Optimization of fluorinated interfacial layers with minimal surface coverage for hybrid perovskite materials

Abstract

Minimal surface coverage using fluorinated interfacial adlayers is optimized in view of passivating non-radiative recombination sites and tuning the electronic properties of hybrid perovskite materials. A combination of XPS, Kelvin probe, and contact angle measurements allows characterization of the material surface's composition, surface potential and wettability. Polarization modulation infrared reflection absorption spectroscopy reveals that for the tetra(fluoroalkyl)stannanes and chlorotri(fluoroalkyl)stannanes studied, the wettability and work function of the modified surface result from the organization of the adlayer's molecular components and propensity to selectively passivate defects. Our results show that the surface potential of methylammonium lead triiodide can be tuned over a 230 mV range using a mono-molecular adlayer of chlorotri(fluoroalkyl)stannane whereas the tetra(fluoroalkyl)stannanes provide the strongest hydrophobicity (contact angle >80°) with little change in the surface potential. Photoluminescence quantum efficiency (PLQE) and time-resolved luminescence show that although the solvent used for deposition strongly affects the molecular organization and net dipole moment, leading to significant variations in the surface coverage and the electronic properties of the perovskite surface, only the presence of adlayers reduces trap-assisted non-radiative deactivation.