Dynamics and Mechanisms of Interfacial Photoinduced Electron Transfer Processes of Third Generation Photovoltaics and Photocatalysis

Abstract

Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo-and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a Ru II (terpyridyl-PO 3 )(NCS) 3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO 2 . The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the μs time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor β = 0.16 Å -1 observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO 2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface.

Charge transfer versus molecular conductance: molecular orbital symmetry turns quantum interference rules upside down

“…In Fig. 9(b), the computed (J ET eff ) 2 for electron transfer from the initially delocalized state to the LUMO + 2 PDI is compared to the experimentally determined k ET . Although (J ET eff ) 2 reects the same trend as the experimental k ET , it overestimates the difference in k ET within 2mm, 2mp, and 2pp.…”

“…Charge transfer in organic molecules is a process that is of fundamental and practical importance in several areas of science and technology. Important technological innovations, such as organic solar cells, 1,2 water splitting devices, 3 or single molecule electronics, [4][5][6][7][8][9] heavily rely on the control of intramolecular charge transfer reactions. A detailed understanding of these reactions along complex molecules is therefore of prime importance.…”

Energy Band Gap Investigation of Biomaterials: A Comprehensive Material Approach for Biocompatibility of Medical Electronic Devices

“…Such systems are modeled as donor-acceptor heterojunctions. Depending at the energy levels of the HOMO and LUMO of the two materials, the electrons and holes become separated; electrons fall into lower energy states and holes rise to higher energies [34,35]. Such charge separation decreases the radiative recombination.…”

Nanozymes Regulate Redox Homeostasis in ROS-Related Inflammation

“…For example, it was found that OH˙ is generated during the photolysis of ozone. Identifying the processes of the formation of ROS may help utilize ROS by avoiding its ill effects ( Bauer et al, 2011 ).…”