Screening organic materials to find the most efficient candidates for photovoltaic cells has always been difficult but may soon be easier thanks to a new spectroscopic technique, Japanese researchers say.

Although organic solar cells show significant potential as energy conversion solutions because of their flexibility and the low-cost of production, one hurdle to their widespread adoption is the complexity of the processes involved in their power conversion processes, the researchers say.

At the heart of the problem is that their energy conversion involves two separate steps, first the formation of a charge and then the energy transport process.

Researchers at Japan's University of Tsukuba have reported in the journal Applied Physics Letters that they've created a method to determine the efficiency of the charge formation in an organic photovoltaic material.

The technique involved a combination of two different types of spectroscopy; electrochemical spectroscopy and photo-induced spectroscopy.

"By qualitative analysis of the spectral change, we can deduce how many charges are produced by one photon -- its charge formation efficiency," says Yutaka Moritomo of the university's Institute of Materials Science.

The spectroscopic technique will enable quick and efficient screening and testing  of organic materials for new organic photovoltaic cells that could power many devices, he says.

"Organic materials have several requirements -- including high charge formation efficiency and high charge transport efficiency -- so our method can be used to quickly screen the materials by charge formation efficiency," he says.

This could lead to cheaper and more efficient solar cells, because once identified, an organic polymer -- a plastic -- can be produced in high volumes with low production costs.

Such a material would also possess a high optical absorption coefficient, meaning a small amount of the material would be capable of absorbing a significant amount of light for conversion into electrical energy.

Because photovoltaic cells utilizing organic polymers are flexible, as opposed to inorganic-based solar cells that are rigid, they can be incorporated into objects and devices where rigid cells are not feasible, or used over large areas of irregular surfaces.

Solar cells made from inorganic material such as silicon are expensive to produce, whereas plastic-based photovoltaic cells could be produced in vast numbers at much less cost.

While their efficiency is not yet up to the levels of conventional silicon-based solar cells, advances such as those provided by the Japanese team could lead to organic photovoltaics becoming a much more attractive clean energy option. 

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