Al 2 O 3 ‐Atomic Layer Deposited Films on CH 3 NH 3 PbI 3 : Intrinsic Defects and Passivation Mechanisms

The initial interaction of atomic layer deposited films of Al 2 O 3 at room temperature on CH 3 NH 3 PbI 3 (MAPI) films is studied. Synchrotron radiation–based photoelectron spectroscopy is applied to analyze the initial changes in the Al‐derived features by comparing samples with different Al 2 O 3 film thicknesses. It is found that polarons and excitons, both intrinsic defects of Al 2 O 3 , play a key role in the interface formation. The polaronic states uptake a charge from the MAPI substrate. This charge is transferred to and stabilized in the excitonic state of Al 2 O 3 which is assigned to predominately tetrahedral coordinated Al sites. This charge transfer is initiated by vacancies present in the MAPI substrate and stabilizes a covalent bonding at the Al 2 O 3 –MAPI interface but also causes a roughening of the interface which may lead to the formation of grain boundaries. On top of the rough interface, 2D Al 2 O 3 clusters with an increasing number of octahedrally coordinated Al—O bonds grow, and with increasing Al 2 O 3 coverage, they introduce self‐healing of the structural defects.