I-III-VI2 semiconductors are solid semiconducting materials that contain three or more chemical elements belonging to groups I, III and VI (IUPAC groups 1/11, 13 and 16) of the periodic table. They usually involve two metals and one chalcogen. Some of these materials have a direct bandgap, Eg, of approximately 1.5 eV, which makes them efficient absorbers of sunlight and thus potential solar cell materials. A fourth element is often added to a I-III-VI2 material to tune the bandgap for maximum solar cell efficiency. A representative example is copper indium gallium selenide (CuInxGa(1–x)Se2, Eg = 1.7–1.0 eV for x = 0–1 [1] ), which is used in copper indium gallium selenide solar cells.
CuGaO2 exists in two main polymorphs, α and β. The α form has the delafossite crystal structure and can be prepared by reacting Cu2O with Ga2O3 at high temperatures. The β form has a wurtzite-like crystal structure (space group Pna21); it is metastable, but exhibits a long-term stability at temperatures below 300 °C. [3] It can be obtained by an ion exchange of Na+ ions in a β-NaGaO2 precursor with Cu+ ions in CuCl under vacuum, to avoid the oxidation of Cu+ to Cu2+. [2]
Unlike most I-III-VI2 oxides, which are transparent, electrically insulating solids with a bandgap above 2 eV, β-CuGaO2 has a direct bandgap of 1.47 eV, which is favorable for solar cell applications. In contrast, β-AgGaO2 and β-AgAlO2 have an indirect bandgap. Undoped β-CuGaO2 is a p-type semiconductor. [2]
Similarly to CuGaO2, α-AgGaO2 and α-AgAlO2 have the delafossite crystal structure while the structure of the corresponding β phases is similar to wurtzite (space group Pna2a). β-AgGaO2 is metastable and can be synthesized by ion exchange with a β-NaGaO2 precursor. The bandgaps of β-AgGaO2 and β-AgAlO2 (2.2 and 2.8 eV respectively) are indirect; they fall into the visible range and can be tuned by alloying with ZnO. For this reason, both materials are hardly suitable for solar cells, but have potential applications in photocatalysis. [2]
Contrary to LiGaO2, AgGaO2 can not be alloyed with ZnO by heating their mixture because of the Ag+ reduction to metallic silver; therefore, magnetron sputtering of AgGaO2 and ZnO targets is used instead. [2]
Pure single crystals of β-LiGaO2 with a length of several inches can be grown by the Czochralski method. Their cleaved surfaces have lattice constants that match those of ZnO and GaN and are therefore suitable for epitaxial growth of thin films of those materials. β-LiGaO2 is a potential nonlinear optics material, but its direct bandgap of 5.6 eV is too wide for visible light applications. It can be reduced down to 3.2 eV by alloying β-LiGaO2 with ZnO. The bandgap tuning is discontinuous because ZnO and β-LiGaO2 do not mix but form a Zn2LiGaO4 phase when their ratio is between ca. 0.2 and 1. [2]
LiGaTe2 crystals with a size up to 5 mm can be grown in three steps. First, Li, Ga, and Te elements are fused in an evacuated quartz ampoule at 1250 K for 24 hours. At this stage Li reacts with the ampoule walls, releasing heat, and is partly consumed. In the second stage, the melt is homogenized in a sealed quartz ampoule, which is coated inside with pyrolytic carbon to reduce Li reactivity. The homogenization temperature is selected ca. 50 K above the melting point of LiGaTe2. The crystals are then grown from the homogenized melt by the Bridgman–Stockbarger technique in a two-zone furnace. The temperature at the start of crystallization is a few degrees below the LiGaTe2 melting point. The ampoule is moved the cold zone at a rate of 2.5 mm/day for 20 days. [4]
Formula | a (Å) | b (Å) | c (Å) | Space group | Density (g/cm3) | Melting point (K) | Bandgap (eV) |
---|---|---|---|---|---|---|---|
α-LiGaO2 [6] | 2.92 | 2.92 | 14.45 | R3m | 5.07 | m | 5.6d |
β-LiGaO2 [7] | 5.406 | 6.379 | 5.013 | Pna21 | 4.18 | m | 5.6d |
LiGaSe2 [4] | Pna21 | ||||||
LiGaTe2 [4] | 6.33757(2) | 6.33757(2) | 11.70095(5) | I43d | 940 [8] | 2.41 | |
LiInTe2 [9] | 6.398 | 6.398 | 12.46 | I42d | 4.91 | 1.5 [4] | |
CuAlS2 | 5.323 | 5.323 | 10.44 | I42d | 3.47 | 2500 | 2.5 |
CuAlSe2 | 5.617 | 5.617 | 10.92 | I42d | 4.70 | 2260 | 2.67 |
CuAlTe2 | 5.976 | 5.976 | 11.80 | I42d | 5.50 | 2550 | 0.88 |
β-CuGaO2 [3] | 5.46004(1) | 6.61013(2) | 5. 27417(1) | Pna21 | m | 1.47d | |
CuGaS2 | 5.360 | 5.360 | 10.49 | I42d | 4.35 | 2300 | 2.38 |
CuGaSe2 | 5.618 | 5.618 | 11.01 | I42d | 5.56 | 1970 | 0.96; 1.63 |
CuGaTe2 | 6.013 | 6.013 | 11.93 | I42d | 5.99 | 2400 | 0.82; 1.0 |
CuInS2 | 5.528 | 5.528 | 11.08 | I42d | 4.75 | 1400 | 1.2 |
CuInSe2 | 5.785 | 5.785 | 11.56 | I42d | 5.77 | 1600 | 0.86; 0.92 |
CuInTe2 | 6.179 | 6.179 | 12.365 | I42d | 6.10 | 1660 | 0.95 |
CuTlS2 | 5.58 | 5.58 | 11.17 | I42d | 6.32 | ||
CuTlSe2 | 5.844 | 5.844 | 11.65 | I42d | 7.11 | 900 | 1.07 |
CuFeO2 | 3.035 | 3.035 | 17.166 | R3m | 5.52 | ||
CuFeS2 | 5.29 | 5.29 | 10.32 | I42d | 4.088 | 1135 | 0.53 |
CuFeSe2 [10] | 5.544 | 5.544 | 11.076 | P42c | 5.41 | 850 | 0.16 |
CuLaS2 | 5.65 | 5.65 | 10.86 | I42d | |||
β-AgAlO2 | m | 2.8i | |||||
AgAlS2 | 5.707 | 5.707 | 10.28 | I42d | 3.94 | ||
