Chalcopyrite CuInSe2 Research Articles

The growth of heteroepitaxial CuInSe2 on free-standing N-polar GaN

We report that chalcopyrite CuInSe2 thin films were grown on free-standing N-polar GaN (0001̄) by molecular beam epitaxy. X-ray diffraction showed that the CuInSe2 thin film was grown in (112) orientation, and its peak of rocking curve with full width at half maximum of about 897.8 arc-sec indicated the epitaxial growth of CuInSe2 (112) film on N-polar GaN. Microstructure analysis of the CuInSe2 showed that the large lattice mismatch (28.5%) between CuInSe2 and GaN is accommodated by domain matching, and no interface reaction occurs between CuInSe2 and GaN. Our experimental results show that GaN is stable for the epitaxial growth of CuInSe2 thin film, which exhibits a promising potential for optoelectronic applications.

Colloidal Synthesis and Photocatalytic Performance of Size‐Controllable Solid or Hollow CuInSe2 Nanocrystals

AbstractMorphology evolution dependence on reaction time has been investigated to find a way to overcome polydispersity of the chalcopyrite CuInSe2 nanocrystals (NCs). A building–crumbling process is presented to understand the formation of small NCs. By carefully controlling magnetic stirring, ligand content, and duration, the polydispersity is fundamentally improved; thus solid and hollow spherical NCs and quantum dots can be easily obtained with tunable sizes. It is proposed that the NCs undergo Ostwald ripening induced morphology evolution from solid to hollow NCs. The photoelectric properties and photocatalytic activity have been investigated with TiO2 nanotube array based photoelectrodes. A maximum saturation photocurrent of 12.6 mA cm−2 has been achieved, and a structure‐dependent photocatalytic property has also been confirmed by using methyl orange as a model pollutant.

Hydrothermal synthesis of chalcopyrite CuInS2, CuInSe2 and CuInTe2 nanocubes and their characterization

CuInS2, CuInSe2 and CuInTe2 nanocubes of chalcopyrite structure have been successfully synthesized by hydrothermal process using deionized water as solvent at 180 °C for 20 h. The crystallinity, compositional, morphological and optical properties of the synthesized samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), Raman and photoluminescence (PL) spectra analyses. The Raman spectra of the synthesized CuInS2, CuInSe2 and CuInTe2 samples show the dominant A1 modes at 293, 172 and 121 cm−1 respectively. The possible chemical reaction and mechanism of nanocubes formation were discussed. The emission wavelength of as synthesized CuInS2, CuInSe2 and CuInTe2 samples were blue shifted at 746 nm (1.66 eV), 863 nm (1.43 eV) and 859 nm (1.44 eV) respectively.

Development of a high performance hollow CuInSe2nanospheres-based photoelectrochemical cell for hydrogen evolution

Hollow chalcopyrite CuInSe2 nanospheres are prepared by colloidal synthesis, for the first time, and assembled inside TiO2 nanotube arrays (NTAs) as a high performance photocatalyst for hydrogen evolution. In order to improve the charge separation, we engineer the CuInSe2-based photoelectrode with a novel strategy: thin layer ZnS (pre-treatment), hollow CuInSe2 nanocrystals, Mn-doped CdS, and thin layer ZnS (post-treatment) are assembled onto TiO2 NTAs in sequence. The Mn–CdS shell, closely packed around the earlier-modified CuInSe2 nanocrystals, provides high surface coverage to passivate surface states and enhance light absorption intensity. Double ZnS layers as a quasi-quantum well yield much longer electron diffusion length favoring a high photoresponse. Cyclic voltammetry (CV) is used to confirm the stepwise conduction band edge and electrochemically active surface areas. A type II-like core/shell heterojunction model is proposed to elucidate the charge transfer mechanism. Electrochemical impedance spectroscopy (EIS) and open-circuit dark–light–dark photovoltage response support a two-channel charge transport mechanism in this type of photoelectrode. Photoluminescence (PL) spectroscopy indicates a dramatically reduced electron transfer from TiO2 NTAs to the sensitizer. The saturated short circle photocurrent achieved by the quantum well structure photoelectrode under illumination of AM 1.5 (100 mW cm−2) is 22.4 mA cm−2. The corresponding measured hydrogen evolution rate is 7.93 ml cm−2 h−1.

Growth and characterization of chalcopyrite CuInSe2 nanoparticles

This work presents growth and characterization of copper indium diselenide (CuInSe2) nanoparticles with controllable size synthesized by a simple solvothermal process. Salts of copper(I), indium(III) and selenium powder have been used as starting precursors and ethylenediamine is used as a solvent. Nanoparticles synthesized at different temperatures have been analyzed using X-ray diffraction and transmission electron microscopy. Particle size has been calculated by dynamic light scattering. Surface morphology has also been studied by scanning electron microscopy. Optical properties of CuInSe2 provide band gap in the range of 0.94–1.05 eV, which are nearly close to optimal intensity for solar radiation suitable for solar cell devices.

