It has been common to believe that efficient operation of organic solar cells requires a large driving force, which limits the efficiency of organic solar cells.
Now researchers led by Feng Gao, lecturer at IFM at LiU, He Yan at the Hong Kong University of Science and Technology, and Kenan Gundogdu at the North Carolina State University, have published research that show they developed organic solar cells with a significantly lower driving force and faster charge separation than previous cells. The results have been published in Nature Energy.
This implication of this research outcome is that the intrinsic limitations of organic solar cells are no greater than those of other photovoltaic technologies, bringing them a step closer to commercialisation.
The researchers said that when photons emitted by the sun are absorbed by organic semiconductors, strongly bound excitons (rather than free carriers) are generated. The driving force is, to put it simply, a measure of the energy that is used to split the excitons into free carriers. The driving force results in the loss of the photovoltage, a key parameter for the solar cell. The lower the driving force, the higher the photovoltage.
Traditionally, efficient organic solar cells are usually composed of semiconducting polymers and carbon balls known as 'fullerene'. In that case, a large driving force over 0.3 eV is usually needed for efficient charge generation. In the present work, the researchers have replaced fullerene with a semiconducting small molecule, and found that that a low driving force is needed for efficient operation of the devices.
Feng Gao, together with his LiU colleagues, including Professor Olle Inganäs, Professor Fengling Zhang, postdoc Jonas Bergqvist and PhD student Deping Qian, describes in the article solar cells with an energy efficiency of 9.5%.
Feng Gao, said, "We have developed a system with a huge potential to increase the power conversion efficiency in organic solar cells."
Jing Liu | Shangshang Chen | Deping Qian | Bhoj Gautam | Guofang Yang | Jingbo Zhao | Jonas Bergqvist | Fengling Zhang | Wei Ma | Harald Ade | Olle Inganäs | Kenan Gundogdu | Feng Gao | He Yan
Nature Energy 1, Article number: 16089 (2016) | doi:10.1038/nenergy.2016.89
Received: 14 January 2016 | Accepted: 24 May 2016 | Published online: 27 June 2016