Light absorption enhancement and electronic properties of thin-film solar cells

In this work we developed several strategies to enhance solar cells which lead to stronger sunlight absorption with less active material and thereby also reducing costs. This is accomplished through utilizing nanoscale architectures, which geometry can be tailored to modify the flow of light for optimal absorption. Since sunlight comprises of photons with a broad range of wavelength (colors), ensuring a complete absorption requires sophistications in the nanostructure design due to its wavelength dependent interaction with light. To address this challenge we utilized combinations of different periodic nanostructures with one another and also with disordered rough light diffusers. Aside from our absorption enhancement work, we also investigated light emission enhancement utilizing periodically placed metal nanoantennas. We demonstrate how hybrid plasmonic-photonic modes that arise in such system can be used to control and enhance emission over an extended spatial region. This is relevant in solar cell enhancement schemes which convert the unused portion of sunlight into the color range suitable for optimal usage. Having investigated various light management schemes to enhance solar cells, we proceeded to examine the limiting factors which hinder efficient electrical current extraction from polycrystalline silicon thin film solar cells of a few micrometers thick. We identified the conditions in which this more economical material gives the desired solar cell performance

Tuning of nanophotonic and nanoplasmonic components with liquid crystals

Due to the strong electro-optic effect of liquid crystals, their refractive index can be modified by using relatively small voltage signals. This effect has been exploited in many configurations to tune the properties of optical components. In the past few years this tuning effect has been demonstrated with optical components with nanometer-scale size. The optical tuning is not only interesting to modulate the propagation of light, but also to tune the emission of light

Dual-interface grating supercelles for broadband absorption

Here, we propose the usage of dual-interface grating (DIG) supercells with multiperiodicity as shown in Fig. 1(c) and numerically study their extensive mode-coupling possibilities. We consider a-Si solar cell systems which have active layer thickness that is comparable to the size of the grating geometry. At such thickness regime, the grating structure heavily affects the eigenfield profiles of the guided modes. We show how DIG supercells offer much possibility in improving higher order diffraction coupling conditions to guided modes, while maintaining lower order diffraction coupling efficiency. In addition, including symmetry-breaking or blazing properties in DIG structures can lead to excite previously inaccessible modes efficiently, and thus further broadens the enhancement range

Dual-interface gratings for broadband absorption enhancement in thin-film solar cells

We numerically study complex dual-interface grating systems to enhance absorption efficiency in thin-film silicon solar cells. We combine a plasmonic grating at the back side of the solar cell with a dielectric grating at the front side of the cell. We show a proof of principle, with one-dimensional gratings, that the distinctly different nature of the gratings can provide complementary enhancement mechanisms, which we further exploit by tailoring the specific periodicities, and by introducing blazing. Having different periods at specific interfaces allows for more efficient diffraction into both plasmonic and dielectric guided modes. In addition, grating specific blazing exposes extra modes to normal incident light through symmetry breaking. Multiple optimization routes are possible depending on the choice of photonic phenomena

Angle insensitive enhancement of organic solar cells using metallic gratings

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Combining front and back grating structures for broadband absorption enhancement in thin-film silicon solar cells

We investigate the possibilities of enhancing absorption in thin-film silicon solar cells with grating structures on the front ITO and back Ag contacts simultaneously. Broadband enhancement from complementary effects of each grating is demonstrated

Plasmonic absorption enhancement in organic photovoltaics

Organic solar cells have a strong potential for the near future, because their material and fabrication costs can be much smaller than for traditional technologies. However, in order to become commercially viable their efficiency needs to increase. One of the novel, interesting techniques to increase the light absorption is by including plasmonic enhancements. These metallic features instigate strong, local resonances which trap the light in the very thin layers. In this work we report rigorous numerical investigations of organic cells with embedded metallic nanoparticles and with patterned metallic electrodes. The state-of-the-art material P3HT:PCBM is employed as the active layer. We show that in both cases, with particles or with patterned electrodes, a strong enhancement is achievable, with roughly an increase of up to 50% in the solar light absorption. Such enhancements could prove crucial for more efficient energy devices