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The mobility of the metamorphic InGaAs structure is low, down to 500 cm2/V.s, since it possibly contains threading dislocations of high density and the latter causes relatively poor material quality. High values over 2000 cm2/ V.s for Hall mobility exhibits the lattice matched to GaAs substrate InGaAsN sample. These values are about the theoretical limit predicted by Fahy and O'Reilly (Fahy and O'Reilly, 2004) and among the highest reported

Dilute nitride GaAsN and InGaAsN epitaxial layers have been prepared by lowtemperature LPE using polycrystalline GaN as a source for nitrogen. The GaAsN layers, 0.8- 1.5 μm thick, with 0.15-0.6 at. % N content in the solid have been grown from different initial epitaxy temperature varied in the range 650-550 °C. The lowering the epitaxy temperatures favors nitrogen incorporation in the layers. The Hall measurements reveal sharply increase of free carrier concentrations about one order of magnitude and decrease of Hall mobility

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**5** 

Yunfei Zhou,

*Germany* 

Michael Eck and Michael Krüger

**Organic-Inorganic Hybrid Solar Cells:** 

*University of Freiburg/Freiburg Materials Research Centre* 

**State of the Art, Challenges and Perspectives** 

Novel photovoltaic (PV) technologies are currently investigated and evaluated as approaches to contribute to a more environmental friendly energy supply in many countries. One of the driving forces are the aims to reduce the emission of green house gases and the dependency on importing fossil energy resources from political unstable countries. Additionally the wish to replace nuclear power by greener and less threatening technologies will enhance the development of regenerative energy supply in many countries especially after the recent nuclear catastrophe at Fukushima nuclear power plant in Japan in March 2011. This will include the more rapid implementation of existing mature PV technologies but also the development and improvement of novel PV approaches such as organic PV (OPV) and dye-sensitized solar cells (DSSCs) together with new efficient strategies for energy storage and distribution to make electric power, deriving from PVs, available

The so-called 1st generation of solar cells based on e.g. bulk crystalline and polycrystalline silicon is still dominating the PV market. However, so-called 2nd generation solar cells mainly consisting out of thin film solar cells based on CdTe, Copper Indium Gallium Selenide (CIGS), and amorphous silicon gained distribution of ca. 25% in market share today worldwide. It is expected that this number will increase significantly within the next years. While for the 1st and 2nd generation solar cells commercial solar panels are available with decent power conversion efficiencies (PCEs) and lifetimes, the emerging 3rd generation solar cells such as OPV and DSSCs technologies are still in the development phase. Some commercially available products have recently entered the market such as e.g. solar bags representing niche products, which are so far not suitable for competing with traditional large scale applications of solar panels of the 1st and 2nd generations. In traditional solar panels the differences between best solar cell and average solar cell efficiencies are much smaller than for the emerging solar cell technologies with the consequence that modules of 3rd generation solar cells still suffer from too low performance. In Table 1 the best cell and module efficiencies of different PV technologies are compared. It has to be mentioned that especially for the emerging new PV technologies the average efficiencies are significantly

**1. Introduction** 

whenever and wherever it is needed.

lower than the results of the best cells.

