Tetragonal Chalcopyrite Structure Research Articles

A first principles investigation of the electronic, mechanical and optical properties of XPbN2 (X=Mg, Zn)

The electronic, mechanical, optical and conductive properties of MgPbN2 and ZnPbN2 are investigated using hybrid-functional first-principles calculations. Our calculations show that these two compounds preferentially stabilize in the tetragonal chalcopyrite structure. The calculated phonon dispersions show that both compounds are thermodynamically stable. From the calculated elastic constants we infer that the compound are also mechanically stable. As for the electronic properties, MgPbN2 is computed to be a semiconductor with a direct band gap of 1.071 eV at the Γ point, while ZnPbN2 is semi-metallic with the valence band and conduction band crossing at the Γ point. Both MgPbN2 and ZnPbN2 show an enhanced optical absorption and electric conductivity compared to those of the related semiconductors MgSnN2 and ZnSnN2. ZnPbN2 gives a much stronger electric conductivity and a slightly larger light absorption than MgPbN2. In addition the influence of alloying is investigated for Mg1−xZnxPbN2 at different doping amount. When Mg was doped at 25% level, a band gap of 0.22 eV opens up and turns the system to semiconducting. When Sn was doped at Pb site, a similar phenomena was observed. On the other hand, the electric conductivity will increase with a small amount of Zn doping in MgPbN2. With large amount of doping, a conductivity higher than that of pristine ZnPbN2 is achieved. Our investigation widens the knowledge of II-IV-N2 family of ternary nitrides, and may hence help to boost their applications.

Experimental and theoretical investigation of electronic and optical properties of CuAlxGa1−xTe2

The CuAlxGa1−xTe2 powders used in this study were made by planetary ball milling the source element powders (Cu, Al, Ga and Te). All of the produced powders and thin films were polycrystalline, with a tetragonal chalcopyrite structure with (112) orientation, according to XRD analysis. The structural and electronic features of the CuAlxGa1−xTe2 semiconductors were predicted using ab initio calculations based on Density Function Theory (DFT). The acquired results demonstrated that once the Al concentration increased, the lattice parameters and energy band gap changed in a way that was consistent with the experimental data.

Synthesis, characterization and stability study of aqueous MPA capped CuInS2/ZnS core/shell nanoparticles

Ternary I–III–VI nanoparticles (NPs) emerged as potential alternatives to II-VI group NPs. At present, it remains a tremendous challenge to directly synthesize high-quality CuInS2/ZnS (CIS/ZnS) core/shell NPs in aqueous solution at atmospheric pressure. Herein, a simple and reliable strategy that combines the hydrothermal method and successive ion layer adsorption and reaction has been proposed to realize the aqueous synthesis of fluorescent CIS/ZnS core/shell NPs. XRD depicts the formation of tetragonal chalcopyrite structure of CIS quantum dots (QDs). As synthesized CIS QDs and CIS/ZnS NPs possess spherical symmetry with average diameter of 6.6 nm and 11.2 nm, respectively. FT-IR spectra confirms the capping of MPA on CIS and CIS/ZnS NPs. UV–Vis spectra of core QDs and core/shell NPs does not show any direct absorption peak. After the growth of ZnS shell over CIS QDs, the PL QY of NPs reach from 6.95% to 17.19%. The stability and behavior of core and core/shell NPs in different pH, has been studied from both absorption and PL observations. Maximum PL emission intensity is found at pH 6 for both core and core/shell NPs. PL QY of core/shell NPs reduces from 17.19% to 8.08% after two months of storage. These properties make them promising candidates for biological and optoelectronic applications.

Investigation of optoelectronic properties of AgIn1−xGaxY2 (Y = Se, Te) semiconductors

The electronic structure and optical properties of AgIn1−xGaxY2 (Y = Se, Te) are investigated using first-principles calculations based on density functional theory. Both the local density approximation (LDA) and generalized gradient approximation (GGA) are employed in the calculation. The crystal structure of ternary semiconductors is the tetragonal chalcopyrite structure with space group $${\text{I}}\overline{{4}} {\text{2d}}$$ . The lattice parameters a(A) and c(A) are found to vary with the change in Ga composition. The energy gap across the Fermi level in the density of states plots shows that these materials are semiconductors. To compute accurate energy gap values, the LDA + U method is adopted. The calculated elastic constants indicate that these compounds are mechanically stable at normal pressure. The semiconducting nature of these materials may prove their applications in solar cells and photovoltaic absorbers. The optical parameters such as dielectric function, electron energy loss function, refractive index and reflectivity are computed.

