Plasmonic Organic Solar Cell

The multidisciplinary project Plasmonic Organic Solar Cells (PLASMOSOL) embraces the fields of nanophotonics, materials research and optoelectronic devices. It particularly focuses at research in plasmonic light trapping schemes for organic solar cell technology with improved efficiency. It aims at investigation of new metallic nanostructures exhibiting unique plasmonic characteristics for collecting of incident light intensity over broad wavelength and angular ranges and its concentrating at absorber region in thin film organic solar cell architectures. It brings together complementary teams pursuing research in plasmonics (lead by Dr. Jakub Dostalek), materials for photovoltaic technologies (lead by Dr. Theodoros Dimopoulos) at Austrian Institute of Technology (AIT) with the group of Ao.Univ.-Prof. Dr. Emil J. W. List at NanoTecCenter Weiz Forschungsgesellschaft (NTCW) operating in the field of organic optoelectronic devices. The goal of this project exploration of new generic plasmonic light trapping schemes that will be applied for broad range of polymer OSC and enable advancing their efficiency over 10 %. In the first phase of the project, two complementary types of plasmonic light trapping concepts will be theoretically and experimentally investigated: A) multi-diffractive elements utilizing nano-imprint lithography (NIL) and B) arrays ZnO nanowire electrodes decorated with metallic nanoparticles. In the second stage of the project C), series of model devices with and without implemented plasmonic structures will be developed and fully characterized in order to correlate their performance with the properties of the plasmonic structures and to compare with current state-of-the-art solar cells.

The project Plasmonic Organic Solar Cells (PLASMOSOL) aimed at the development of optical nanostructures that are tailored to enhance the efficiency of thin film organic solar cells (OSC). Generic approaches with the potential for applications in a broad range of common polymer OSCs were in the focus of interest. The project was jointly pursued by complementary research groups with background in nanophotonics, materials research and optoelectronic devices at Austrian Institute of Technology and NanoTecCenter Weiz Forschungsgesellschaft. The latter partner has merged during the duration of the project with Joanneum Research. In the first phase of the project, an optical design for plasmonic broadband light trapping at thin films has been carried out. The related structures were based on periodic multi-diffractive metallic elements deployed at transparent or metallic electrodes. In order to be able to structure sufficiently large areas of OSCs, laser interference lithography (LIL) and nano-imprint lithography (NIL) were adopted for the preparation of arrays of metallic nanoparticles, nanowires, and relief corrugations. Simulations supported the design of the structures and the interplay of light trapping via surface plasmons and dielectric waveguides predicted > 30 per cent enhancement of the integral absorption in the active layer for exemplary solar cells based onP3HT:PCBMIn the second phase of the project, series of OSC devices were prepared and characterized in order to correlate their performances with the properties of the plasmonic structures and to compare them with current state-of-the-art solar cells. Investigated solar cells comprised relief gratings at the metallic electrode of P3HT:PCBM based layer architecture. Solar cells with inverted and normal geometry were prepared and NIL was adopted for the structuring of their silver or aluminum electrodes. The light trapping (particularly at wavelengths red shifted with respect to the P3HT:PCBM absorption band) gave reason for an enhancement in external quantum efficiency (EQE), but not for a significantly improved short circuit current Isc, and therefore also not for enhanced solar cell efficiency. This effect is assumed to be caused by the fact that the generation of the short circuit current is still dominated by the absorption characteristic of the P3HT:PCBM blend, regardless of the enhancements observed in EQE characteristics. In summary, the project provided valuable design rules and insights to the optical light trapping in thin film solar cells devices, but did not reach its goal of enhancing the efficiency of organic solar cell technology. The project supported three PhD theses and its results were published in 2 papers in peer reviewed journals and 7 additional papers that are currently in preparation, 7 presentations at scientific conferences and 2 conference proceeding papers.