Se Flux Research Articles

Sn-Se Binary and Cu-Sn-Se Ternary Thin Films Grown by Co-Evaporation Process

Unfavorable secondary phases like binaries and ternaries are often observed in synthesizing Cu2ZnSnSe4 (CZTSe) quaternary crystal due to its narrow phase space, which strongly limits the performance of Kesterite solar cells. To identify the growth parameters against the stability of these secondary phases, we systematically studied the growth process of Sn-Se binaries and Cu-Sn-Se ternaries using co-evaporation method. We found that the compositions of Sn-related binary and ternary phases were strongly dependent on the substrate temperature and Se flux during deposition, which will be helpful in designing formation paths for quaternary system. Growth temperature of CZTSe higher than 490 °C will make the thin film free of Cu2SnSe3 phase. Our experiments also suggest that formation pathways in the Cu2SnSe3-ZnSe pseudobinary phase diagram at a slightly lower substrate temperature deserve more experimental and theoretical considerations because of its easier composition control.

Structural tuning of wide-gap chalcopyrite CuGaSe2 thin films and highly efficient solar cells: differences from narrow-gap Cu(In,Ga)Se2

Simultaneous realization of high values of open circuit voltage (Voc), fill factor (FF), and energy conversion efficiency (η) in wide-gap CuGaSe2 (CGS) solar cells has long been one of the most challenging issues in the realm of chalcopyrite photovoltaics. In this communication, structural tuning of CGS thin films by means of controlling the amount of Se flux used during CGS film growth and improvements in solar cell performance (Voc > 0.9 V, FF > 0.7, and η > 10%) are demonstrated. Systematic variations in CGS film properties with the Se flux and correlation with device properties are shown. The unique CGS thin-film growth kinetics, which are different from narrow-gap Cu(In,Ga)Se2, are also presented and discussed. This development of double digit efficiency for CGS solar cells opens a new frontier for the broad application of a new class of chalcopyrite-based devices. Copyright © 2014 John Wiley & Sons, Ltd.

A comparison between thin film solar cells made from co‐evaporated CuIn1‐xGaxSe2 using a one‐stage process versus a three‐stage process

AbstractUntil this day, the most efficient Cu(In,Ga)Se2 thin film solar cells have been prepared using a rather complex growth process often referred to as three‐stage or multistage. This family of processes is mainly characterized by a first step deposited with only In, Ga and Se flux to form a first layer. Cu is added in a second step until the film becomes slightly Cu‐rich, where‐after the film is converted to its final Cu‐poor composition by a third stage, again with no or very little addition of Cu. In this paper, a comparison between solar cells prepared with the three‐stage process and a one‐stage/in‐line process with the same composition, thickness, and solar cell stack is made. The one‐stage process is easier to be used in an industrial scale and do not have Cu‐rich transitions. The samples were analyzed using glow discharge optical emission spectroscopy, scanning electron microscopy, X‐ray diffraction, current–voltage‐temperature, capacitance‐voltage, external quantum efficiency, transmission/reflection, and photoluminescence. It was concluded that in spite of differences in the texturing, morphology and Ga gradient, the electrical performance of the two types of samples is quite similar as demonstrated by the similar J–V behavior, quantum spectral response, and the estimated recombination losses. Copyright © 2014 John Wiley & Sons, Ltd.

Molecular beam epitaxy of single unit-cell FeSe superconducting films on SrTiO3(001)

Based on our previous work, we have systematically investigated the molecular beam epitaxy growth of single unit-cell FeSe films on SrTiO3(001) substrates and studied the surface morphology by scanning tunneling microscopy. We found that there are three key steps to obtain large-scale uniform one unit-cell superconducting FeSe films. First, the STO(001) substrates should be treated by HCl etching and thermal annealing under oxygen flux so that a specific TiO2-terminated STO(001) surface with well-defined step-terrace structure could be obtained. Second, the Fe and Se fluxes and substrate temperature have to be controlled delicately. At last, post-growth annealing is also critical, which can remove extra Se adatoms, and more importantly facilitate the necessary electron transfer for superconductivity transition.

