ABSTRACT
In this chapter, the separation of the excitation into distinct carriers is analyzed, with particular emphasis on those devices composed of different nanostructured phases that realize the charge separation by energetic gradients close to the generation point, such as dye-sensitized solar cells and organic bulk heterojunction cells. In particular, the use of separate phases for electron and hole transport imposes constraints on the open-circuit voltage value because the Fermi level is limited by the density of states of the transport materials. The operation of a solar cell can be analyzed in terms of a sequential set of processes, which eventually cause the conversion of the free energy of the incoming photons into a voltage and current extracted at the outer contacts of the device. Authors discuss in turn the processes of light absorption and charge separation. Charge separation means that initially formed electron-hole pairs after photogeneration dissociate to form two separate unbound charge carriers of opposite polarity.
