Structural and electronic features of Si/CH3NH3PbI3 interfaces with optoelectronic applicability: Insights from first-principles

Abstract

Motivated by the complete lack of theoretical knowledge in view of their applications in solar device processing and in optoelectronics, I have here investigated the structural and the electronic properties of interfaces constituted by the most relevant technological surface of silicon, i.e. the (001), and methylammonium (MA) lead iodide (001)-oriented surfaces. Results show a thermodynamic enhanced stability in the case of the lead iodide (PbI2-) terminated CH3NH3PbI3/Si interface, while the other investigated termination, the MAI-rich one, shows a better alignment between bandedges once interfaced with Si. Indeed, while for the latter a clear type-II heterojunction is observed, the former still shows a type-II behavior where anyway conduction band minima of Si and CH3NH3PbI3 are (almost) degenerate. The DOS show the raise of p-like states in the gap close to the valence band due to the strain present at the Si-Si and at the equatorial Pb-I bonds in the PbI2-terminated/Si interface and indicate the unsuitability of this interface for optoelectronic applications. The present work reveals how the chemistry of the interface, i.e. the different bonding arrangement between silicon and CH3NH3PbI3, induces completely different carrier transport properties along the heterostructure with potentially detrimental effects in the final device. To date, this work is the first theoretical modellization of the interface between these two semiconductors and provides important information in the processes involved in 2-terminal tandem device assembling and in all the processes of perovskite growth on silicon substrate.