Molecular passivation of MAPbI3 perovskite films follows the Langmuir adsorption rule

Surface defect passivation through additional molecular bonding plays a crucial role in optimization of perovskite-based photovoltaic devices. So far, quantization of the defect site coverage by molecular passivation remains unclear from a macroscopic view. We herein unravel the coverage possibility of the surface defect sites of perovskite films by the added molecule passivators upon an MAPbI3 perovskite system. Concerns of inconsistent time-resolved photoluminescence (TRPL) spectroscopic measurements are dispelled by vapor-deposition fabrications of highly uniform perovskite films. The surface defect densities of perovskite films are derived from global fittings of the charge carrier dynamics to the measured TRPL decays. It is revealed the Langmuir adsorption relationship of the defect site coverage with respect to the added amount of tri-n-octylphosphine oxide passivation molecules. Our work supplements the dynamical bonding model of the molecular passivation process and provides reliable knowledge upon the bonding process between molecules and defects, which leads to rationalized surface passivation methodologies in perovskite photovoltaics communities.