Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.

Deep eutectic solvents: syntheses, properties and applications

Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Solution-processed hybrid organic–inorganic perovskites (HOIPs) exhibit long electronic carrier diffusion lengths, high optical absorption coefficients and impressive photovoltaic device performance. Recent results allow us to compare and contrast HOIP charge-transport characteristics to those of III–V semiconductors — benchmarks of photovoltaic (and light-emitting and laser diode) performance. In this Review, we summarize what is known and unknown about charge transport in HOIPs, with particular emphasis on their advantages as photovoltaic materials. Experimental and theoretical findings are integrated into one narrative, in which we highlight the fundamental questions that need to be addressed regarding the charge-transport properties of these materials and suggest future research directions. The charge transport properties of hybrid organic—inorganic perovskites, which can explain their excellent photovoltaic performance, are reviewed through an integrated summary of experimental and theoretical findings. The potential origins of these properties are discussed and future research directions are indicated.

Hybrid organic—inorganic perovskites: low-cost semiconductors with intriguing charge-transport properties

Chalcopyrite thin film solar cells by electrodeposition

WS2/CdS photocatalysts with different amounts of WS2 cocatalyst are prepared by loading WS2 on CdS with an impregnation–sulfidation approach. The transformation process of the tungsten species loaded on CdS together with the junctions formed between WS2 and CdS are clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. Photocatalytic H2 production on WS2/CdS catalysts under visible light (λ > 420 nm) shows that WS2 cocatalyst plays a crucial role in H2 production. Under optimum conditions, the rate of H2 evolution can be increased by up to 28 times when CdS was loaded with only 1.0 wt % WS2, and WS2 demonstrates a catalytic performance comparable or even superior to those of noble metals. Photocatalytic reaction results and electrochemical measurements indicate that the significantly enhanced H2 evolution of WS2/CdS catalyst mainly owns to the junctions formed between WS2 and CdS and the excellent performance of WS2 as a cocatalyst in catalyzing H2 evolution.

Photocatalytic H2 Evolution on CdS Loaded with WS2 as Cocatalyst under Visible Light Irradiation

Copper indium gallium diselenide layers with p(+), p, i, n, and n(+)-type electrical conduction, as predetermined, have been electrodeposited from aqueous solutions in a single bath. The photoelectrochemical cell has been used as the key analytical tool to determine the electrical conduction type, and X-ray fluorescence has been used to determine the stoichiometry of the corresponding layers. Optical absorption, X-ray diffraction, and atomic force microscopy have been used to investigate the bandgap, bulk structure, and surface morphology of the material layers, respectively. It has been found that the bandgaps of these layers can be varied in the range 1.10-2.20 eV. A four-layer n-n-i-p solar cell structure was fabricated and a corresponding energy band diagram for the device constructed. Current-voltage and capacitance-voltage measurements were carried out to assess the devices, and these parameters (V-oc approximate to 570 mV, J(sc)approximate to 36 mA cm(-2), and FF approximate to 0.40) indicate encouraging characteristics enabling further development of multilayer thin-film solar cells based on CuInGaSe2. The addition of a p(+) layer to the structure improved device parameters as expected due to improvements at the metal contact to the p(+) surface of the n-n-i-p-p(+) structure. (c) 2007 The Electrochemical Society.

Development of p + , p, i, n, and n + -Type CuInGaSe2 Layers for Applications in Graded Bandgap Multilayer Thin-Film Solar Cells

Experimental study of graded bandgap Cu(InGa)(SeS)2 thin films grown on glass/molybdenum substrates by selenization and sulphidation

Effects of multi-defects at metal/semiconductor interfaces on electrical properties and their influence on stability and lifetime of thin film solar cells

ZnSe layers have been grown by a low temperature (∼65 °C) electrochemical deposition technique in an aqueous medium. The resulting thin films have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive analysis by X-rays (EDAX), glow discharge optical emission spectroscopy (GDOES) and X-ray fluorescence (XRF) for bulk material properties. A photo-electrochemical (PEC) cell and an optical absorption method have been used for determination of the electrical and optical properties of the thin films. XRD patterns indicate the growth of ZnSe layers with (1 1 1) as the preferred orientation. The XPS spectra are similar to those of commercially available ZnSe and the EDAX, GDOES and XRF also indicate the presence of Zn and Se in the layers. PEC studies show p-type semiconducting properties for the as deposited layers and n-type ZnSe can be produced by appropriate doping. Optical absorption is maximum around 460 nm indicating a band gap of 2.7 eV. Annealing at 200 °C for 15 mins improves both the crystallinity of the layers and the photoresponse of the electrolyte/ZnSe liquid/solid Schottky junction. © 1998 Chapman & Hall

Growth of n-type and p-type ZnSe thin films using an electrochemical technique for applications in large area optoelectronic devices

Intrinsic zinc oxide (i-ZnO) and aluminium-doped ZnO (ZnO:Al) are components of high-efficiency copper indium gallium diselenide solar cells. This paper examines both of these materials grown by two different techniques, namely radio frequency sputtering and electrodeposition (ED) for comparison and a better understanding. X-ray diffraction showed all materials to be polycrystalline and hexagonal (wurtzite) ZnO. Scanning electron microscopy indicated crystallites with different orientations for ED materials compared to agglomerated nanocrystallites of the sputtered layers. The band-gap energy was determined to be in the range 3.27-3.45 eV. The transmission was 85% for both ED materials and 95% for the sputtered layers. Glass/FTO/i-ZnO/Al structures were rectifying, and glass/FTO/ZnO:Al/Al contacts were ohmic for both ZnO:Al layers. Addition of Al decreases the bulk resistivity for both i-ZnO layers by 1-2 orders of magnitude. The photovoltage response to pulsed illumination showed a slow relaxation hysteresis, and all materials showed n-type electrical conduction.

http://iopscience.iop.org/article/10.1088/0268-1242/23/12/125003/pdf

Anura Priyajith Samantilleke

Papers

Development of p + , p, i, n, and n + -Type CuInGaSe2 Layers for Applications in Graded Bandgap Multilayer Thin-Film Solar Cells

Experimental study of graded bandgap Cu(InGa)(SeS)2 thin films grown on glass/molybdenum substrates by selenization and sulphidation

Effects of multi-defects at metal/semiconductor interfaces on electrical properties and their influence on stability and lifetime of thin film solar cells

Growth of n-type and p-type ZnSe thin films using an electrochemical technique for applications in large area optoelectronic devices

Comparison of electrodeposited and sputtered intrinsic and aluminium-doped zinc oxide thin films