First-principles calculations investigating structural, electronic optical and elastic properties of ABSe3 (A = Rb, Cs) compounds explored for photovoltaic and optoelectronics applications
Authors: Benbahouche Ly , Khelefhoum A , Boucetta S 
Published: November 2023

Abstract
In few recent years, great and significant efforts are devoted from researcher all over the world to pursue the revolution of photovoltaic’s materials and their uses in various applications. In the present work, a series of ab-initio simulations based on the density functional theory DFT plane wave pseudo-potential (PW-PP) method and hence performed towards the perselenoborate materials ABSe3 (A = Rb,Cs) for the first time along the three main polarizations of the incident wave directions [100], [010] and [001] with the aim of exploring their structural, electronic, optical and elastic properties. The generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE) carried out with CASTEP code is used for the exchange–correlation potential. The computed results showed that the structural properties of investigated compounds are very good agreement to the available experimental data, showing that the current calculations are quite accurate. Moreover, the density of states and electronic band structure calculations reveal that RbBSe3 (CsBSe3) compounds exhibit direct band gap semiconductor nature 1.66 eV (1,82 eV) respectively within the optimal range band gap 1eV–2eV required for photovoltaic’s applications makes them having great potential to obtain efficient Perovskite solar cell PSC. Additionally, our finding optical properties calculations reveal that the two investigated compounds exhibit strong absorption (prominent absorption peaks up 2,4 × 105cm−1) in UV range, while the real part of the refractive index for RbBSe3 (CsBSe3) was 2.62 (2.60) respectively which might be beneficial for photovoltaic application (top cell in solar cell) and optical applications. Also, high optical conductivity (∼1015sec−1) is found to be observed in visible ultraviolet range (1.7 eV to 30 eV). The lower reflectivity seen by RbBSe3 compared to CsBSe3 in the larger energy spectrum of electromagnetic radiation suggests that RbBSe3 compound is more suitable for electronic applications. Further, once the elastic constants are obtained, the calculated mechanical properties, bulk modulus (B), shear modulus (G), the ratio B/G, Young’s modulus (E), Poisson’s ratio (ν), anisotropy universal (AU) are calculated. Our calculated Young’s modulus indicate that the CsBSe3 is less hardness compared to RbBSe3, while Poisson’s ratio calculated leads them to have a character ionic and RbBSe3 is more ductile than CsBSe3. The calculation value of θ
D predicted from elastic constants appears low which is closely related to many physical properties such as specific heat and melting temperature. Finally, the finding results reveal another way of investigating mechanical stability, where both compounds are mechanically stable since all elastic constant computed are perfectly satisfied the Born stability criteria, flexible and brittle. Finally, we hope that all these results will be helpful for designing photovoltaic and optoelectronic devices.