The origin and geochemical cycle of soil selenium in a Se-rich area of China

Mianyang City, located in the Fujiang River Basin, Sichuan Province, is a Se-rich area of China. The distribution of Selenium (Se) in the Mianyang area was studied based on assay data obtained from soil, irrigation water, fertilizer, and rice (grain and stem) samples. The ratio between natural and anthropogenic sources in the area was derived by analyzing the concentrations and spatial distributions of multiple elements (such as Se, cadmium, arsenic, and mercury) in the soil. The controlling factors affecting Se concentration in the soil were also investigated. We established a geochemical model of the Se cycle among the different media (i.e., the atmosphere, water, soils, and plants). We then calculated the annual Se flux caused by various inputs' (such as precipitation, fertilization, and irrigation) and outputs' (such as infiltration, crop harvest, removal of straws from cropland, and volatilization) pathways in the topsoil. We discuss the contribution of different pathways to the Se cycle and provide evidence for exploring Se-rich land in the study area.

The growth of Cu2 − xSe thin films using nanoparticles

For low-cost fabrication applications, Cu2−xSe thin films were fabricated by a non-vacuum process and were then characterized in terms of quality. Cu–Se nanoparticles were synthesized by a low-temperature colloidal method and were confirmed to be Cu2−xSe nanoparticles by X-ray diffraction and Raman spectroscopy. The synthesized Cu2−xSe nanoparticles were deposited as films by a direct non-vacuum coating method, and the as-deposited Cu2−xSe thin films were selenized at different reaction temperatures, reaction times, and Se fluxes. The selenized films presented several distinct characteristics that depended on their fabrication conditions. Well-grown Cu2−xSe thin films were obtained at high reaction temperatures, long reaction times, and high Se fluxes. In addition, the selenized Cu2−xSe layer was observed to have a larger Cu content than the Cu2−xSe nanoparticles.

Impact of Se flux on the defect formation in polycrystalline Cu(In,Ga)Se2 thin films grown by three stage evaporation process

Cu(InxGa1−x)Se2 (CIGS) films, grown under various Se fluxes, have been investigated by the positron annihilation spectroscopy. The line-shape parameter (S) of the positron annihilation spectra was used to characterize the defects in the CIGS films. When Se flux was decreased, the S parameter at the surface and subsurface region of the films increased. This phenomenon was attributed to the increased concentration of the defect complex formed between Se and Cu vacancies. S parameter at the surface region was significantly higher than that in the bulk region of each film. It was explained with the model of compositional inhomogeneities along the depth of the film. Solar cell performance strongly correlated to the S parameter at the surface region of the CIGS films. Sufficient Se flux was found to be effective to reduce the S parameter, thereby, to suppress the defects in the films.

Reactive Sputtering Process for CuIn<sub>1-x</sub>Ga<sub>x</sub>Se<sub>2</sub> Thin Film Solar Cells

CuIn1-xGaxSe2 (CIGS) thin films are grown on Mo/soda lime glass using a reactive sputtering process in which a Se cracker is used to deliver reactive Se molecules. The Cu and (In0.7Ga0.3)2Se3 targets are simultaneously sputtered under the delivery of reactive Se. The effects of Se flux on film composition are investigated. The Cu/(In+Ga) composition ratio increases as the Se flux increases at a plasma power of less than 30 W for the Cu target. The (112) crystal orientation becomes dominant, and crystal grain size is larger with Se flux. The power conversion efficiency of a solar cell fabricated using an 800-nm CIGS film is 8.5%.

The role of growth temperature and Se flux on Cu(In,Ga)Se2 thin film deposited on a stainless steel substrate and solar cell

The role of growth temperature and Se flux on Cu(In,Ga)Se2 (CIGS)/Mo deposited on stainless steel substrates without a barrier is investigated by combined use of secondary ion mass spectroscopy, scanning electron microscopy and Raman spectroscopy. Fe atoms diffuse into the CIGS film with an increasing slope toward the CIGS front surface and the CIGS/Mo interface at 500 °C. High Se flux can increase the grain size and depress the formation of group III-rich phases on the surface and grain boundaries of the CIGS film, reducing Fe content in the surface region of the CIGS film and grain boundaries, which results in the increase of open circuit voltage (Voc) and fill factor (FF). Meanwhile, Jsc also significantly increases for high Se flux. In this case, a 12.1%-efficient CIGS solar cell on stainless steel without a diffusion barrier and Na supply is obtained. The influence of diffusing Fe on a solar cell with different Se fluxes is further discussed in detail.

