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Among these, dye sensitized solar cells
\cite{Gratzelnature, Soga}
(DSCs, also called Gr\"atzel cells) are the most promising one 
\cite{Hagfeldt}.

As a principle, in the all types of solar cells, three successive steps 
must be occur for solar to electrical power conversion
\cite{Wurfel}: 
charge (electron-hole: $e\!-\!h$) generation,
spatially $e\!-\!h$ separation, and the charges transport.

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