Large-scale aqueous synthesis of Cu(In,Ga)Se2 nanoparticles for photocatalytic degradation of ciprofloxacin

Novel large-scale aqueous synthesis of CIGS phase-pure nanoparticles with tetragonal chalcopyrite structure, uniform chemical composition, and excellent optical properties. Nanoparticles for innovative photocatalytic degradation of CIP contaminant.

Electrodeposited chalcopyrite CuInGaSe2 absorbers for solar energy harvesting

CuInGaSe2 (CIGS) based compound semiconductors are among the leading materials for photovoltaic applications. Pulsed current electrochemical deposition is employed in this study to fabricate CIGS films wherein deposition is carried out from an electrolyte consisting chlorides of copper, indium, gallium and selenous acid at a pH around 2.2. The process also uses trisodium citrate which plays the role of complexing agent and aids in narrowing the reduction potentials of elements thereby easing the optimization to obtain desired composition. The precursor films are annealed in Ar at 550 °C and are characterized comprehensively. Results unveil that CIGS films possess compact agglomerated particle like morphology with an average particle size of ≈500 nm, copper-poor stoichiometric composition, and tetragonal chalcopyrite structure devoid of any unwanted secondary phases. Optical studies yield the bandgap to be ≈1.2 eV. Photoelectrochemical performance ascertains the photoactivity of CIGS under illumination. The low-cost pulse electrodeposition for obtaining pure quality CIGS films, which is also scalable and can be a great choice for fabrication of economic solar cells.

Chalcopyrite ZnSnSb2: A Promising Thermoelectric Material.

Ternary compounds with a tetragonal chalcopyrite structure, such as CuGaTe2, are promising thermoelectric (TE) materials. It has been demonstrated in various chalcopyrite systems, including compounds with quaternary chalcopyrite-like structures, that the lattice parameter ratio, c/ a, being exactly 2.00 to have a pseudo-cubic structure is key to increase the degeneracy at the valence band edge and ultimately achieve high TE performance. Considering the fact that ZnSnSb2 with a chalcopyrite structure is reported to have c/ a close to 2.00, it is expected to have multiple valence bands leading to a high p-type zT. However, there are no complete investigations on the high temperature TE properties of ZnSnSb2 mainly because of the difficulty of obtaining a single-phase ZnSnSb2. In the present study, pure ZnSnSb2 samples with no impurities are synthesized successfully using a Sn flux-based method and TE properties are characterized up to 585 K. Transport properties and thermal analysis indicate that the structure of ZnSnSb2 remains chalcopyrite with no order-disorder transition and clearly show that ZnSnSb2 can be made to exhibit a high zT in the low-to-mid temperature range through further optimization.

Effects on magnetic properties and light absorption bandgaps of lattice distortions in CuIn1-xCoxSe2 chalcopyrites

Co doped CuInSe2 compounds have been synthesized by vacuum arc melting-vacuum solid sintering-mechanical milling technology, and their crystal structures, magnetic and light absorption properties have been systematically investigated by using X-ray diffraction, vibrating sample magnetometer and UV–Vis spectrophotometer. X-ray diffraction analyses show that CuIn1-xCoxSe2 (x = 0–0.2) crystallize in tetragonal chalcopyrite structure with a space group of I4¯2d. Co partly substitutes for In at the 4b site. The studies of magnetic properties show that CuIn1-xCoxSe2 (x = 0.1–0.3) show supermagnetic characteristics at room temperature with applying an external field. Co doping can adjust the light absorption bandgaps of CuIn1-xCoxSe2 from 1.25 to 1.53eV. These phenomena are revealed to be closely correlated with the lattice distortions induced by Co doping into CuInSe2. The magnetism of Co doped CuInSe2 is suggested to come from the double-exchange mechanism. The magnetic moment and light absorption bandgap depend upon the lattice distortions of (In,Co)Se4 and CuSe4 tetrahedrons, it shows that the magnetic moment is going up with the increase of Se-(In,Co) bond length and the decrease of (In,Co)Se-(In,Co) bond angle; the light absorption bandgap is going up with the increase of volume distortion of CuSe4 tetrahedron.