ChemInform Abstract: Two New Ternary Lanthanide Antimony Chalcogenides: Yb4Sb2S11.25 and Tm4Sb2Se11.68 Containing Chalcogenide Q2‐ and Dichalcogenide (Q2)2‐ Anions.

AbstractDark red crystals of Yb4Sb2S11.25 (25% yield) and dark brown crystals of Tm4Sb2Se11.68 are prepared by reaction of the elements in an in‐situ‐Sb2Q3/NaBr (Q: S, Se) flux at 900 °C.

Two new ternary lanthanide antimony chalcogenides: Yb4Sb2S11.25 and Tm4Sb2Se11.68 containing chalcogenide Q2− and dichalcogenide (Q2)2− anions

Dark red and dark brown crystals of Yb4Sb2S11.25 and Tm8Sb4Se11.68, respectively, were obtained from the reaction of the elements in Sb2Q3 (Q=S, Se) fluxes. Both non-stoichiometric compounds are orthorhombic and crystallize in the same space group Pnnm, with two formula units per unit cell (a=12.446(2), b=5.341(1), c=12.058(2) for sulfide and a=13.126(2), b=5.623(1), c=12.499(2) for the selenide). Their crystal structures are dominated by lanthanide-chalcogenide polyhedra (CN=7 and 8), which share corners, edges, triangular- and square-faces to form a three-dimensional framework embedding antinomy cations. The latter are coordinated by three sulfide anions with 5(1+2+2) secondary contacts forming basically infinite chains running along [010]. The chalcogens in both compounds form chalcogenide Q2− and dichalcogenide (Q2)2− anionic units. The optical analysis made on those compounds shows that both are semiconductors with band gap of 1.71 and 1.22eV for Yb4Sb2S11.25 and Tm4Sb2Se11.75, respectively.

Texture and morphology variations in (In,Ga)2Se3 and Cu(In,Ga)Se2 thin films grown with various Se source conditions

ABSTRACTTexture and morphology variations in co‐evaporated (In,Ga)2Se3 and Cu(In,Ga)Se2 (CIGS) films grown with various Se source conditions during growth were studied. The Se species of simply evaporated, large molecular Se (E‐Se, low‐sticking coefficient), and RF‐plasma cracked atomic Se (R‐Se, high sticking coefficient) were used in the present work. (In,Ga)2Se3 precursor films, which were prepared during the first stage of CIGS film growth by the three‐stage process, showed systematic variations in texture and Na distribution profile with varying evaporative Se (E‐Se) flux. The properties of CIGS films and solar cells also showed systematic variations, and the open‐circuit voltage (Voc) and fill factor were found to be especially sensitive to the E‐Se flux. R‐Se grown (In,Ga)2Se3 precursor films featured granular morphology with strong (105) and (301) peaks in the diffraction pattern, and the texture was very similar to an E‐Se grown film fabricated with a Se to group III metal (In + Ga) flux ratio (P[Se]/[In + Ga]) of about 6, although the nominal P[Se]/[In + Ga] used for an R‐Se source was very small and less than 0.5. The R‐Se grown CIGS films displayed, however, highly dense surfaces and larger grain sizes than E‐Se grown CIGS films. The controllability of film morphology and the Na diffusion profile in (In,Ga)2Se3 and CIGS films with various Se source conditions are discussed. Copyright © 2011 John Wiley & Sons, Ltd.

