Redox is a type of chemical reaction in which the oxidation states of substrate change.
A "photoelectrochemical cell" is one of two distinct classes of device. The first produces electrical energy similarly to a dye-sensitized photovoltaic cell, which meets the standard definition of a photovoltaic cell. The second is a photoelectrolytic cell, that is, a device which uses light incident on a photosensitizer, semiconductor, or aqueous metal immersed in an electrolytic solution to directly cause a chemical reaction, for example to produce hydrogen via the electrolysis of water.
Artificial photosynthesis is a chemical process that biomimics the natural process of photosynthesis to convert sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term artificial photosynthesis is commonly used to refer to any scheme for capturing and storing the energy from sunlight in the chemical bonds of a fuel. Photocatalytic water splitting converts water into hydrogen and oxygen and is a major research topic of artificial photosynthesis. Light-driven carbon dioxide reduction is another process studied that replicates natural carbon fixation.
In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalyzed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity (PCA) depends on the ability of the catalyst to create electron–hole pairs, which generate free radicals (e.g. hydroxyl radicals: •OH) able to undergo secondary reactions. Its practical application was made possible by the discovery of water electrolysis by means of titanium dioxide (TiO2).
A dye-sensitized solar cell is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system. The modern version of a dye solar cell, also known as the Grätzel cell, was originally co-invented in 1988 by Brian O'Regan and Michael Grätzel at UC Berkeley and this work was later developed by the aforementioned scientists at the École Polytechnique Fédérale de Lausanne (EPFL) until the publication of the first high efficiency DSSC in 1991. Michael Grätzel has been awarded the 2010 Millennium Technology Prize for this invention.
The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical and chemical phenomenon.
Hybrid solar cells combine advantages of both organic and inorganic semiconductors. Hybrid photovoltaics have organic materials that consist of conjugated polymers that absorb light as the donor and transport holes. Inorganic materials in hybrid cells are used as the acceptor and electron transporter in the structure. The hybrid photovoltaic devices have a potential for not only low-cost by roll-to-roll processing but also for scalable solar power conversion.
A quantum dot solar cell (QDSC) is a solar cell design that uses quantum dots as the absorbing photovoltaic material. It attempts to replace bulk materials such as silicon, copper indium gallium selenide (CIGS) or cadmium telluride (CdTe). Quantum dots have bandgaps that are tunable across a wide range of energy levels by changing their size. In bulk materials, the bandgap is fixed by the choice of material(s). This property makes quantum dots attractive for multi-junction solar cells, where a variety of materials are used to improve efficiency by harvesting multiple portions of the solar spectrum.
Photoinduced electron transfer (PET) is an excited state electron transfer process by which an excited electron is transferred from donor to acceptor. Due to PET a charge separation is generated, i.e., redox reaction takes place in excited state.
Heinz Gerischer was a German scientist. He was the thesis advisor of future Nobel laureate Gerhard Ertl.
Organic photovoltaic devices (OPVs) are fabricated from thin films of organic semiconductors, such as polymers and small-molecule compounds, and are typically on the order of 100 nm thick. Because polymer based OPVs can be made using a coating process such as spin coating or inkjet printing, they are an attractive option for inexpensively covering large areas as well as flexible plastic surfaces. A promising low cost alternative to conventional solar cells made of crystalline silicon, there is a large amount of research being dedicated throughout industry and academia towards developing OPVs and increasing their power conversion efficiency.
Photocatalytic water splitting is an artificial photosynthesis process with photocatalysis used for the dissociation of water (H2O) into hydrogen (H
2) and oxygen (O
2), using light. Theoretically, only light energy (photons), water, and a catalyst are needed. This topic is the focus of much research, but as of 2017 no technology has been commercialized. The process remains commercialy unfavorable due to a need for high energy input for water splitting.
Photoelectrochemical processes are processes in photoelectrochemistry; they usually involve transforming light into other forms of energy. These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, and photochromism.
