Organic polymer breakthrough

Researchers at UC Santa Barbara’s Center for Polymers and Organic Solids (CPOS) claim to have made significant advances in the creation of organic polymers for plastic solar cells.

The team, led by Prof Guillermo Bazan, said that it had reduced the reaction time of the polymers by 99 per cent, from 48 hours to 30 minutes. The researchers claim that this could cut the production time for organic polymers by half.

In addition, the team has increased the average molecular weight of the polymers by a factor of three. According to the researchers, the higher molecular weight could potentially increase the current density of plastic solar cells by a factor of four.

Publishing their findings in Nature Chemistry online, the researchers said that the increase in current density was found to be approximately proportional to the increase in average molecular weight.

The changes have been the result of a number of modifications, including replacing conventional thermal heating with microwave heating, changing the reactant concentrations and varying the ratio by five per cent from the nominal 1:1 stoichiometric ratio normally employed in polymerisation reactions.

Bazan said the work would greatly accelerate research in this area by making possible the rapid production of different batches of polymers for testing. ‘We plan to take advantage of this approach both to generate new materials that will increase solar-cell efficiencies and operational lifetimes, and to re-evaluate previously considered polymer structures that should exhibit much higher performance than they showed initially,’ he added.

Mike McGehee, director of Stanford University's Center for Advanced Molecular Photovoltaics, said: ‘Many synthetic chemists around the world are making copolymers with alternating donor and acceptors to attain low band gaps. Most of them are having trouble attaining adequate molecular weight, so this new synthetic method that creates longer polymer chains is a real breakthrough. The reduction in synthesis time should also make it easier to optimise the chemical structure as the research moves forward and will ultimately reduce the manufacturing cost.’