Effect of Se flux on CuIn1‐xGaxSe2 film in reactive sputtering process

ABSTRACTCuIn1‐xGaxSe2 (CIGS) thin films were grown on Mo/soda lime glass using a reactive sputtering process in which a Se cracker was used to deliver reactive Se molecules. The Cu0·6 Ga0·4 and Cu0·4In0·6 targets were simultaneously sputtered under the delivery of reactive Se. The effects of Se flux on CIGS film deposition were investigated. The CIGS film growth rate decreased, and the surface roughness of a film increased as the Se flux increased. The [112] crystal orientation was dominant, and metallic crystal phases such as Cu9Ga4 and Cu16In9 in a film were disappearing with increasing Se flux. A solar cell fabricated using a 900‐nm CIGS film showed the power conversion efficiency of 8·6%, the highest value found in a sub‐micron thick CIGS solar cell related to a reactive sputtering process with metallic targets. Copyright © 2011 John Wiley & Sons, Ltd.

ChemInform Abstract: Syntheses, Structure, Magnetism, and Optical Properties of the Ordered Interlanthanide Copper Chalcogenides Ln2YbCuQ5 (Ln: La, Ce, Pr, Nd, Sm; Q: S, Se): Evidence for Unusual Magnetic Ordering in Sm2YbCuS5.

AbstractThe black title compounds are synthesized by reactions of the elements in Sb2Q3 (Q: S, Se) fluxes at 900 °C for 7 d and characterized by single crystal XRD, UV/VIS/NIR diffuse reflectance spectroscopy, and magnetic susceptibility measurements.

Syntheses, Structure, Magnetism, and Optical Properties of the Ordered Interlanthanide Copper Chalcogenides Ln2YbCuQ5 (Ln = La, Ce, Pr, Nd, Sm; Q = S, Se): Evidence for Unusual Magnetic Ordering in Sm2YbCuS5

Ln2YbCuQ5 (Ln = La, Ce, Pr, Nd, Sm; Q = S, Se) have been prepared by direct reaction of the elements in Sb2Q3 (Q = S, Se) fluxes at 900 °C. All compounds have been characterized by single-crystal X-ray diffraction methods and are isotypic. The structure of Ln2YbCuQ5 consists of one-dimensional ∞1[YbCuQ5]6− ribbons extending along the b-axis that are connected by larger Ln3+ ions. Each ribbon is constructed from two single chains of [YbQ6] octahedra with one double chain of [CuQ5] trigonal bipyramids in the middle. All three chains connect with each other via edge-sharing. There are two crystallographically unique Ln atoms, one octahedral Yb site, and two disordered Cu positions inside of distorted Q5 trigonal bipyramids. Both Ln atoms are surrounded by eight Q atoms in bicapped trigonal prisms. The magnetic properties of Ln2YbCuQ5 have been characterized using magnetic susceptibility and heat capacity measurements, while their optical properties have been explored using UV−vis−NIR diffuse reflectance spec...

Biosyntheis of bioactive seleno-compunds in Saccharomyces cerevisiae via metabolic and bioprocess engineering

Selenium (Se) is an essential element for many organisms as it is present under the form of Se-cysteine in Se-proteins. The main sources of Se for animals are edible plants able to accumulate Se from the soil and store it under organic forms. Some of Se organic forms bioavailable for animals, such as Se-methyl-selenocysteine (SeMCys), have been proven to have cancer-preventing effects if regularly introduced into the diet. Since Se content in plants is highly susceptible to environmental factors, the intake of Se is often insufficient to result in beneficial effects. Therefore, the use of Se-enriched yeast as food supplement is made available to avoid Se shortage. The yeast Saccharomyces cerevisiae does not require Se as essential element, but is able to metabolise and accumulate Se. This work shows a study of Se-metabolism in yeast that lead to the definition of a metabolic engineering strategy and to an optimized bioprocess to increase the levels of beneficial Se-compounds in yeast. After a preliminary study on Se uptake dynamics and Se-metabolite profile in yeast, a recombinant yeast strain was generated, by introducing heterologous genes from plants belonging to Brassicaceae and Fabaceae families. Due to the delicate balance between toxic and beneficial effects of Se, the cultivation process was carefully optimized in terms of medium composition and Se feeding. The established bioprocess allowed minimizing the toxicity of Se and redirecting Se fluxes towards the biosynthesis of SeMCys at the same time. The results obtained demonstrate that the coupling of genetic engineering strategies with optimization of cultivation system is a promising approach for the establishment of a yeast cell factory for the production of yeast enriched in health promoting Se-compounds.

