Two-dimensional CsPbI/CsPbBr vertical heterostructure: a potential photovoltaic absorber.

First-principles methods have been employed here to calculate structural, electronic and optical properties of CsPbI and CsPbBr, in monolayer and heterostructure (HS) (PbI-CsBr (HS1), CsI-CsBr (HS2), CsI-PbBr (HS3) and PbI-PbBr (HS4)) configurations. Imaginary frequencies are absent in phonon dispersion curves of CsPbI and CsPbBr monolayers which depicts their dynamical stability. Values of interfacial binding energies signifies stability of our simulated heterostructures. The CsPbI monolayer, CsPbBr monolayer, HS1, HS2, HS3 and HS4 possess direct bandgap of 2.19 eV, 2.73 eV, 2.41 eV, 2.11 eV, 1.88 eV and 2.07 eV, respectively. In the HS3, interface interactions between its constituent monolayers causes substantial decrease in its resultant bandgap which suggests its solar cell applications. Static dielectric constants of all simulated heterostructures are higher when compared to those of pristine monolayers which demonstrates that these heterostructures possess low charge carrier recombination rate. In optical absorption plots of materials, the plot of HS3 displayed a red shift and depicted absorption of a substantial part of visible spectrum. Later on, via Shockley-Queisser limit we have calculated solar cell parameters of all the reported structures. The calculations showed that HS2, HS3 and HS4 showcased enhanced power conversion efficiency compared to CsPbI and CsPbBr monolayers when utilized as an absorber layer in solar cells.