AgAlSe2 | 5.986 | 5.986 | 10.77 | I42d | 5.07 | 1220 | 0.7 |
AgAlTe2 | 6.309 | 6.309 | 11.85 | I42d | 6.18 | 1000 | 0.56 |
α-AgGaO2 | P63mc | 4.12d [11] | |||||
β-AgGaO2 | Pna2a | m | 2.2i | ||||
AgGaS2 | 5.755 | 5.755 | 10.28 | I42d | 4.72 | 1.66 | |
AgGaSe2 | 5.985 | 5.985 | 10.90 | I42d | 5.84 | 1120 | 1.1 |
AgGaTe2 | 6.301 | 6.301 | 11.96 | I42d | 6.05 | 990 | 1.32 [4] |
AgInS2 | 5.828 | 5.828 | 11.19 | I42d | 5.00 | 1.18 | |
AgInSe2 | 6.102 | 6.102 | 11.69 | I42d | 5.81 | 1053 | 0.96; 0.52 |
AgInTe2 | 6.42 | 6.42 | 12.59 | I42d | 6.12 | 965 | 1.03 [4] |
AgFeS2 | 5.66 | 5.66 | 10.30 | I42d | 4.53 | 0.88 [12] |
In inorganic chemistry and materials chemistry, a ternary compound or ternary phase is a chemical compound containing three different elements.
Copper indium gallium (di)selenide (CIGS) is a I-III-VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide (often abbreviated "CIS") and copper gallium selenide. It has a chemical formula of CuIn1−xGaxSe2, where the value of x can vary from 0 (pure copper indium selenide) to 1 (pure copper gallium selenide). CIGS is a tetrahedrally bonded semiconductor, with the chalcopyrite crystal structure, and a bandgap varying continuously with x from about 1.0 eV (for copper indium selenide) to about 1.7 eV (for copper gallium selenide).
In nanotechnology, nanorods are one morphology of nanoscale objects. Each of their dimensions range from 1–100 nm. They may be synthesized from metals or semiconducting materials. Standard aspect ratios are 3-5. Nanorods are produced by direct chemical synthesis. A combination of ligands act as shape control agents and bond to different facets of the nanorod with different strengths. This allows different faces of the nanorod to grow at different rates, producing an elongated object.
Zinc telluride is a binary chemical compound with the formula ZnTe. This solid is a semiconductor material with a direct band gap of 2.26 eV. It is usually a p-type semiconductor. Its crystal structure is cubic, like that for sphalerite and diamond.
Silver selenide (Ag2Se) is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na2SeO3) as one of its active ingredients, which is the source of the selenide (Se2−) anion combining with the silver in the toning process.
Silver molybdate (Ag2MoO4), a chemical compound, is a yellow, cubic crystalline substance often used in glass. Its crystals present two types of electronic structure, depending on the pressure conditions to which the crystal is subjected. At room temperature, Ag2MoO4 exhibits a spinel-type cubic structure, known as β-Ag2MoO4, which is more stable in nature. However, when exposed to high hydrostatic pressure, the tetragonal α-Ag2MoO4 forms as a metastable phase.
Gallium(III) oxide is an inorganic compound and ultra-wide-bandgap semiconductor with the formula Ga2O3. It is actively studied for applications in power electronics, phosphors, and gas sensing. The compound has several polymorphs, of which the monoclinic β-phase is the most stable. The β-phase’s bandgap of 4.7–4.9 eV and large-area, native substrates make it a promising competitor to GaN and SiC-based power electronics applications and solar-blind UV photodetectors. The orthorhombic ĸ-Ga2O3 is the second most stable polymorph. The ĸ-phase has shown instability of subsurface doping density under thermal exposure. Ga2O3 exhibits reduced thermal conductivity and electron mobility by an order of magnitude compared to GaN and SiC, but is predicted to be significantly more cost-effective due to being the only wide-bandgap material capable of being grown from melt. β-Ga2O3 is thought to be radiation-hard, which makes it promising for military and space applications.
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.
A copper indium gallium selenide solar cell is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper indium gallium selenide solid solution on glass or plastic backing, along with electrodes on the front and back to collect current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.
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.
Two-photon photovoltaic effect is an energy collection method based on two-photon absorption (TPA). The TPP effect can be thought of as the nonlinear equivalent of the traditional photovoltaic effect involving high optical intensities. This effect occurs when two photons are absorbed at the same time resulting in an electron-hole pair.
Solar Frontier Kabushiki Kaisha is a Japanese photovoltaic company that develops and manufactures thin film solar cells using CIGS technology. It is a fully owned subsidiary of Showa Shell Sekiyu and located in Minato, Tokyo, Japan. The company was founded in 2006 as Showa Shell Solar, and renamed Solar Frontier in April 2010.
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Ogtay Abiloglu Samadov or Samedov is an Azerbaijani nuclear physicist who since 2015 has been director of the Institute of Radiation Problems of Azerbaijan National Academy of Sciences.
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