Christos Tyrpenou PhD defense

Abstract
This thesis investigates lead-free halide materials using first-principles computational methods, with particular emphasis on the relationships between crystal structure, stability, and optoelectronic properties. Hypothetical Ag–In ternary compounds are examined to determine how chemical substitution affects their structural, electronic, and optical behavior. The analysis is further extended to broader compositional and configurational phase spaces, enabling the identification of general stability trends and preferred local configurations across Bi-, Sb-, and In-based halide compounds containing Cu or Ag. Layered halide double perovskites are also investigated, with particular attention to phase stability and the influence of pressure on photoluminescence. The calculations are used to distinguish between competing structural models and to elucidate the microscopic origins of experimentally observed optical responses. Overall, this work demonstrates how computational modelling can complement synthesis and characterization, facilitate the prediction and identification of stable compounds, and provide fundamental insight into the properties of complex lead-free halide materials.

Jury
Claudine katan, CNRS Research Director, iscr, University of Rennes / President
Monica morales-masis, Profesor, Eindhoven University of Technology / Examiner
Thomas stergiopoulos, Senior Researcher, Institute of Nanoscience and Nanotechnology, ncsr Demokritos / Examiner
Emilie gaudry, Professor, Mines nancy, University of Lorraine / Reviewer
Claudio quarti, fnrs Researcher, CMN, University of Mons / Reviewer

Supervisors
George volonakis, Professor, iscr, University of Rennes / PhD Director
Mikaël kepenekian, CNRS Research Director, iscr, University of Rennes / PhD Co-Director

Contacts
[Yorgos Volonakis](https://iscr.univ-rennes.fr/george-volonakis), [yorgos.volonakis@univ-rennes.fr](mailto:yorgos.volonakis@univ-rennes.fr)
[Mikaël kepenekian](https://iscr.univ-rennes.fr/mikael-kepenekian), [mikael.kepenekian@univ-rennes.fr](mailto:mikael.kepenekian@univ-rennes.fr)
[Christos Tyrpenou](https://iscr.univ-rennes.fr/christos-tyrpenou), [christos.tyrpenou@univ-rennes.fr](mailto:christos.tyrpenou@univ-rennes.fr)