Mother Nature shows how to improve solar technology.

Yang, N, Y Zhang, J Halpert, J Zhai, D Wang and L Jiang. Granum-Like stacking structures with TiO2 –graphene nanosheets for improving photo-electric conversion. Small http://dx.doi.org/10.1002/smll.201200079.

Synopsis by Marty Mulvihill, Aug 01, 2012

Researchers have improved solar cell performance by looking to leaves. The prototype mimics a leaf’s chemical layers that catch the sunlight and send the energy to plant cells. The bio-inspired solar cells were 20 times better at creating electricity than traditionally designed solar cells made from the same materials.

Solar power is an attractive energy source because it is free, readily available, clean and sustainable. To tap into this rich resource, solar power cells installed on roofs and in deserts capture and convert light to energy. But current types of cells remain inefficient and costly.

Researchers have been trying for more than two decades to build better cells by mimicking plants’ ability to harness the power of sunlight. Plants – through photosynthesis – naturally do this.

The layered design is unique because it takes advantage of an often overlooked leaf architecture that improves the efficiency of energy conversion. The results of the Chinese study are published in the journal Small.

Leaves have a specialized, layered structure called a granum, which collects light from the sun and turns it into energy the plant can use. The researchers identified two key features of the granum that could help improve solar cells: a stacked structure and a design to efficiently transfer energy.

Inside a plant granum are thin alternating layers of pigment molecules that absorb the light and molecules that turn the sun’s rays into electrical energy then used in chemical reactions. The researchers modeled their solar cell on this design. They created alternating layers of titanium dioxide – which absorbs the light, and graphene – which transports the energy.

The addition of graphene to solar cell design allows more efficient transport of the energy away from the titanium dioxide. When the graphene layers were not used, much of the energy absorbed by the titanium dioxide was lost before it could be captured as electrical energy.

Since the graphene layers improve transport of electrical energy, the researchers used many more layers of titanium dioxide, collected more light and increased the amount of light collected.

The results show the alternating, layered structure found in a plant’s granum can improve the performance of solar cells. The design has not been tested in a full-scale solar cell device. More work needs to be done to improve the safety and efficiency of the synthesis process before solar cells based on this technology could reach the market.

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