Tuning Electronic and Optical Properties of 2D/3D Interfaces of Hybrid Perovskites through Interfacial Charge Transfer: Prediction of Higher-Efficiency Interface Solar Cells Using Hybrid-DFT Methods.

The 2D/3D or 2D/quasi-2D composite mixed-dimensional construction of hybrid perovskite interfaces is gaining increasing attention due to their enhanced stability toward degradation without compromising the corresponding solar cell efficiency. Much of this is due to the interfacial charge transfer and its consequences on the electronic and optical response of the composite system, which are instrumental in the context of stability and efficiency. In this work, we have considered a case study of an experimentally motivated 2D/quasi-2D interface constructed based on Ruddlesden-Popper phases of (A43)PbI (2D phase) and (A43)MAPbI (quasi-2D phase) hybrid perovskites to envisage the unique tuning of electronic and optical properties through the associated charge transfer using density functional theory calculations based on both generalized gradient approximation as well as hybrid functionals, including corrections for nonlocal exchange obtained from Hartree-Fock. The corresponding tuning of the band gap is observed to be related to a unique charge transfer process between the 2D and quasi-2D counterparts of the interface mediated from the valence to conduction band edges of the composite. We have found that the optical absorption spectra can also be tuned by the construction of such a heterointerface and the emergence of a unique two-peak feature on the absorption edge, which is not present in either the 2D or quasi-2D hybrid perovskites. This feature is observed to be enhanced in the case of hybrid functionals, showing the importance of nonlocal exchange in optical spectra. We also compared the quasi-2D structure with the prototypical 3D structure MAPbI to show the progression of properties with dimensionality. The formation of the composite interface is found to increase the spectroscopic limited maximum efficiency for the use of these materials as solar cells from ≈24% for individual components to ≈32% for the composite heterostructure.