Silicon remains the material to beat when it comes to creating a semiconductor but, in recent years, there have been a number of investigations into what other materials out there offer an alternative.

As part of that search, a team from Oregon State University has published the findings of a study that indicates the incredible power of an organic pigment, the hidden capabilities of which have escaped humans for hundreds of years.

According to the research team, this pigment is called xylindein and has remained a popular shade in the staining of wood to create a blue-green colour.

The xylindein pigment is secreted by two wood-eating fungi in the Chlorociboria genus. When it is used as a pigment, it is so stable that decorative products made half a millennium ago still exhibit its distinctive hue.

In fact, it has even been shown capable of withstanding prolonged exposure to heat, ultraviolet light and electrical stress.

With such capabilities, the research team wanted to see whether xylindein could be used as a semiconductor. These tests showed it to be good, but not exactly great.

Mysterious properties

With current fabrication techniques, xylindein tends to form non-uniform films with a porous, irregular, ‘rocky’ structure that hinders its semiconducting abilities. But there is underlying promise that a great semiconductor is to be found somewhere beneath the surface.

By blending xylindein with a transparent, non-conductive polymer called polymethyl methacrylate, the researchers were able to compare a pristine xylindein solution with this new blend.

They found the non-conducting polymer greatly improved the film structure without a detrimental effect on xylindein’s electrical properties. Also, the blended films actually showed better photosensitivity, but why this is remains a mystery.

“Exactly why that happened, and its potential value in solar cells, is something we’ll be investigating in future research,” said physicist Oksana Ostroverkhova.

“Xylindein will never beat silicon but, for many applications, it doesn’t need to beat silicon,” she said. “It could work well for depositing onto large flexible substrates, like for making wearable electronics.”

Colm Gorey
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