Tailoring sub-bandgap of CuGaS2 thin film via chromium doping by facile chemical spray pyrolysis technique

Tailoring sub-bandgaps using intermediate states or bands with wide bandgap semiconductors is a promising and novel technique for the application in high efficiency solar cells. Pure and chromium (Cr) doped chalcopyrite CuGaS2 (CGS) thin films were prepared by facile chemical spray pyrolysis technique and annealed in vacuum, nitrogen and argon atmospheres. Structural characterization confirmed that the prepared films are in tetragonal chalcopyrite structure with polycrystalline nature. No secondary phases were present in both pure and Cr doped CGS thin films. Presence of Cr ions was confirmed by X-ray photoelectron spectroscopy and energy dispersive analysis of X-rays analyses. The optical direct and sub band gap of pristine and Cr doped CGS thin films were measured from UV absorption data. It was revealed that the pure CGS film has a band gap of 2.40 eV sub-band gap values were observed at 2.25 and 2.15 eV for 1 and 2 wt% of Cr doping, respectively. These gaps can be ascribed to the formation of intermediate bands due to hybridization of Cr d-states into the host electronic structure. Meanwhile, photoconductivity study demonstrated the photo-electric activity of the intermediate bands in the Cr doped thin films.

Crystallographic, optical, and electronic properties of Li-doped CuIn(S,Se)2, (Cu,Li)In(S,Se)2

(Cu1−xLix)In(S1−ySey)2 (CLISSe) samples with 0.0 ≤ x ≤ 0.4 and y = 0.25, 0.50, and 0.75 were prepared by a mechanochemical process and sequential heating. The X-ray diffraction (XRD) peaks of the (Cu1−xLix)In(S1−ySey)2 shifted to the lower angle side by the substitution of Li atoms for Cu atoms. The solid solution limit of Li for Cu in (Cu1−xLix)In(S1−ySey)2 system widened with increasing Se content, y. The single-phase (Cu1−xLix)In(S1−ySey)2 samples were obtained for the compositions with 0.0 ≤ x ≤ 0.05 for y = 0.25, 0.0 ≤ x ≤ 0.20 for y = 0.50, and 0.0 ≤ x ≤ 0.30 for y = 0.75. The crystallographic parameters such as the lattice constants a and c, c/a, and the atomic coordinate of a S/Se atom for (Cu1−xLix)In(S1−ySey)2 were refined by Rietveld analysis using XRD data. Both the lattice constants a and c of the (Cu1−xLix)In(S1−ySey)2 with a tetragonal chalcopyrite structure increased with increasing Li content, x. The band gaps of (Cu1−xLix)In(S1−ySey)2 solid solutions widened with increasing Li content, x. To understand the band diagram of the solid solutions, the energy level of the valence band maximum (VBM) from the vacuum level was determined from the ionization energy measured by photoemission yield spectroscopy (PYS). The energy level of the conduction band minimum (CBM) was also determined by adding the band-gap energy to the VBM level. The VBM level of the (Cu1−xLix)In(S0.25Se0.75)2 solid solution decreased considerably with increasing Li content, x. The CBM level of the (Cu1−xLix)In(S1−ySey)2 solid solution was approximately constant. The Li doping in CuIn(S,Se)2 is useful for decreasing the VBM of the CuIn(S,Se)2 absorber and increasing the band-gap energy of the CuIn(S,Se)2 absorber without increasing the CBM level.

CuInTe2 thin films synthesis using one-step electrodeposition process: structural, optical, and electrical characterization

Polycrystalline CuInTe2 (CIT) films were grown onto ITO substrate by one-step electrodeposition technique using acidic aqueous solutions. In this study, the influence of the deposition time on CIT films properties was examined using six techniques, the X-ray diffraction, the scanning electron microscopy, the energy dispersive X-ray analysis, the optical transmittance, the Raman spectroscopy and the electrical properties measurements. The thickness of CuInTe2 films increases as the deposition time increases. The X-ray diffraction investigation of the films deposited during 5 and 10 min shows up only a tetragonal CuInTe2 chalcopyrite structure, with a preferred orientation along [112] direction. However, the films deposited during 15 and 20 min exhibits the CuInTe2 chalcopyrite structure as a main phase with In4Te3 as additional secondary phase. We have noticed a change in the preferred orientation axis of the prepared films as function of deposition time. The films show the direct allowed band gap and their energy band gap decreased from 1.06 to 0.99 eV as the deposition time increased from 5 to 20 min. Hall effect measurements show that the deposition time changes the conductivity type and films carrier concentration. The electrical conductivity is affected by the variation in the carrier mobility rather than by their concentration. The observed Raman modes in the films match well with those reported for single crystal CuInTe2 in the literature. All Raman spectra show the A1 mode at 127 cm−1 confirming the chalcopyrite crystalline quality of these films.

