While organic photovoltaics (OPV) have demonstrated considerable progress during the past decade in terms of efficiency and cost reduction, sufficiently long life times are still achieved solely by relying on cost-prohibitive packaging materials. It is well documented that environmental contaminants such as oxygen and moisture are primary sources of OPV device ageing due to the native sensitivity of the semiconductor and adjacent functional layers. To synchronize efficiency and stability it is essential to unambiguously identify the underlying degradation mechanisms leading to early performance loss.
Here we demonstrate how a combination of non-destructive imaging modalities can be employed for analyzing and predicting events that lead to device failure. We first discuss the long-term photovoltaic stability of encapsulated OPVs under controlled temperature and moisture settings using an Arrhenius model. Using lock-in imaging detection we visualized the kinetics of moisture ingress and consequent active area loss. By comparing the results of electroluminescence imaging, lock-in thermography, and photoluminescence mapping we conclude that water ingress occurs through the adhesive and that the reaction of water at the active layer interface is most likely the dominant cause for long-term device failure.
Based on our experimental findings, we used classical diffusion theory to quantify moisture diffusion through packaged OPV devices. We verified the kinetics of moisture diffusion independently by tracking water ingress with spatially resolved FTIR spectroscopy. Our findings may inform new strategies for early prediction of moisture and oxygen induced device performance loss in OPV cells and modules.