Mimicking plants to improve solar cells
Published in the Advanced Optical Materials journal, their paper “Flower Power: Exploiting Plants’ Epidermal Structures for Enhanced Light Harvesting in Thin-Film Solar Cells” details how the researchers molded the structure of these epidermal cells (using polydimethylsiloxane) before replicating the structure by pressing the mold into optical glue, cured directly onto an organic solar cell.
Prior to this experiment, the researchers at the Light Technology Institute (LTI), the Institute of Microstructure Technology (IMT), the Institute of Applied Physics (APH), and the Zoological Institute (ZOO) of KIT had investigated the optical properties and antireflection effect of the epidermal cells of different plant species. They found these properties particularly evolved in rose petals. Further scrutiny under an electron microscope revealed a disorganized arrangement of densely packed microstructures, which they decided to imprint onto the face of a solar cell.
This seemingly simple pattern transfer resulted in power conversion efficiency gains of twelve percent for vertically incident light and even higher efficiency gains at very shallow incidence angles.
The excellent omnidirectional antireflection properties of the replicated epidermis is not only able to reduce surface reflection to a value below five percent, but each replicated epidermal cell works as a microlense that extends the optical path within the solar cell, increasing the photons’ probability to be absorbed.
The researchers see their findings applicable to any solar cell technology, they also envisage that other plants’ surface properties could be combined into one optimized layer.
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