Aluminum Electrode Insulation Dynamics via Interface Oxidation by Reactant Diffusion in Organic Layers

摘要

Appreciable progress has been achieved in the development of organic photovoltaics(OPV) over the last decade. However, further improvement of operationalstability remains a challenge. In this contribution, focus is placed on corrosionand delamination of the metal contact, which are mainly caused by oxygen orwater vapor ingress but in other cases also via mechanical wear and differentthermal expansion coefficients. So-called pinholes and electrode edges providepathways for ingress of water vapor and oxygen, which may attack the metal–organic interface. Thus, electrical insolation via formation of insulating metal oxideand concomitant mechanical delamination occurs. As charge injection andextraction is suppressed at insulated and delaminated areas, the active areacontributing to power conversion gets reduced. This work links analytical andnumerical predictions about the active area in contact with the electrode toexperimentally observe dependencies. Spatially and time-resolved electroluminescencemeasurements provide information on location, size, and growth-rate ofinsulated areas. Area loss rates for dark spots depend either sub-linear (for earlystages and edge-ingress) or linear (later stages) on time. The initial defect sizehas a clear impact on growth rates. Furthermore, it has possible to demonstratetitanium oxide interlayers to slow down this type of extrinsic degradation.