The processes of plants are becoming promising systems for researchers to emulate to improve methods for generating and storing solar energy. We’ve already told you how engineers have mimicked photosynthesis to create a new method for solar-energy storage and a bionic leaf that turns solar energy into liquid fuel. Now scientists at the Karlsruhe Institute of Technology (KIT) in Germany have reproduced cells in rose petals to create an organic solar cell with higher energy efficiency.
Specifically, a team from KIT has replicated the epidermal cells in the outermost tissue of rose petals that have particularly good antireflection properties, they said. They then integrated the transparent replicas into the front of a solar cell to achieve a relative efficiency gain of 12%.
The researchers -- which worked with scientists at the Center for Solar Energy and Hydrogen Research Baden-Württemberg -- published an article about their work in the journal, Advanced Optical Materials .
Solar cells use a method not unlike photosynthesis to generate electricity from solar energy -- light is absorbed and converted into a different form of energy. In this process, it is important to use as large a portion of the sun's light spectrum as possible and to trap the light from various incidence angles as the angle changes with the sun’s position.
After studying rose petals, researchers concluded that their strong antireflection properties could be conducive to achieving this goal, said researcher Guillaume Gomard, group leader of Nanopothonics at KIT’s Light Technology Institute. After observing the epidermis under a microscope, researchers noticed that it consists of a disorganized arrangement of densely packed microstructures, with additional ribs formed by randomly positioned nanostructures.
To replicate this over a large area, the team transferred it to a mold made of polydimethylsiloxane, a silicon-based polymer, and then pressed the resulting negative structure into optical glue. They then left the glue to cure under a UV light. The method “creates microstructures of a depth and density that are hardly achievable with artificial techniques” in an easy and cost-effective way, Gomard said.
Scientists then integrated this transparent replica into an organic solar cell, where power conversion efficiency gains of 12% resulted for vertically incident light. At very shallow incidence angles, the efficiency gain was even higher, according to the team. The reason for the gain is the omnidirectional antireflection properties of the replicated epidermis, which could reduce surface reflection to a value below 5%, even for a light incidence angle of nearly 80 degrees, researchers said.
Another reason the addition of the replicated epidermis showed such efficiency gain is every single replicated epidermal cell works as a micro lens, according to researchers. This effect works in three ways to improve light absorption, they said. It extends the optical path within the solar cell, enhances the light-matter-interaction, and increases the probability that the photons will be absorbed.
Gomard said the research is applicable to both other plant species as well as other photovoltaic technologies. “Since