This is a nice review paper that summarizes the present status of organic solar cells, dye-sensitized solar cells, quantum dot solar cells, and inorganic polycrystalline solar cells.
Materials interface engineering for solution-processed photovoltaics
Michael Graetzel, René A. J. Janssen, David B. Mitzi & Edward H. Sargent
Nature 488,304–312(16 August 2012)
There’s free acces (for the moment):