Terahertz response of patterned epitaxial graphene

We study the interaction between polarized terahertz (THz) radiation and micro-structured large-area graphene in transmission geometry. In order to efficiently couple the radiation into the two-dimensional material, a lateral periodic patterning of a closed graphene sheet by intercalation doping into stripes is chosen. We observe unequal transmittance of the radiation polarized parallel and perpendicular to the stripes. The relative contrast, partly enhanced by Fabry-Perot oscillations reaches 20 %. The effect even increases up to 50 % when removing graphene stripes in analogy to a wire grid polarizer. The polarization dependence is analyzed in a large frequency range from < 80 GHz to 3 THz, including the plasmon-polariton resonance. The results are in excellent agreement with theoretical calculations based on the electronic energy spectrum of graphene and the electrodynamics of the patterned structureThe authors thank J. Jobst for fruitful discussions. The research was performed in the framework of the Sonderforschungsbereich 953 "Synthetic carbon allotropes", funded by Deutsche Forschungsgemeinschaft. We acknowledge support from the EC under Graphene Flagship (contract no. CNECT-ICT-604391)

Terahertz response of patterned epitaxial graphene

We study the interaction between polarized terahertz (THz) radiation and micro-structured large-area graphene in transmission geometry. In order to efficiently couple the radiation into the two-dimensional material, a lateral periodic patterning of a closed graphene sheet by intercalation doping into stripes is chosen. We observe unequal transmittance of the radiation polarized parallel and perpendicular to the stripes. The relative contrast, partly enhanced by Fabry–Perot oscillations reaches 20%. The effect even increases up to 50% when removing graphene stripes in analogy to a wire grid polarizer. The polarization dependence is analyzed in a large frequency range from <80 GHz to 3 THz, including the plasmon–polariton resonance. The results are in excellent agreement with theoretical calculations based on the electronic energy spectrum of graphene and the electrodynamics of the patterned structure

PECVD-ONO: A New Deposited Firing Stable Rear Surface Passivation Layer System for Crystalline Silicon Solar Cells

A novel plasma-enhanced chemical vapour deposited (PECVD) stack layer system consisting of a-SiOx:H, a-SiNx:H, and a-SiOx:H is presented for silicon solar cell rear side passivation. Surface recombination velocities below 60 cm/s (after firing) and below 30 cm/s (after forming gas anneal) were achieved. Solar cell precursors without front and rear metallisation showed implied open-circuit voltages Voc values extracted from quasi-steady-state photoconductance (QSSPC) measurements above 680 mV. Fully finished solar cells with up to 20.0% energy conversion efficiency are presented. A fit of the cell's internal quantum efficiency using software tool PC1D and a comparison to a full-area aluminium-back surface field (Al-BSF) and thermal SiO2 is shown. PECVD-ONO was found to be clearly superior to Al-BSF. A separation of recombination at the metallised and the passivated area at the solar cell's rear is presented using the equations of Fischer and Kray. Nuclear reaction analysis (NRA) has been used to evaluate the hydrogen depth profile of the passivation layer system at different stages

High-efficiency silicon solar cells for low-illumination applications

At Fraunhofer ISE the fabrication of high-efficiency solar cells was extended from a laboratory scale to a small pilot-line production. Primarily, the fabricated cells are used in small high-efficiency modules integrated in prototypes of solar-powered portable electronic devices such as cellular phones, handheld computers etc. Compared to other applications of high-efficiency cells such as solar cars and planes, the illumination densities found in these mainly indoor applications are significantly below 1 sun. Thus, special care was taken to keep the cell efficiency level high even at very low illumination levels. For this reason, particularly the cell border was analyzed and optimized carefully. The excellent cell characteristics achieved at low illumination densities increase the benefit of a solar power supply for such devices by an order of magnitude if compared to standard solar cells. (orig.)Available from: http://www.ise.fhg.de/german/publications/index.html / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman