. 2306106
Biega R.-I., Jöbsis H.J., Gijsberg Z., Huskens M., Hutter E.M., Leppert L.
Halide Mixing in Cs2AgBi(IxBr1-x)6 Double Perovskites: A Pathway to Tunable Excitonic Properties
Journal of Physical Chemistry C, 2024,128 (35), pp. 14767 – 14775.
Jöbsis H.J., Muscarella L.A., Andrzejewski M., Casati N.P.M., Hutter E.M.
Mechanochemical Formation Mechanism of Alloyed AgBi-elpasolites
Journal of the American Chemical Society, 2025, 147, 24519 – 24526.
nanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.
Previously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.
International Conference on Hybrid and Organic Photovoltaics
International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
The main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.
The International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.