Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self-Assembled Monolayer

Current-voltage hysteresis is a major issue for normal architecture organo-halide perovskite

solar cells. In this manuscript we reveal a several Å thick Methylammonium Iodide (MAI) rich

interface between the perovskite and the metal oxide. Surface functionalization via selfassembled

monolayers (SAMs) allowed us to control the composition of the interface

monolayer from Pb poor to Pb rich, which in parallel suppresses hysteresis in perovskite

solar cells. The bulk of the perovskite films is not affected by the interface engineering and

remains highly crystalline in surface normal direction over the whole film thickness. The subnm

structural modifications of the buried interface were revealed by x-ray reflectivity (XRR),

which is most sensitive to monitor changes in the mass density of only several Å thin

interfacial layers as a function of substrate functionalization. From Kelvin probe force

microscopy (KPFM) on a solar cell cross section study, we further demonstrate local

variations of the potential on different electron transporting layers (ETLs) within a solar cell.

Based on these findings we present a unifying model explaining hysteresis in perovskite solar

cells, giving for the first time insight into one crucial aspect of hysteresis and paving the way

for new strategies in the fields of perovskite based opto-electronic devices.