Multiscale simulations of thermal and non-thermal responses of photovoltaic materials to ultrafast X-ray irradiation

Abstract Lead sulfide (PbS), cadmium telluride (CdTe), and indium tin oxide (ITO) play crucial roles in various electronic applications where laser treatment enables precise modification of their distinctive electronic characteristics. This study utilizes the XTANT-3 hybrid/multiscale model to investigate the microscopic response of these materials to ultrafast X-ray irradiation. The model simultaneously traces intertwined processes of non-equilibrium dynamics of both electrons and atoms, electron-phonon coupling, and nonthermal melting via changes in the interatomic potential induced by the excitation of electrons. Among the materials studied, CdTe exhibits the highest radiation resistance, similar to cadmium sulfide (CdS). At the respective threshold doses, the melting is primarily thermal, driven by electron-phonon coupling, which is accompanied by the band gap closure. Additionally, all materials exhibit nonthermal melting at higher doses. Energy dissipation pathways and material recrystallization increases the damage thresholds substantially. In CdTe and PbS, below 1.5 eV/atom, the band gap returns to its original value upon recrystallization. As the dose increases, the resulting cooled material becomes increasingly amorphous, progressively reducing the band gap until a stable configuration is reached. Notably, in a narrow window of deposited doses, ITO exhibits transient superionic behavior, with the liquid oxygen but solid indium (In) and tin (Sn) sublattices. At 0.6 eV/atom in CdTe and 0.4 eV/atom in PbS and ITO, material ablation from the surface occurs at the ten-picosecond timescale.