ABSTRACT
This chapter analyses the separation of the excitation into distinct carriers, with particular emphasis on devices composed of different nanostructured phases that realize the charge separation by energetic gradients close to generation point, such as dye-sensitized solar cells and organic bulk heterojunction cells. It discusses the processes of light absorption and charge separation. Effective local charge separation is an essential feature to avoid immediate geminate recombination of individually photogenerated electron–hole pairs in low permittivity absorbers and/or at low temperatures. Specific mechanisms of charge separation may differ broadly depending on type of absorber and its relative permittivity. Many types of solar cells rely on a homogeneous semiconductor absorber layer that realizes both the functions of charge separation and carrier transport for their collection at the selective contacts. However, several types of nanostructured solar cells that use organic materials as absorbers establish a combination of materials to realize effective charge separation and subsequently, the transport of carriers occurs in separated phases.
