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8 introduction1.2 physical factors relevant for photoconversionat hybrid interfacesHybrid interfaces belong to the class of excitonic solarcells where the photoconversion is controlled by three mainprocesses:1. Absorption of light and exciton generation,2. charge separation by exciton dissociation at the interface,3. charge transport and collection.All the above physical mechanisms are rooted on theatomic scale of the active layer of the solar cells and theirefficient operation require to control the molecular featuresof the system (such as the position of HOMO and LUMO,the band alignment and so on).The technological overview of the previous section suggeststhat there are many open problems in hybrid systemsthat require a better theoretical investigation. Theseare overview below.The importance of the polymer morphology and organizationat the hybrid interfaces has been discussed in severalrecent studies. For example the low efficiency of theZnO/polymer hybrids has been attributed to the formationof an amorphous area of polymer within the first nanometersfrom the ZnO surface [2, 37]. The polymer disorderis expected to be detrimental for the efficiency of the system.Firstly, it is known that in the amorphous polymerthe lifetime of the carriers is shorter [2] than in the crystallinephase. Secondly, the electronic orbital levels of P3HTand, in turn, the charge transfer efficiency depend on thepolymer crystallinity [38, 2]. Finally, better light absorption[39, 40] and transport properties are found in crystallinepolymer phase.A second fundamental issue of the hybrid interface isrelated to the electronic energy level alignment at the interface,that controls electronic properties such as charge injection,separation and so on. Specifically they depend onthe position of components HOMO and LUMO, which alsodefine their band gap [11]. In particular the LUMO level ofthe acceptor must be located below the LUMO level of the