Electron Transfer at Quantum Dot–Metal Oxide Interfaces for Solar Energy Conversion

Abstract

Electron transfer at a donor–acceptor quantum dot–metal oxide interface is a process fundamentally relevant to solar energy conversion architectures as, e.g., sensitized solar cells and solar fuels schemes. As kinetic competition at these technologically relevant interfaces largely determines device performance, this Review surveys several aspects linking electron transfer dynamics and device efficiency; this correlation is done for systems aiming for efficiencies up to and above the ∼33% efficiency limit set by Shockley and Queisser for single gap devices. Furthermore, we critically comment on common pitfalls associated with the interpretation of kinetic data obtained from current methodologies and experimental approaches, and finally, we highlight works that, to our judgment, have contributed to a better understanding of the fundamentals governing electron transfer at quantum dot–metal oxide interfaces.

Investigation of Interface Characteristics and Physisorption Mechanism in Quantum Dots/TiO2 Composite for Efficient and Sustainable Photoinduced Interfacial Electron Transfer

“…In general, the degree of electronic coupling between TiO 2 and the QDs loaded on its surface and the PET efficiency at the QD/TiO 2 interface are related to the intricate surface treatment and linking strategies employed to achieve efficient QD adsorption on the TiO 2 surface. − Although various adsorption techniques, such as linker-assisted deposition ( ex / in situ ligand exchange and in situ growth), − self-assembled monolayer (SAM) formation, , photodeposition, successive ionic layer adsorption and reaction (SILAR), , and chemical bath deposition, − have been used for docking QDs onto the TiO 2 surface, these methods are not suitable for practical applications owing to their complexity and the limited QD-loading capacity of the TiO 2 surface. In this regard, direct physical adsorption entailing the simple blending of dispersed QDs and heterogeneous metal-oxide nanoparticles is considered an efficient and practical method owing to its simplicity, provided that satisfactory loading capacity and adsorption stability on the semiconductor surface are guaranteed. ,, Although the adsorption mechanism of this direct loading method has not been fully elucidated, it has been extensively utilized to fabricate quantum-dot-sensitized solar cells because it delivers comparable or superior adsorption capacities/interfacial PET efficiencies compared to those of the typical linking method entailing the use of 3-mercaptopropionic acid while allowing for straightforward manipulation without requiring surface ligand linkage. ,, While some studies on the adsorption mechanism of QDs on TiO 2 surfaces have been published, there is currently no generally accepted explanation for the direct adsorption of QDs on TiO 2 surfaces. , …”

How Effective Are Sub-Bandgap States in AgInS2 Quantum Dots for Electron Transfer?

“…The interfacial electron transfer involving semiconductor quantum dots is pivotal to the application of these nanoparticles in photocatalysis , and photovoltaic devices. − The main bottleneck to this critical step (electron transfer) is the competing recombination and trapping processes of charge carriers . For this reason, charge separation to boost the lifetime of charge carriers is a crucial step in the operation of quantum dot-based processes/devices .…”

Ultrafast and Nanoscale Energy Transduction Mechanisms and Coupled Thermal Transport across Interfaces

“…At interfaces and surfaces in nanomaterials, these intertwined mechanisms are the foundation of the modern technologies that are continuing to provide transformational benefits in computing, communication, health care, clean energy, power recycling, sensing, and manufacturing, to name a few. For example, transistors rely on the interaction of field with carriers across metal/oxide/active region boundaries, − catalysis can be greatly enhanced through non-equilibrium charge injection across interfaces before thermal equilibration with phonons, − and the ability of photoexcited charges to efficiently couple across a semiconductor/metal interface dictates the efficiency of solar energy harvesting devices. − In these applications, the interaction and transport among the various carriers across and around the interface between two materials give rise to increased energy density, which can result in deleterious temperature rises that can impact the efficiency of the devices. − Specifically, it is well known that the resulting thermal boundary resistances (TBRs) that occur at interfaces of two different materials or phases of matter are the limiting factor that dictate, for example, the scalability of transistors in CMOS architectures that drives the semiconductor industry’s capability to keep pace with Moore’s law; − the ability of wide- and ultrawide-bandgap-based power devices from achieving their intrinsic material potentials in RF power converters for applications ranging from military radar systems to wireless communication for 6G and beyond; and the efficiency of photothermal therapeutics to maintain localized and controlled temperature rise to target selective treatment of cancerous cells while ensuring the healthy tissues are unperturbed …”