UK breakthrough promises solar and OLED gains

In a discovery that could improve the efficiency of organic solar cells and OLED displays, scientists at Swansea University have devised a method to identify ‘charge traps’ in organic semiconductors.

Lead author, Nasim Zarrabi measuring the photo-response of organic solar cells at Optoelectronics Laboratory of Swansea University (Credit: Swansea University)

Made from carbon and hydrogen, organic semiconductors are the key components in OLED screens and organic solar cells. It had previously been assumed that charge traps within the semiconductor layer of organic cells were limiting the performance of the devices, but until now the tiny signatures of these traps had not been found. The work is published in Nature Communications.

“For a long time, we guessed that some charges that are generated by the sunlight can be trapped in the semiconductor layer of the solar cell, but we’ve never really been able to prove it,” said lead author Nasim Zarrabi, a PhD student at Swansea University.

“These traps make solar cells less efficient, photodetectors less sensitive and an OLED TV less bright, so we really need a way to study them and then understand how to avoid them – this is what motivates our work and why these recent findings are so important.”

While the discovery itself will not directly improve the performance of organic solar cells and OLED displays, it will provide the basis for further research into charge traps and how they might be harnessed in the future to deliver gains. According to Dr Oskar Sandberg, the theorist behind the work, the type of experimental accuracy outlined in the study has been anticipated by him and others across the scientific community for several years.

“What we observed experimentally has been known in silicon and gallium arsenide as intermediate band solar cells, in organic solar cells it has never been shown that traps can generate charges,” said Dr Sandberg.

“The additional charges generated by the traps is not beneficial for generating lots of electricity because it is very tiny. But it is sufficient to be able to study these effects and maybe find ways to control them in order to make genuine improvements in device performance.”