Engineering FRET-Based Solar Cells: Manipulation of Energy and Electron Transfer Processes in a Light Harvesting Assembly

Abstract

From the prevalent interest in the advancement of renewable energy sources, dye-sensitized solar cells (DSSCs) have emerged as one of the front running prospects due mainly to a constructive balance between cost and efficiency. In this chapter, we will review our works on the utility of using Forster resonance energy transfer (FRET) in the light harvesting dynamics of zinc oxide (ZnO)-based nanomaterials, which has recently shown promise for significant improvement in various aspects of photoelectrochemical cells. Firstly, we have used ZnO nanoparticles (NPs) and Oxazine 1 as model donor and acceptor, respectively, to investigate the key ultrafast process of FRET in the NP–dye system. The consequence of the energy transfer on the performance of a model ZnO NP-based DSSC has also been explored by using well-known Ruthenium-based sensitizers N719 attached to ZnO NPs offering as an intrinsic co-sensitizer. By using a picosecond-resolved FRET technique, we have also demonstrated the role of the gold layer in promoting photoinduced charge transfer from ZnO–Au nanocomposite to a model contaminant methylene blue (MB). Due to the formation of the Schottky barrier at the ZnO–Au interface and the higher optical absorptions of the ZnO–Au photoelectrodes arising from the surface plasmon absorption of the Au NPs, enhanced power-conversion efficiency was achieved compared to bare ZnO-based DSSCs. Finally, potential co-sensitization of extrinsic sensitizer CdTe quantum dots (QDs) in ZnO nanorod (NR)-based DSSCs has been established where we have shown two major pathways by which CdTe QDs may contribute to the net photocurrent in a DSSC: (1) a direct injection of charge carriers from QDs to ZnO semiconductor via photoinduced electron transfer (PET) and (2) an indirect excitation of the sensitizing dye N719 molecules by funneling harvested light via FRET. Based on these advantages, the short-circuit current density and the photoconductivity of the QD-assembled DSSCs with distinct architectures are found to be much higher than DSSCs fabricated with N719 sensitizer only. As demonstrated, the multipath enhancement offered in this device architecture results in an increased and extended photo-response with respect to the individual materials employed. Further engineering of suitable donor acceptor pairs and optimization of charge separation in conjugated molecular blends has the potential to become a continuing avenue toward enhancing hybrid DSSC efficiencies.