Properties of Cu(In,Ga)Se2 Thin Film by Co-Evaporation

Cu(In,Ga)Se2 (CIGS) compound, which has high optical absorption coefficient as direct transition type semiconductor, is very suitable for thin film solar cell due to its high thermal stability and moisture tolerance as well as its low fabrication cost compared to the standard crystalline Si solar cell. In this research, it was tried to control the absorption capability of CIGS layer by changing Ga/(In + Ga) ratio. The composition of film was changed by controlling the effusion-cell temperature of Cu, In, Ga at a fixed Se flux. Each sample was analyzed by using SEM (scanning electron microscope), EDS (energy dispersive spectroscopy), XRD (X-ray diffractometer) to confirm the optimum composition ratio of Cu/(In + Ga) = 0.82∼0.95, Ga/(In + Ga) = 0.26∼0.31, Cu/Se = 0.5.

Formation of the chemical composition of transition metal dichalcogenide thin films at pulsed laser deposition

The formation of the chemical composition of dichalcogenide films at pulsed laser deposition in vacuum and in rarefied gases (Ar, H2 ) is investigated with MoSe x thinfilm coatings. It is found that deposi� tion in gases increases the selenium concentration and somewhat flattens the composition over the substrate surface. To elucidate the mechanisms underlying the MoSex film formation, a computer model is used that simulates the motion of a pulsed laserinitiated atomic flux through a rarefied gaseous medium. Using this model, the energy and angular parameters of atomic Mo and Se fluxes toward the substrate are calculated. It is shown that the expansion dynamics of laser plume components (Mo and Se) and the selective sputtering of selenium are the main factors governing the formation of the chemical composition and its distribution over the substrate. The influence of the sort of gas on the efficiency of atomic flux slowdown and scattering and on material losses during deposition is considered.

Determination of Cu(In 1− xGa x) 3Se 5 defect phase in MBE grown Cu(In 1− xGa x)Se 2 thin film by Rietveld analysis

Quantitative phase analysis of Cu(In 1− x Ga x )Se 2 (CIGS) thin film grown over Mo coated soda lime glass substrates was studied by Rietveld refinement process using room temperature X-ray data at θ–2 θ mode. Films were found to contain both stoichiometric Cu(In 1− x Ga x )Se 2 and defect related Cu(In 1− x Ga x ) 3Se 5 phases. Best fitting was obtained using crystal structure with space group I-42d for Cu(In 1− x Ga x )Se 2 and I-42m for Cu(In 1− x Ga x ) 3Se 5 phase. The effects of Ga/III (=Ga/In+Ga= x) ratio and Se flux during growth over the formation of Cu(In 1− x Ga x ) 3Se 5 defect phase in CIGS was studied and the correlation between quantity of Cu(In 1− x Ga x ) 3Se 5 phase and solar cell performance is discussed.

CuInSe2 (CIS) Thin Film Solar Cells by Direct Coating and Selenization of Solution Precursors

CuInSe2 (CIS) absorber layer was formed by a direct nonvacuum coating and a subsequent selenization of precursor solutions of Cu(NO3)2 and InCl3 dissolved in methanol. The viscosity of precursor solutions was adjusted by adding ethyl-cellulose (EC) to be suitable for the doctor-blade coating. During the coating and drying process Cu2+ ions in the starting solution were reduced to Cu+, resulting in precursor films consisting of CuCl crystals and amorphous In compound embedded in EC matrix. Selenization of the precursor films with Se vapor at elevated temperature generated double-layered films with an upper layer of chalcopyrite CIS and a carbon residue bottom layer. Significant In loss was observed during the selenization, which was attributed to the evaporation of the In2Se binary phase, confirmed by investigating the change in the Cu/In ratio of the selenized film as a function of Se flux and substrate temperature. As a proof-of-concept, thin film solar cells were fabricated with the double-layered absorber film and the devices exhibited reproducible conversion efficiency as high as about 2%.