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6 introductionprocesses that need to be eliminated to ensure stability [22,26].A possible and widely studied alternative to the organicsolar cells are the hybrid organic-inorganic systems, composedby an organic conductive polymer and a cheap andenvironmental friendly inorganic semiconductor, such as ametal oxide. These systems are of great interest since theycombine the peculiar properties of the two kinds of materialsinvolved at a relatively low cost of production. Inparticular, they allow to join the tailorable properties andthe flexibility of the organic polymers with the thermal andmechanical stability and the good transport properties ofthe inorganic materials [27].In hybrid solar cells the role of the acceptor is played bythe inorganic material, such as TiO 2 or ZnO, while the conductivepolymer (tipically the P3HT) has the role of electrondonor. Such systems are promising for their technologicalimpact though, until now, the highest achieved efficiencyfor a ZnO/P3HT binary system is as low as 2% [28](see Figure 1.4). This result is not comparable with that obtainedby fully organic devices and a clear motivation forthis poor behavior is still missing.Figure 1.4.: Efficiency of hybrid solar cells composed by P3HT andTiO 2 or ZnO.However, not all hybrid technologies have poor efficiencies.The most competitive hybrid systems are represented