Photoluminescence is light emission from any form of matter after the absorption of photons. It is one of many forms of luminescence and is initiated by photoexcitation, hence the prefix photo-. Following excitation, various relaxation processes typically occur in which other photons are re-radiated. Time periods between absorption and emission may vary: ranging from short femtosecond-regime for emission involving free-carrier plasma in inorganic semiconductors up to milliseconds for phosphoresence processes in molecular systems; and under special circumstances delay of emission may even span to minutes or hours.
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.
In chemistry, chromism is a process that induces a change, often reversible, in the colors of compounds. In most cases, chromism is based on a change in the electron states of molecules, especially the π- or d-electron state, so this phenomenon is induced by various external stimuli which can alter the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date. It is usually synonymous with chromotropism, the (reversible) change in color of a substance due to the physical and chemical properties of its ambient surrounding medium, such as temperature and pressure, light, solvent, and presence of ions and electrons.
Artificial photosynthesis is a chemical process that biomimics the natural process of photosynthesis. The term artificial photosynthesis is used loosely, refer to any scheme for capturing and storing energy from sunlight by producing a fuel, specifically a solar fuel. An advantage of artificial photosynthesis is that the solar energy can be immediately converted and stored. By contrast, using photovoltaic cells, sunlight is converted into electricity and then converted again into chemical energy for storage, with some necessary losses of energy associated with the second conversion. The byproducts of these reactions are environmentally friendly. Artificially photosynthesized fuel would be a carbon-neutral source of energy, which could be used for transportation or homes. The economics of artificial photosynthesis are not competitive.
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.
A solar cell or photovoltaic cell is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect. It is a form of photoelectric cell, a device whose electrical characteristics vary when it is exposed to light. Individual solar cell devices are often the electrical building blocks of photovoltaic modules, known colloquially as "solar panels". Almost all commercial PV cells consist of crystalline silicon, with a market share of 95%. Cadmium telluride thin-film solar cells account for the remainder. The common single-junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.
Photosensitizers are light absorbers that alter the course of a photochemical reaction. They usually are catalysts. They can function by many mechanisms, sometimes they donate an electron to the substrate, sometimes they abstract a hydrogen atom from the substrate. At the end of this process, the photosensitizer returns to its ground state, where it remains chemically intact, poised to absorb more light. One branch of chemistry which frequently utilizes photosensitizers is polymer chemistry, using photosensitizers in reactions such as photopolymerization, photocrosslinking, and photodegradation. Photosensitizers are also used to generate prolonged excited electronic states in organic molecules with uses in photocatalysis, photon upconversion and photodynamic therapy. Generally, photosensitizers absorb electromagnetic radiation consisting of infrared radiation, visible light radiation, and ultraviolet radiation and transfer absorbed energy into neighboring molecules. This absorption of light is made possible by photosensitizers' large de-localized π-systems, which lowers the energy of HOMO and LUMO orbitals to promote photoexcitation. While many photosensitizers are organic or organometallic compounds, there are also examples of using semiconductor quantum dots as photosensitizers.
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 captivating 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 adjustable 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.
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.
Thin-film solar cells are made by depositing one or more thin layers of photovoltaic material onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers (nm) to a few microns (µm) thick–much thinner than the wafers used in conventional crystalline silicon (c-Si) based solar cells, which can be up to 200 µm thick. Thin-film solar cells are commercially used in several technologies, including cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon.
Arthur J. Nozik is a researcher at the National Renewable Energy Lab (NREL). He is also a professor at the University of Colorado, which is located in Boulder. He researches semiconductor quantum dots at the National Renewable Energy Laboratory, and is a chemistry professor at the University of Colorado. He also does research for the advancement of solar energy, for which he won the Intergovernmental Renewable Energy Organization (IREO) Award for Science and Technology in 2009.
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 which 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 a part of the substrate.
Photoelectrochemistry is a subfield of study within physical chemistry concerned with the interaction of light with electrochemical systems. It is an active domain of investigation. One of the pioneers of this field of electrochemistry was the German electrochemist Heinz Gerischer. The interest in this domain is high in the context of development of renewable energy conversion and storage technology.
Photon upconversion (UC) is a process in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength. It is an anti-Stokes type emission. An example is the conversion of infrared light to visible light. Upconversion can take place in both organic and inorganic materials, through a number of different mechanisms. Organic molecules that can achieve photon upconversion through triplet-triplet annihilation are typically polycyclic aromatic hydrocarbons (PAHs). Inorganic materials capable of photon upconversion often contain ions of d-block or f-block elements. Examples of these ions are Ln3+, Ti2+, Ni2+, Mo3+, Re4+, Os4+, and so on.
Solar energy conversion describes technologies devoted to the transformation of solar energy to other (useful) forms of energy, including electricity, fuel, and heat. It covers light-harvesting technologies including traditional semiconductor photovoltaic devices (PVs), emerging photovoltaics, solar fuel generation via electrolysis, artificial photosynthesis, and related forms of photocatalysis directed at the generation of energy rich molecules.
Villy Sundström is a Swedish physical chemist known for his work in ultrafast science and molecular photochemistry using time-resolved laser and X-ray spectroscopy techniques.
Krishnan Rajeshwar is a chemist, researcher and academic. He is a Distinguished University Professor and Founding Director of the Center for Renewable Energy Science & Technology at The University of Texas at Arlington.