Hydrothermal synthesis of bright and stable AgInS2 quantum dots with tunable visible emission

Highly luminescent AgInS2 quantum dots (AIS QDs) were synthesized via hydrothermal method using L-glutathione (GSH) and sodium citrate (SC) as ligands. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) results confirmed that the AIS QDs have tetragonal chalcopyrite structure with good crystallinity, and the average diameter was about 3–5 nm. In addition, the obtained AIS QDs exhibited tunable photoluminescence (PL) spectra ranging from 575 nm to 650 nm and the quantum yield (QY) could reach up to 21.6% with the Ag/In ratio of 1:4 without further processing. Moreover, the experimental results demonstrated that the AIS QDs had long fluorescence lifetimes and excellent storage stability, indicating their promising applications in light-emitting diode (LED) and biological imaging fields.

Solution-liquid-solid growth of CuInTe2 nanowires as lithium-ion battery anodes

For the first time, CuInTe2 nanowires in I–III–VI2 chalcopyrite ternary system were synthesized via the bismuth (Bi)-seeded solution-liquid-solid (SLS) growth under 350°C. CuInTe2 nanowires were made by using the mixture of Cu(acac)2, InCl3 and Te powder as precursors, bismuth 2-ethylhexanoate [Bi[N(SiMe3)2]3] as growth seed solution and tri-n-octylphosphine (TOP) as solvents, respectively. As-made CuInTe2 nanowires are single crystals with a tetragonal chalcopyrite structure with diameters ranging from 10 to 200nm. In addition, as an anode material in the lithium ion batteries, the capacity of CuInTe2 nanowires in charging/discharging rate of 0.1C capacity of 780mAh/g after 200cycles (1C=572mAh/g), showing the accomplished reversibility. Furthermore, the discharge capacity (385mAh/g) at 5C rate is still higher than the theoretical capacity of graphite (372mAh/g), showing the attractive performance in the fast charging/discharging rates.

Structure and magnetic properties of CuIn1-xTxTe2 (T=Co,Mn)

The crystal structures, magnetic and optical properties of the 3d transition metals of Co or Mn doped CuInTe2 have been investigated using X-ray diffraction, magnetic measurements, ultraviolet and visible spectrophotometers. It is found that CuIn1-xTxTe2 (T=Co, Mn) crystallize in tetragonal chalcopyrite structure in a doping range of x=0-0.2. The structural analyses show that the 3d transition metal of Mn or Co prefers to occupy the 4b crystal position. Mn-doped CuIn1-xMnxTe2 (x=0-0.3) show paramagnetic characteristics at room temperature with the susceptibilities of about 10-5. However, lightly Co-doping into CuIn1-xCoxTe2 shows ferromagnetism at room temperature under a low applied field. This phenomenon is suggested to result from the spin-spin interactions between Co atoms which lead to the ferromagnetism. CuIn0.9Co0.1Te2 with ferromagnetism at room temperature under a low field revealed in this work indicates that it a good candidate for photovoltaic cells application since its bandgap matches well with that of CuIn1-xGaxSe2 with high conversion efficiency.

Facile synthesis of CuInS2 nanocrystals “photovoltaic ink” via hot-injection strategy under ambient environment

In this letter, oil-dispersed CuInS2 nanocrystals (CIS NCs) “photovoltaic ink” were successfully prepared using hot injection strategy under ambient environment, and different size of nanocrystals could be tailored through extending the reaction time. Series of analytical means were applied to characterize the obtained samples. The relative results revealed that the “copper rich” CIS NCs with a good monodispersity had tetragonal chalcopyrite structure; the size distribution of the samples tended to be widened along with extending reaction time, and the spectral absorption could also be regulated to cover most visible region. Finally, the obtained CIS NCs were sprayed as absorber in photovoltaic devices with the conventional configuration of (Glass/Mo/CIS/CdS/i-ZnO/AZO), and the best device exhibited promising power conversion efficiency of ~1.53% under AM 1.5g illumination.

Synthesis and formation mechanism of CuInSe2nanowires by one-step self-catalysed evaporation growth

High-quality CuInSe2 (CISe) nanowires have been prepared by a one-step evaporation process. The presented growth process results in a composite material consisting of CISe NWs on top of a polycrystalline CISe base layer. The nanowires were extensively characterized by transmission electron microscopy, confirming their composition and atomic-scale crystal structure with a very low number of structural defects. From these analyses, we infer that the growth axis is along the [111] direction. The polycrystalline base layer has a tetragonal chalcopyrite structure and is optically active as confirmed by X-ray diffraction and photoluminescence (PL) analysis, respectively. Potential applications of this composite CISe NW/base-layer material for photovoltaic energy conversion are supported by the reduced reflectivity of the material and its strong PL intensity. The presented growth method is based on elemental evaporation under vacuum conditions, which makes the process compatible with the fabrication of photovoltaic devices.

