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 entitled "Optimization of interfaces in encapsulated organic PV systems." The defense will take place at 2:00 p.m. in Room A of the IUT de Chambéry on the Bourget-du-Lac campus.
Thesis summary
In order to limit degradation by moisture and oxygen in flexible organic photovoltaic devices, solar cells are encapsulated between gas barrier films. Despite the importance of encapsulation processes and their potential impact on the initial performance and aging of devices, they are rarely studied in the literature. In addition, several field aging studies have shown that mechanical deterioration limited the lifetime of samples well before their photochemical stability was compromised. Adhesion between the different layers comprising the cells is therefore a critical factor in obtaining reliable flexible devices after their implementation and during their 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 in the samples, the mechanical characterization technique of 180° peel testing was adapted and then applied to the flexible devices. In addition, non-destructive imaging techniques were developed to characterize the devices: laser beam induced current mapping (more commonly known by the acronym "LBIC") and optical and electrical excitation luminescence imaging. Thanks to these techniques, the hypothesis of mechanical degradation of the devices during the roll-to-roll encapsulation process was put forward. Solutions to improve the interfaces identified as mechanically weak were sought and then evaluated in relation to the photovoltaic performance of the reference devices. The imaging techniques developed previously were also applied during accelerated aging of the encapsulated cells. A mechanism was proposed to explain the spatial location of the degradation as well as the type of degradation, optical or electrical, that occurred at each stage of aging.