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Barrier films are required for a number of applications such as food packaging or organic electronics to prevent product degradation results from exposure to water vapour and oxygen. In order to determine the effectiveness of polymers and deposited barrier films to inhibit water permeation, the water vapour transmission rate (WVTR) needs to be measured. The calcium test, MOCON instrument and tritiated water permeation can all be used to determine the WVTR, but the values produced by these techniques have not been extensively compared. The WVTR of two polymer substrates and two barrier films deposited onto polymer substrates have been measured using these three techniques. For a polyethylene terephthalate substrate and a MOCON reference film, similar WVTR were observed for all three techniques. For two commercially available barrier films, variable WVTRs were observed and attributed to film defects. WVTR measurements play an essential role in the use of polymers and barrier films to retard water permeation, therefore an understanding of the advantages and disadvantages of each technique is of great importance.

A comparative degradation study of solar cells based on a bulk-heterojunction (BHJ) blend of poly(3-hexylethiophene) (P3HT) and phenyl [6,6] C61 butyric acid methyl ester (PCBM) with two different cathodes is reported. Poly(ethylene-dioxythiphene):poly(styrene sulfonate) (PEDOT:PSS) coated ITO electrodes were used as the anode, whereas Ca/Al and Ca/Ag electrodes were used as cathodes. Fully degraded devices were subjected to thermal annealing under inert atmosphere. The performance of degraded solar cells with a Ca/Al cathode exhibited no improvement after treatment. However the solar cells with a Ca/Ag cathode exhibited a considerable recovery in their performance following annealing under a nitrogen atmosphere. Indeed, these solar cells could be subjected to many degradation and regeneration cycles. Current density-voltage (J-V) characteristics and X-ray photoelectron spectroscopy (XPS) studies show that this behavior arises from the complex chemical thermodynamics of the reactions that can occur at the cathode/active layer interface. In particular, the recovery of device performance for solar cells with a Ca/Ag cathode is due to the reversible oxidation of Ag upon thermal annealing.