New steps forward for organic photovoltaics
– Improving the performance of a given technology does not always mean aiming to make it perfect. In some cases, imperfections give unexpected results. This is what happens to the efficiency of organic photovoltaic cells, which has always been a weak point for this segment. Professor Dooyoung Ah of Abdullah Gül University in Turkey showed that by inserting small bumps on the flat surface of these cells it is possible to increase the absorption of light by up to 66%. But these are not just any imperfections. As explained in the article published in the Journal of Photonics for Energy, the scientist opted for tiny hemispherical shells, nanometric scale protuberances capable of increasing the absorbed photons and also their “entry points”.
The work still moves on a “virtual” plane, without real prototypes, but the modeling results are equally encouraging.
Efficiency Organic Photovoltaic Cells, today at 19.2%
Increasing the efficiency of organic photovoltaic cells is a fundamental step to spreading the technology on a large scale. The segment is already very economical compared to crystalline silicon cells, with easier integration and an independent supply chain from the Chinese industry. But progress in this area has been much slower than in other segments.
At present the value of conversion of light into electricity higher for organic photovoltaics has marked the Jiao Tong University of Shanghai and is equal to 19.2% (reported in the Best Research Cell Efficiencies Chart of the NREL). As a comparison in the field of organic semiconductors, single junction and without concentrators, the highest value shows a solar cell in GaAs of Alta Device with a nice 29.1% efficiency.
Increasing the efficiency of polymer photovoltaics
In his study, Professor Dooyoung Hah analyzed the absorption spectra within the active hemispherical shell layer, providing a detailed examination of how light interacts with the cell’s structure and materials. In detail, the research focused on a photovoltaic cell composed of organic polymer – the P3HT:ICBA – as an active layer, placed between a transparent top layer of indium tin oxide of aluminum and an aluminum bottom layer. All this “resting” on a substrate of PMMA. This sandwich organization has been maintained in all nanoshells created on the surface.
The analysis showed that the structure of the mini bumps when subjected to transverse electric polarized light (TE), determines an increase of 66% in light absorption compared to flat structure devices. Similarly, for transverse magnetic polarized light (TM), an increase of 36% is observed.
“Thanks to improved absorption and omnidirectionality – commented Hah on Spie.org – the proposed hemispherical shell-shaped active layers will prove useful in various areas of application of organic solar cells, such as biomedical devices, as well as applications such as windows for power generation and greenhouses, Internet of things and so on”.