On Thursday, April 5, 2018, Sacha Juillard, PhD student in Materials, Mechanics, Civil Engineering and Electrochemistry at the Laboratory of Electrochemistry and Physicochemistry of Materials and Interfaces (LEPMI), will defend his thesis "Optimization of the interfaces of encapsulated organic PV systems". The defense will take place at 2pm in room A of the Chambéry IUT on the Bourget-du-Lac campus.
Summary of the thesis
In order to limit moisture and oxygen degradation of flexible organic photovoltaic devices, solar cells are encapsulated between gas-barrier films. Despite the importance of encapsulation processes and their potential impact on initial performance and device aging, they are rarely studied in the literature. What's more, several field aging studies have shown that mechanical deterioration limits the lifetime of samples long before their photochemical stability is called into question. Adhesion between the different layers making up the cells is therefore a critical factor in obtaining reliable flexible devices after processing and during use. In this work, two encapsulation processes were studied: roller lamination of a pressure-sensitive adhesive and vacuum lamination of a thermoplastic. In order to quantify the adhesion of each of the interfaces included in the samples, the 180° peel mechanical characterization technique was adapted and then applied to the flexible devices. In addition, non-destructive imaging techniques were developed for device characterization: laser beam induced current mapping (LBIC) and luminescence imaging under optical and electrical excitation. Thanks to these techniques, the hypothesis of mechanical degradation of the devices during the roller lamination encapsulation process has been put forward. Solutions for improving the interfaces identified as mechanically weak were sought and then evaluated against the photovoltaic performance of reference devices. Imaging techniques developed previously were also applied during accelerated aging of encapsulated cells. A mechanism was proposed to explain not only the spatial location of degradation, but also the type of degradation - optical or electrical - occurring at each stage of aging.