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Results on photonic structures

From Fraunhofer ISE:

In silicon solar cells, photons with energies lower than the fixed bandgap of 1.12 eV are transmitted through the semiconductor material and do not contribute to current generation. The solar cell concept shown here aims to overcome this general limitation. This can be achieved using an upconverting material below the solar cell, which transforms two or more low-energy photons into one high-energy photon, which can be utilized in the solar cell. Available efficient upconverters like NaYF4:Er, however, typically only work efficiently over a narrow wavelength range. This narrow spectral range can be enlarged using a second luminescent material, which absorbs over a wider spectral range and emits in the absorption range of the upconverter, a concept known as spectral concentration. Thus, photons in different wavelength regimes are utilized most efficiently in different regions within the system. In order to distribute the photons according to their wavelength, photonic structures are required.


Fig. 1.: Upconverter filter produced with 20 layers of amorphous silicon carbide deposited on a glass substrate. The red line represents the simulated characteristics and the blue line shows the measurement. The thicknesses of the layers have been determined by spectroscopic ellipsometry and were taken as a base for the simulations.

Figure 2 shows the comparison of measured and simulated reflection characteristics of the upconverter filter deposited on a glass substrate. The peak lies at the intended 1000 nm and above this wavelength, the reflection decreases to very low values:


Fig. 2.: Comparison between the simulation and measurement of the spatial concentration filter. The structure consists in total of 35 layers of amorphous silicon carbide deposited on a glass substrate.

Figure 3 shows an SEM micrograph of the same filter:

UC_Filter REM_klein

Fig. 3: SEM micrograph of the polished cross-section of the upconverter filter with the characteristics shown in figure 4. The micrograph shows alternating a-SixC1-x-layers of two different configurations with different thicknesses deposited on a glass substrate.


Furthermore, the spatial concentration filter needed above the fluorescent concentrator in the regions where no upconverter is present has been produced. The structure was realized based on the same material system, as stacked layers of silicon carbides with two different configurations.

It has been shown that the photonic structures needed to produce an efficient solar cell system including upconverters and fluorescent concentrators, can be produced based on stacked layers of amorphous silicon carbides of different configurations. It has been shown that the simulations and measurements of these one-dimensional photonic structures show very good agreement.



Publications on photonic structures


One-Dimensional SiC Photonic Structures to Enhance the Efficiency of systems with silicon solar cells and upconverters (EUPVSEC 2011)

Photonic Structures for a Solar Cell-Upconversion-System (FuturePV)

Enhancement of Upconversion Efficiency by Manipulation of Photonic Structures: A Review (PVSAT-7)



Exploiting Photonic Structures to improve the Efficiency of Upconversion, utilizing both Field Enhancement and modified LDOS (EUPVSEC 2012)


The Nanospec Project is funded by the European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement no. [246200].

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