The barrier effectMichael Corazza
Some layers show the special ability of acting as a barrier. Specific properties can make a material block for example water flow and prevent the diffusion of particles throughout the cell, thus causing degradation. An experiment by Madsen et al.DOI:10.1117/1.3544010 investigated the concentration of water and oxygen at the different layer position of a solar cell with time-of-flight secondary ion mass spectroscopy. The structure of the cell was glass/ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag/encapsulation. The main conclusions were that oxygen decreases almost constantly with addition the number of layers that it has to go through, while water decreases drastically after the layer of P3HT:PCBM, which acts as a powerful barrier layer against water diffusion.
It is important to understand the blocking properties of a material. The adding of a layer to the cell structure may reduce diffusion of aging factor, thus increasing the lifetime. However, the layer must also allow an optimal working condition for the cell, which means that the electrical behavior should not be deteriorated.