First-Principles Study of Mn-Doped and Nb-Doped CsPbCl₃ Monolayers as an Absorber Layer in Solar Cells

The density functional theory (DFT) based analysis of cubic phase cesium lead chloride (CsPbCl₃) perovskite is reported. Here the absence of imaginary frequencies in the phonon dispersion curves of unit cell of bulk and monolayer CsPbCl₃ showed that both the structures are dynamically stable. The pristine CsPbCl₃ monolayer is a wide bandgap semiconductor with an energy gap of 3.24 eV; therefore, an approach to alter its properties was adopted by doping Mn at the Pb-site and Nb at the Cs-site, respectively. In these Mn- and Nb-doped CsPbCl₃ monolayers, intermediate states were generated in both the cases due to Mn-3d and Nb-4d orbitals, respectively, which makes the transfer of excited photoelectrons easier from the valence band to the conduction band. The absorption coefficient plots of Mn-doped and Nb-doped CsPbCl₃ monolayers indicated that their absorption edges get shifted toward low photon energy, i.e. red shifted compared to the pristine CsPbCl₃ monolayer. As both the impurity atoms considered are transition metals, we have also taken into account the effect of spin polarization on electronic and optical properties of doped monolayers. Solar cell parameters of all of these monolayers have been calculated using the Shockley-Queisser (SQ) limit. The short-circuit current density (J_sc) of the Nb-doped CsPbCl₃ monolayer was obtained around 655.45 A/m², and the efficiency of this material came out to be around 15.68%. For the Mn-doped CsPbCl₃ monolayer the value of J_sc came to be around 525.68 A/m² and showed strikingly high efficiency of 26.88% thus being a suitable candidate for its application as an absorber layer in solar cells.