Strong Fermi-level pinning at metal contacts to halide perovskites

Abstract

The performance of halide perovskite-based electronic and optoelectronic devices is often related to interfacial charge transport. To shed light on the underlying physical and chemical properties of CH3NH3PbI3 (MAPbI(3)) in direct contact with common electrodes Al, Ti, Cr, Ag, and Au, the evolution of interfacial properties and Fermi level pinning is systematically studied. Given a unique experimental facility, pristine interfaces without any exposure to ambient air were prepared. We observe aggregation of substantial amounts of metallic lead (Pb-0) at the metal/MAPbI(3) interface, resulting from the interfacial reaction between the deposited metal and iodine ions from MAPbI(3). It is found that the Schottky barrier height at the metal/MAPbI(3) interface is independent of the metal work function due to strong Fermi level pinning, possibly due to the metallic Pb-0 aggregates, which act as interfacial trap sites. The charge neutrality level of MAPbI(3) is consistent with the energy level of Pb-0-related defects, indicating that Pb-0 interfacial trap states can be nonradiative recombination sites. This work underlines that control of chemical bonding at interfaces is a key factor for designing future halide perovskite-based devices.