Water and oxygen, main enemies of organic solar cells

Researchers from the Rey Juan Carlos University (URJC) (Spain) analyze the impact of exposure to different atmospheric conditions. The results provide relevant data for the design and manufacture of new devices with low-cost techniques.

Solar cells based on organic materials have many advantages over conventional silicon cells. They are lighter, semi-transparent and have reduced thicknesses. In addition, they can be manufactured in flexible substrates, such as Polyethylene terephthalate (PET), a plastic widely used in bottle packaging, and with low-cost technologies. However, these cells degrade more easily than traditional cells.

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In this study, Belén Arredondo, researcher of the Electronic and Photonic Organic Devices Group of the URJC, along with researchers from the National Physical Laboratory of England and the Technical University of Denmark participated. In this work, we have analyzed the degradation in different atmospheres of flexible organic solar cells manufactured using the low cost ‘roll-coating’ technique. For this purpose, these devices have been characterized using the impedance spectroscopy technique in order to determine the different mechanisms that degrade them: only water, only oxygen, and water plus oxygen.

The results of this research have recently been published in the scientific journal Solar Energy Materials and Solar Cells. This article concludes that oxygen and water degrade cells differently. “On the one hand, the absorption and diffusion of oxygen in the cell introduces defects that dramatically decrease the photogenerated current through the cell. In addition, the interaction with oxygen increases the electrical resistance of some layers of the cell, “says Belén Arredondo. On the other hand, the researchers have observed that in the structure of the cells exposed to water, energy barriers appear that worsen the response of the current and the voltage at the point of maximum power. As a result, the efficiency of the cell decreases.

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Determining the mechanisms of degradation is essential to design a manufacturing process for solar cells that take these factors into account and minimizes them. “This study has special relevance because flexible cells have been used that could adapt to surfaces with different shapes and manufactured with low-cost techniques,” adds the researcher at the URJC. This type of cells has potential applications in portable devices, small and low consumption such as, for example, calculators, laptop or mobile cases.