Researchers Sanchi Monga and Saswata Bhattacharya from the University of California, Santa Cruz, have published a study in the journal Physical Review Materials that explores the potential of a new class of materials for photovoltaic applications. The materials in question are antiperovskite carbides, specifically M$_6$CSe$_4$ where M can be either calcium (Ca) or strontium (Sr).
The study employs advanced computational techniques, including density functional theory (DFT) and many-body perturbation theory (GW), to investigate the electronic, optical, and excitonic properties of these materials. The researchers found that both Ca$_6$CSe$_4$ and Sr$_6$CSe$_4$ are direct band gap semiconductors, meaning they have a direct transition between the valence band and the conduction band, which is a desirable property for photovoltaic materials. The band gaps of these materials span the infrared-visible region, making them potentially useful for harvesting solar energy.
The researchers also examined the optical properties of these materials, finding that they exhibit bound excitons, which are pairs of electrons and holes bound together by electrostatic forces. The binding energies of these excitons were found to be 0.12 eV for Ca$_6$CSe$_4$ and 0.20 eV for Sr$_6$CSe$_4$. These excitons extend over nearly three unit cells in all directions, indicating that they are relatively large and stable.
The study also looked at the non-radiative recombination dynamics of these materials, which is the process by which excited electrons and holes lose energy without emitting light. The researchers found that Ca$_6$CSe$_4$ exhibits pronounced lattice fluctuations, resulting in larger band gap variations and faster electronic decoherence. However, these effects also lead to non-radiative recombination lifetimes that are approximately eleven times longer than in Sr$_6$CSe$_4$. This means that Ca$_6$CSe$_4$ has a greater potential for converting solar energy into electrical energy efficiently.
Overall, the study identifies M$_6$CSe$_4$ carbides as promising lead-free photovoltaic materials, with Ca$_6$CSe$_4$ exhibiting superior optoelectronic properties and carrier dynamics. The researchers suggest that these findings motivate further experimental investigation into these materials for use in solar cells and other optoelectronic devices. The research was published in the journal Physical Review Materials.
This article is based on research available at arXiv.