Nanocrystal solar cells are solar cells based on a substrate with a coating of nanocrystals. The nanocrystals are typically based on silicon, CdTe or CIGS and the substrates are generally silicon or various organic conductors. Quantum dot solar cells are a variant of this approach, but take advantage of quantum mechanical effects to extract further performance. Dye-sensitized solar cells are another related approach, but in this case the nano-structuring is part of the substrate.
Photoelectrochemical reduction of carbon dioxide, also known as photoelectrolysis of carbon dioxide, is a chemical process whereby carbon dioxide is reduced to carbon monoxide or hydrocarbons by the energy of incident light. This process requires catalysts, most of which are semiconducting materials. The feasibility of this chemical reaction was first theorised by Giacomo Luigi Ciamician, an Italian photochemist. Already in 1912 he stated that "[b]y using suitable catalyzers, it should be possible to transform the mixture of water and carbon dioxide into oxygen and methane, or to cause other endo-energetic processes."
A solar fuel is a synthetic chemical fuel produced from solar energy. Solar fuels can be produced through photochemical, photobiological, thermochemical, and electrochemical reactions. Light is used as an energy source, with solar energy being transduced to chemical energy, typically by reducing protons to hydrogen, or carbon dioxide to organic compounds.
Adam Heller is an Israeli American scientist and engineer. He is Chief Science Officer of SynAgile Corp. of Wilson, Wyoming, consults to Abbott Diabetes Care of Alameda, California, and is Ernest Cockrell Sr. Chair Emeritus of Engineering at The University of Texas at Austin. His 1973 paper with James J. Auborn established the feasibility of high energy density, high-voltage, non-rechargeable lithium batteries. Their 3.6-volt lithium thionyl chloride and 3.7-volt lithium sulfuryl chloride batteries remain in use in applications requiring very high energy density and a shelf life of 20 years or more.
Biological photovoltaics (BPV) is an energy-generating technology which uses oxygenic photoautotrophic organisms, or fractions thereof, to harvest light energy and produce electrical power. Biological photovoltaic devices are a type of biological electrochemical system, or microbial fuel cell, and are sometimes also called photo-microbial fuel cells or “living solar cells”. In a biological photovoltaic system, electrons generated by photolysis of water are transferred to an anode. A relatively high-potential reaction takes place at the cathode, and the resulting potential difference drives current through an external circuit to do useful work. It is hoped that using a living organism as the light harvesting material, will make biological photovoltaics a cost-effective alternative to synthetic light-energy-transduction technologies such as silicon-based photovoltaics.
Quantum photoelectrochemistry is the investigation of the quantum mechanical nature of photoelectrochemistry, the subfield of study within physical chemistry concerned with the interaction of light with electrochemical systems, typically through the application of quantum chemical calculations. Quantum photoelectrochemistry provides an expansion of quantum electrochemistry to processes involving also the interaction with light (photons). It therefore also includes essential elements of photochemistry. Key aspects of quantum photoelectrochemistry are calculations of optical excitations, photoinduced electron and energy transfer processes, excited state evolution, as well as interfacial charge separation and charge transport in nanoscale energy conversion systems.
In semiconductor physics, the flat band potential of a semiconductor defines the potential at which there is no depletion layer at the junction between a semiconductor and an electrolyte or p-n-junction. This is a consequence of the condition that the redox Fermi level of the electrolyte must be equal to the Fermi level of the semiconductor and therefore preventing any band bending of the conduction and valence band. An application of the flat band potential can be found in the determining the width of the space charge region in a semiconductor-electrolyte junction. Furthermore, it is used in the Mott-Schottky equation to determine the capacitance of the semiconductor-electrolyte junction and plays a role in the photocurrent of a photoelectrochemical cell. The value of the flat band potential depends on many factors, such as the material, pH and crystal structure of the material
Figure 1(a) band diagram of n-type semiconductor/liquid junction
Figure 1(b) band diagram of p-type semiconductor/liquid junction
