Mikhail Omelyanovich

Multifunctional stretchable metasurface for the THz range

In this paper we propose and study some electromagnetic properties of a thin composite layer formed by metal stripes of resonant length located on two sides of an elastic polymer film. We show that in the THz range the structure offers multiple functionalities such as high sensitivity to applied mechanical strain and polarization transformation properties. We suggest a method of fabrication for such composite layers, prepare the experimental sample and measure the dependence of the transmission coefficient on stretching.

Perfect plasmonic absorbers for photovoltaic applications

Thin-film photovoltaic (PV) cells enhanced by lighttrapping structures (LTSs), capable to prevent both reflection from the cell and parasitic transmission through its PV layer [1] have not yet been adapted by the industry in spite of rather long history of corresponding research started by work [2]. Perhaps, this is so due to the lack of efficiency of suggested LTSs and/or impractical design solutions in the cases when these LTSs are efficient enough. Most popular LTSs are those based on plasmonic nanostructures which allow the incident light to concentrate in strongly subwavelength regions inside the PV layers [3]. These structures were, however, heavily criticized for parasitic losses in the metal nanoelements (see e.g. in [4]). Really, high losses in the metal constituents make the light-trapping functionality meaningless. Without an LTS some incident power is absorbed in the bottom electrode, in presence of a plasmonic LTS it can be absorbed inside the latter one, which is not better. Besides of the direct losses of the incident light energy this implies a decrease of the PV conversion efficiency due to the heating of the PV layer [1].A novel regime of perfect absorption in a thin plasmonic layer corresponds to a collective mode of an array of plasmonic nanospheres. In our theoretical study we show that the absorption of the incident light occurs mainly in the semiconductor material hosting plasmonic nanospheres, whereas the absorption in the metal is very small. The regime survives when the uniform host layer is replaced by a practical photovoltaic cell. Trapping the light allows the thickness of the doped semiconductor to be reduced to values for which the degradation under light exposure should be insufficient. The light-trapping regime is compatible with both the metal-backed variant of the photovoltaic cell and its semitransparent variant when both electrodes are preformed of a conductive oxide. Negligible parasitic losses, a variety of design solutions and a reasonable operational band make our perfect plasmonic absorbers promising for photovoltaic applications.

Microgap thermophotovoltaic systems with low emission temperature and high electric output

We theoretically show that a thermophotovoltaic (TPV) system enhanced by a wire metamaterial opens the door to a prospective microgap thermophotovoltaics which will combine high electric output with relatively low temperatures of the emitter. The suggested system comprises an array of parallel metal nanowires grown on top of a photovoltaic semiconductor and standing free in the vacuum gap between the host dielectric layer and the emitter, so that their ends are sufficiently close to the emitting surface. Due to the resonant near-field coupling between this wire medium and the emitter and due to the optimized layered structure of the whole system, the strongly super-Planckian radiative heat flux of resonant nature is engineered.

A non-resonant dielectric metamaterial for the enhancement of thin-film solar cells

Recently, we have suggested a dielectric metamaterial composed of an array of submicron dielectric spheres located on top of an amorphous thin-film solar cell. We have theoretically shown that this metamaterial can decrease the reflection and simultaneously suppress the transmission through the photovoltaic layer because it transforms the incident plane wave into a set of focused light beams. This theoretical concept has been strongly developed and experimentally confirmed in the present paper. Here we consider the metamaterial for oblique angle illumination, redesign the solar cell and present a detailed experimental study of the whole structure. In contrast to our previous theoretical study we show that our omnidirectional light-trapping structure may operate better than the optimized flat coating obtained by plasma-enhanced chemical vapor deposition.

Light Trapping In Thin-Fim Solar Cells: Gain in Spite of Defects

In this work, we report a nanostructure that grants a significant enhancement in optical efficiency to a thin-film solar cell based on amorphous silicon. The fabrication technique is very cheap and the nanostructure can be easily and rapidly prepared on a large area. This is possible by price of numerous mm-sized defects. In the areas of these defects the optical efficiency suffers. However, the enhancement of optical efficiency in the non-defective regions is so significant that the presence of defects still allows the gain granted by our light-trapping structure compared to a standard anti-reflective coating.

Wide-angle light-trapping electrode for photovoltaic cells

In this Letter, we experimentally show that a submicron layer of a transparent conducting oxide that may serve a top electrode of a photovoltaic cell based on amorphous silicon when properly patterned by notches becomes an efficient light-trapping structure. This is so for amorphous silicon thin-film solar cells with properly chosen thicknesses of the active layers (p-i-n structure with optimal thicknesses of intrinsic and doped layers). The nanopatterned layer of transparent conducting oxide reduces both the light reflectance from the photovoltaic cell and transmittance through the photovoltaic layers for normal incidence and for all incidence angles. We explain the physical mechanism of our light-trapping effect, prove that this mechanism is realized in our structure, and show that the nanopatterning is achievable in a rather easy and affordable way that makes our method of solar cell enhancement attractive for industrial adaptations.

Laser deposition of resonant silicon nanoparticles on perovskite for photoluminescence enhancement

Hybrid lead halide perovskite based optoelectronics is a promising area of modern technologies yielding excellent characteristics of light emitting diodes and lasers as well as high efficiencies of photovoltaic devices. However, the efficiency of perovskite based devices hold a potential of further improvement. Here we demonstrate high photoluminescence efficiency of perovskites thin films via deposition of resonant silicon nanoparticles on their surface. The deposited nanoparticles have a number of advances over their plasmonic counterparts, which were applied in previous studies. We show experimentally the increase of photoluminescence of perovskite film with the silicon nanoparticles by 150 % as compared to the film without the nanoparticles. The results are supported by numerical calculations. Our results pave the way to high throughput implementation of low loss resonant nanoparticles in order to create highly effective perovskite based optoelectronic devices.