Nanocomposite solar cells: the requirement and challenge of kinetic charge separation

Nanocrystalline solar cells promise significant advantages with respect to cost-efficient mass production, since they do not require imprinted chemical potential gradients for charge separation (e.g., electrical fields generated by p, n doping, which should last for one to three decades). They, however, require kinetic charge separation and chemical electronic mechanisms, which rectify photocurrents for energy conversion. Such mechanisms are presently not well understood, since the existing nanosolar cells (dye and polymer solar cells) have evolved largely empirically. It is shown in this paper that function and properties of kinetically determined solar cells can be derived from irreversible thermodynamic principles considering minimum entropy production (or the principle of least action) and involve solid-state electrochemical processes. Based on this model, presently studied nanosolar cells and also the primary photosynthetic mechanism are analyzed to identify the most significant physical-chemical factors involved.