Influence of inhomogeneous distributions on charge transfer in micro-nano optoelectronic conversion systems

Abstract

The mechanisms of charge transfer are of high importance for the understanding of photophysical processes in the complex photo-electron conversion systems, i.e., natural photosynthesis systems and dye-sensitized photovoltaics. Since these physical mechanisms are usually deep hidden by the subtle interactions between the subjects in study and the surrounding environments, drawing a general profile of the experimentally observed charge transfer kinetics from the universality point of view is of benefit and necessary. In this way, according to our previous works, these efforts on the aspect of charge transfer involved with both theoretical models and time-resolved experiments on the dynamical and static inhomogeneous distribution in the complex photo-electron conversion systems are summarized in this review. After a short critical survey of classic electron transfer theories, for example, the early Marcus expression, where there are two adjustable parameters, that is the driving force and reorganization energy, we focus on the recent efforts concerning the roles of inhomogeneous distributions of the static interaction (electronic coupling) and dynamical structure motions (static and dynamical inhomogeneous distribution) in these complex photo-electron conversion systems, such as protein dynamics in natural photosynthesis systems and initial electron injection in dye-sensitized systems. The details of the static and dynamical inhomogeneous distribution models are introduced at first. They are divided by the interaction types between the reactants/products and the surrounding environment in the complex photo-electron conversion systems. For the dynamical inhomogeneous distribution model in the reaction center of natural photosynthesis systems, it highlights the complex solvent environment, such as the protein environment of the reaction center. While for the static inhomogeneous distribution model in the dye-sensitized and quantum dot-sensitized solar cell systems, it considers that there are many sub-energy states, and assumes that the energy distribution of these sub-energy states meets a static Gaussian function. Thus, the change of driving force can be represented by the local shift in the energies of the oxide acceptor states relative to excited state of the dyes or quantum dots. In combination with theoretical models, this review shows that ultrafast spectroscopy as a powerful tool will continue to play an important role in the exploration of the hidden photophysical mechanisms in modern photo-electron conversion systems. Up to now, although there have been significant advances in the research of charge transfer mechanism in the complex photo-electron conversion systems, there are still many physical phenomena not fully understood, which are waiting for further investigation by ultrafast spectroscopic techniques with higher time-space resolution capabilities.