Organic semiconductors explored at UBC

In a recent publication in Nature Communications, UBC researcher Katherine Cochrane examined the fundamental properties of organic semiconductors.

Semiconductors are elements on the periodic table that conduct electricity better than nonmetals but not as well as metals. One of the most common semiconductors is silicon, which conducts electricity via exposure to light and is used in solar cells as well as other types of electrical components.

Organic semiconductors are essentially semiconductor cells composed of carbon based materials, called organics. Since organic materials don't normally conduct electricity well, organic cells require an interface between two different organic materials in order to generate an electrical charge.

“What happens is that [electrons] have to diffuse to where two types of materials meet each other at an interface and then there’s charge transfer. Then you've got ... [a] current flowing,” said Cochrane.

Cochrane’s current research involves examining the specific molecular interactions that happen in the interfaces of organic semiconductors through scanning tunnelling microscopy — using a special microscope to image surfaces of tiny structures. She said that, since scientists currently have limited knowledge in this particular area, her goal is to determine the how interfaces can yield the most effective results.

“What I want to do is look at the actual molecules and place two molecules next to each other and see how the geometry affects the electronic structure,” said Cochrane.

Cochrane said that one advantage of organic semiconductors is that its manufacturing process is more cost-effective compared to traditional semiconductors like silicon. 

“If you’re making a silicon cell, you need to have a very clean environment and high temperatures. The cost of making these — both in actual dollars and in energy — can be quite high,” said Cochrane. 

With organic cells, production can be as simple as inkjet printing the material through refabricated newspaper printing presses. Organic semiconductors also offer the advantage of being lighter compared to silicon.

Still, Cochrane says that organic cells are not a replacement for silicon. One of the limitations of organic semiconductors are their efficiency. Organic cells only have a maximum efficiency of 14 per cent while silicon cells have a maximum efficiency as high as 40 per cent.

Experts don't want to replace silicon with semiconductors, explained Cochrane. Instead, research is looking into using organic semiconductors in places where silicon can't be used.

Organic semiconductors are presently available for commercial use. Some devices —including televisions and mobile phones – currently operate on organic cells.