Electron injection efficiency in dye-sensitized solar cells

Abstract

Electron injection processes in dye-sensitized solar cells (DSCs), which involve electron transfer from an excited dye to a semiconductor nanoparticle, have been discussed in many previously reported studies. In this review we discuss the working principles and primary processes of DSCs, as well as these processes’ influence on basic properties of solar cells such as open-circuit voltage, short-circuit current, and incident photon-to-current conversion efficiency (IPCE). We focus our attention on the electron injection process, and we introduce methods to determine electron injection efficiency (Φinj) using time-resolved fluorescence and absorption spectroscopy techniques. We present difficulties associated with obtaining Φinj by means of such techniques, and we propose nanosecond time-resolved transient absorption spectroscopy as a reliable method. Then, Φinj values obtained are summarized. Factors limiting Φinj are discussed from the perspective of free energy changes for electron injection, the molecular structure of sensitizer dyes on the surface, and the presence of fast charge recombination pathways.