Some Aspect of the Stability of Flexible Organic Solar Cells
Emilie Planes a, Lara Perrin a, Manon Spalla a, Muriel Matheron b, Solenn Berson b, Lionel Flandin a
a Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, France, Grenoble, France
b Univ. Grenoble Alpes, CEA, LITEN, INES, France, Le Bourget-du-Lac, Francia, Le Bourget-du-Lac, France
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Tsukuba-shi, Japan, 2020 January 20th - 22nd
Organizers: Michio Kondo and Takurou Murakami
Oral, Lara Perrin, presentation 037
Publication date: 14th October 2019

The stability of final setups is one of the prominent challenge for photovoltaic applications. There is thus a vital need for a better understanding of the degradation mechanisms and thereby the possible mitigation strategies. Flexible organic photovoltaic (OPV) modules are commonly encapsulated by two gas-barrier films to prevent moisture and oxygen degradations. Although this encapsulation process can significantly be diversified, its effect on both initial and in-use performances are scarcely described in the literature. In addition, several on-site studies showed that the mechanical degradation could be more critical on optoelectronic effects than the photo-chemical counterpart. It seems that the stability of the overall complex device architecture may be altered according to several very dissimilar mechanisms: 1- within the active components, 2- at the layers’ interfaces and 3- from the external envelop. Presented work focuses on the last two scales using different ageing conditions (in inert atmosphere, and in severe 85°C/85%RH conditions). For this purpose, two variants in the encapsulation process are compared: the roll-to-roll lamination of a pressure sensitive adhesive and the vacuum lamination of a hot-melt thermoplastic.

The adhesion between the different layers within the device is a key factor for the development of flexible OPV devices reliable after all the processing steps, and during in-use. We here propose a way to individually quantify the adhesion strength of each interface in samples. The 180° peeling test mechanical characterization was adapted for and then applied to the flexible devices. In addition, non-destructive imaging characterization techniques were developed: the laser-beam induced-current mapping, and the luminescence emission imaging under optical and electrical excitation. These latter techniques largely confirmed the hypothesis of a mechanical degradation during the roll-to-roll lamination process.

All these investigations revealed two weak interfaces and several methods have been tested to try and enhance them. We show that improving these interfaces directly increases both the overall performance of the device, and its resilience to roll-to roll encapsulation. Using the imaging techniques previously developed, we will finally study the stability of the encapsulated OPV devices during accelerating aging tests in inert atmosphere at 85°C and 85°C/85%RH. An occurring aging mechanism was proposed, which allows one to explain the localization of the degradation but also the failure type, either optical or electrical.

The conseil Savoie Mont Blanc for financial support.

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