The development of solar photovoltaic electricity generation requires the development of new materials for converting solar radiation into electron-hole pairs. Organic-inorganic hybrid perovskites (HOIPs) of the CsPbI3 type, with substitutions of Cs by formamidinium (FA) and/or methylammonium (MA) ions, have emerged as very promising materials in terms of performance and manufacturing.

Substitutions of Cs with elements such as Rb, Pb with Sn, and I with Br are also being considered to improve stability or performance. The synthesis and optimization of the composition of layers of such materials require a better understanding of their thermodynamic equilibrium properties and stability.

The objective is to construct a thermodynamic model of the Cs-Rb-FA-Pb-Sn-I-Br system. The approach uses the CALPHAD method, which focuses on building a database and an analytical formulation of thermodynamic potential capable of reproducing thermodynamic and phase diagram data. A critical review of the data in the literature will enable this database to be initialized and the data to be evaluated. In order to feed the model with thermodynamic data on enthalpy of formation and heat capacity, electronic structure calculations using DFT (Density Functional Theory) post-processed by the quasi-harmonic approximation of quantum solid theory will be performed to calculate these properties and also provide structural data on these materials. If necessary, measurements may also be carried out using heat treatments, Differential Thermal Analysis and calorimetry. Calculations will be performed using the database in order to optimize manufacturing processes and identify the most promising compositions.

The host laboratory (LM2T) based at ISAS (Institute for Analytical Sciences and Simulation for Low-Carbon Energy) at CEA-Saclay has extensive experience in this type of activity and has both experimental and computational resources at its disposal. For this project, it is working in collaboration with the CEA units based in Grenoble and Chambéry (DTS and DTNM), which develop solar cells.