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‘Double doping’ semiconductors can make them twice as effective, say researchers from Chalmers University

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Swedish researchers have uncovered a new way to double the efficiency of organic electronics. OLED displays, plastic-based solar cells and bioelectronics are just some of the technologies that could benefit from their new discovery, which deals with “double-doped” polymers.

Doping in organic semiconductors is managed with a so-called redox reaction, where a dopant molecule receives an electron from a semiconductor, increasing the semiconductor’s electrical conductivity. The more dopant molecules the semiconductor reacts with, the higher its conductivity – or at least to a certain limit, after which it begins to decrease.

Now Professor Christian Müller and his team from Chalmers University, together with colleagues from seven other universities, demonstrated that it is possible to move two electrons to every dopant molecule. He says the innovation is not built on some great technical achievement, but it is simply a case of “seeing what others have not seen”.

“The whole research field has been totally focused on studying materials, which only allow one redox reaction per molecule. We chose to look at a different type of polymer, with lower ionisation energy. We saw that this material allowed the transfer of two electrons to the dopant molecule. It is actually very simple,” he said.

And with double doping, the semiconductor becomes twice as effective, enabling further improvements to technologies that so far have proven less competitive. This is especially true for polymers, which don’t conduct current well enough. Doubling their conductivity while using only the same amount of dopant material could bring them closer to commercialisation.

“With OLED displays, the development has come far enough that they are already on the market. But for other technologies to succeed and make it to market something extra is needed. With organic solar cells, for example, or electronic circuits built of organic material, we need the ability to dope certain components to the same extent as silicon-based electronics. Our approach is a step in the right direction,” said Professor Müller.

The team are also looking into electrically-conducting textiles and other applications as growth areas for polymers.

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