Synthesis, growth and characterization of AgInSe2 single crystals

Single crystal of the ternary semi-conductor AgInSe2 has been grown by Bridgman technique. The AgInSe2 crystal crystallizes in the tetragonal chalcopyrite structure. Using melt temperature oscillation method polycrystalline charge was synthesized. The synthesized charge was subjected to powder X-ray diffraction analysis. Thermal property of AgInSe2 was analyzed using differential scanning calorimetry (DSC) technique. The melting and solidification temperature is 777°C and 761°C respectively. The synthesized polycrystalline charge was employed to grow AgInSe2 single crystals. The grown crystal was confirmed by single crystal X-ray diffraction. The crystal exhibits 60% transmission in the Infrared region. The stoichiometric composition of AgInSe2 was confirmed by Energy dispersive X-ray analysis (EDAX). The electrical properties of the crystal were studied by Hall Effect measurements and photoconductivity.

Tin Incorporation in AgInSe2 Thin Films: Influence on Conductivity

Bipolarity with enhanced conductivity has been achieved by tin incorporation in AgInSe2 thin films. Structural and optical characterizations of these films prepared by reactive evaporation indicate that the incorporation neither distorts the tetragonal chalcopyrite structure nor affects the optical band gap of the parent compound. A detailed analysis of the low temperature conductivity of AgInSe2 (AIS) and tin incorporated AgInSe2 (AIS:Sn) suggests domination by variable range hopping, grain boundary effect, and thermal activation of carriers in different temperature regimes. The enhanced conductivity in AIS:Sn is attributed to donor and acceptor defect level formation, which has pushed the Fermi levels to ∼9 meV below the conduction band edge in n-type films and ∼3 meV above the valence band edge in p-type films. These improved characteristics of the films are likely to promote their suitability for photovoltaic and thermoelectric power generation applications.

Chemical bath deposition route for the synthesis of ultra-thin CuIn(S,Se)2 based solar cells

CuIn(S,Se)2 (CISSe) photovoltaic grade thin films are usually grown by expensive vacuum based methods or chemical routes that require highly toxic precursors. In this work, we present the synthesis of CISSe absorbers by a simple chemical bath deposition (CBD) route. In the first step, In2S3/Cu2−xS stack was deposited as a precursor by CBD on Mo-coated soda lime glass substrates, using respectively thioacetamide and N,N′-dimethylthiourea as S source. Then the CISSe thin films were synthesized by the precursor's selenization at 450°C. The obtained films were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The tetragonal chalcopyrite structure of CISSe was identified by XRD and Raman, confirming that the major part of S was replaced by Se. SEM images show a compact and homogeneous film and by cross-section the thickness was estimated to be around 700nm. Solar cells prepared with these absorbers exhibit an open circuit voltage of 369mV, a short circuit current density of 13.7mA/cm2, a fill factor of 45% and an efficiency of 2.3%.

X-ray diffraction studies on the effect of ball-milling speed on the structure of Cu(In,Ga)Se2 nanoparticles

Cu(In,Ga)Se2 (CIGS) semiconductors were prepared by arc melting and the vacuum solid reaction. CIGS nanoparticles were synthesized by the mechanical alloy method. The influences of various ball-milling speeds on phase structures for CIGS nanoparticles were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystal structures and unit-cell parameters of CIGS nanoparticles were determined using TREOR program and the least squares method. A Rietveld structural refinement was used to determine the atomic occupations and atomic numbers of CIGS prepared under various ball-milling speeds. The least size of agglomerated CIGS nanoparticles should be around 200 nm. CIGS nanoparticles milled at various milling speeds with a tetragonal chalcopyrite structure were obtained according to XRD analyses. However, Ga content in CIGS depends on milling speeds. Based on the structural refinements, the unit-cell parameters are a = 5.693(8)–5.744(9) Å and c = 11.334(9)–11.524(4) Å with gallium content ranging from 0.3 to 0.5. The atomic occupations are corresponding to the 4a crystal site for Cu atoms, the 4b site for In and the 8d site for Se. Ga prefers to occupy the 4b crystal site.