Dopant boost could double efficiency of organic solar cells

January 21, 2019 //By Peter Clarke
Dopant boost could double efficiency of organic solar cells
Researchers have discovered a technique that can double the number of electrons made available by doping plastic materials, thereby doubling the materials efficiency. Double doping could improve the light-harvesting efficiency of flexible organic solar cells, the switching speed of electronic paper, and the power density of piezoelectric textiles.

The technique has implications for organic electronics, OLED displays and plastic display back-planes, plastic solar cells and bioelectronics.

Doping is an essential part of making organic materials into semiconductors and operates by a reduction-oxidation process in that the dopant molecule receives an electron from the semiconductor. The more dopant molecules that the semiconductor can react with, the higher the conductivity, up to certain limits. Up until now dopant molecules have only exchanged a single electron.

A team led by Professor Christian Müller at the Chalmers University of Technology, Sweden and including colleagues from six other universities have been able to demonstrate it is possible to move two electrons to every dopant molecule. Specifically, common p-type dopants can accept two electrons per molecule from conjugated polymers with a low ionization energy.

The work was carried out in collaboration with colleagues from Linköping University (Sweden), King Abdullah University of Science and Technology (Saudi Arabia), Imperial College London (UK), the Georgia Institute of Technology and the University of California, Davis (USA), and the Chemnitz University of Technology (Germany). What the implications are for choice of polymers for organic implications remains to be seen.

"The whole research field has been totally focused on studying materials, which only allow one redox reaction per molecule," said Professor Müller, in a statement. "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."

The work has been published in Nature Materials .

Professor Müller made the point that the ability to double organic electronic efficiency could improve applications that are already commercial but also allow new applications that have previously been non-viable. Organic solar cells and organic logic circuits are two examples.

The research group at Chalmers is looking in to the development of electrically conducting textiles and organic solar cells.

Double doping of conjugated polymers with monomer molecular dopants

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