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We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q = S, Se) monolayers. The dynamic stability of 2Dwrinkle like-PdQ2 is proven by positive phonon frequencies in the phonon dispersion curve. The optimized structural parameters of wrinkled pentagonal PdQ2 are in good agreement with the available experimental results. The ultimate tensile strength (UTHS) was calculated and found that, penta-PdS2 monolayer can withstand up to 16% (18%) strain along x (y) direction with 3.44 GPa (3.43 GPa). While, penta-PdSe2 monolayer can withstand up to 17% (19%) strain along x (y) dirrection with 3.46 GPa (3.40 GPa). It is found that, the penta-PdQ2 monolayers has the semiconducting behavior with indirect band gap of 0.94 and 1.26 eV for 2D-PdS2 and 2D-PdSe2, respectively. More interestingly, at room temperacture, the hole mobilty (electron mobility) obtained for 2D-PdS2 and PdSe2 are 67.43 (258.06) cm2 V−1 s−1 and 1518.81 (442.49) cm2 V−1 s−1, respectively. In addition, I-V characteristics of PdSe2 monolayer show strong negative differential conductance (NDC) region near the 3.57 V. The Shockly-Queisser (SQ) effeciency prameters of PdQ2 monolayers are also explored and the highest SQ efficeinciy obtained for PdS2 is 33.93% at −5% strain and for PdSe2 is 33.94% at −2% strain. The penta-PdQ2 exhibits high optical absorption intensity in the UV region, up to 4.04 × 105 (for PdS2) and 5.28 × 105 (for PdSe2), which is suitable for applications in optoelectronic devices. Thus, the ultrathin PdQ2 monolayers could be potential material for next-generation solar-cell applications and high performance nanodevices.

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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.