Large scale and orientation-controllable nanotip structures on CuInS₂, Cu(In,Ga)S₂, CuInSe₂, and Cu(In,Ga)Se₂ by low energy ion beam bombardment process: growth and characterization.

One-step facile methodology to create nanotip arrays on chalcopyrite materials (such as CuInS2, Cu(In,Ga)S2, CuInSe2, and Cu(In,Ga)Se2) via a low energy ion beam bombardment process has been demonstrated. The mechanism of formation for nanotip arrays has been proposed by sputtering yields of metals and reduction of metals induced by the ion beam bombardment process. The optical reflectance of these chalcopyrite nanotip arrays has been characterized by UV-vis spectrophotometer and the efficient light-trapping effect has been observed. Large scale (∼4'') and high density (10(10) tips/cm(2)) of chalcopyrite nanotip arrays have been obtained by using low ion energy (< 1 kV), short processing duration (< 30 min), and template-free. Besides, orientation and length of these chalcopyrite nanotip arrays are controllable. Our results can be the guide for other nanostructured materials fabrication by ion sputtering and are available for industrial production as well.

Se-loss-induced CIS Thin Films in RTA Process after Co-sputtering Using CuSe2and InSe2Targets

Chalcopyrite CuInSe2 (CIS) thin films were prepared without Se- / S-containing gas by co-sputtering using CuSe2 and InSe2 selenide-targets and rapid thermal annealing. The grain size increased to a maximum of 54.68 nm with a predominant (112) plane. The tetragonal distortion parameter η decreased and the inter-planar spacing d(112) increased in the RTA-treated CIS thin films annealed at a 400°C, which indicates better crystal quality. The increased carrier concentration of RTA-treated p-type CIS thin films led to a decrease in resistivity due to an increase in Cu composition at annealing temperatures ≥ 350°C. The optical band gap energy (Eg) of CIS thin films decreased to 1.127 eV in RTA-treated CIS thin films annealed at 400°C due to the improved crystallinity, elevated carrier concentration and decreased In composition.

Structure and properties of electrodeposited films and film stacks for precursors of chalcopyrite and kesterite solar cells

A comparative analysis of the structure and surface morphology of copper, indium, tin, and zinc films and their layered compositions fabricated by electrochemical deposition in the galvanostatic steady-state mode, galvanostatic mode with the ultrasonic agitation of electrolytes, and forward and reverse pulsed modes with rectangular potential pulses is made. The effect of the electrodeposition modes on the structure, optical properties, and surface morphology of amorphous and crystalline selenium films is studied. Cu/In/Se and Cu/Sn/Zn/Se film compositions, which are model precursors of, respectively, chalcopyrite CuInSe2 and kesterite, are fabricated by successive electrochemical deposition. Upon being converted by subsequent annealings to CuInSe2 and Cu2ZnSnSe4 semiconductor materials, these precursors will be used as the base layers for a new generation of inexpensive high-efficiency thin-film solar cells.

Generalized stacking fault energies, cleavage energies, ionicity and brittleness of Cu(Al/Ga/In)Se2 and CuGa(S/Se/Te)2

We calculate the generalized stacking fault (GSF) energies and cleavage energies γcl of the chalcopyrite compounds CuAlSe2, CuGaSe2, CuInSe2, CuGaS2 and CuGaTe2 using first principles. From the GSF energies, we obtain the unstable stacking fault energies γus and intrinsic stacking fault energies γisf. By analyzing γus and γisf, we find that the (1 1 2) direction is the easiest slip direction for these five compounds. Also, for CuInSe2, it is most possible to undergo a dislocation-nucleation-induced plastic deformation along the (1 1 2) slip direction. We show that the (1 1 2) plane is the preferable plane for fracture in the five compounds by comparing γcl of the (0 0 1) and (1 1 2) planes. It is also found that both γus and γcl decrease as the cationic or anionic radius increases in these chalcopyrites, i.e. along the sequences CuAlSe2 → CuGaSe2 → CuInSe2 and CuGaS2 → CuGaSe2 → CuGaTe2. Based on the values of the ratio γcl/γus, we discuss the brittle–ductile properties of these compounds. All of the compounds can be considered as brittle materials. In addition, a strong relationship between γcl/γus and the total proportion of ionic bonding in these compounds is found.

Band Structure and Optical Properties of CuInSe&lt;sub&gt;2&lt;/sub&gt;

In this work, the electronic structure and dielectric function of chalcopyrite CuInSe2 are presented. The results are based on the full-potential linearized augmented plane wave (FPLAPW) method using the generalized gradient approximation (GGA) plus an onsite Coulomb interaction U of the Cu d states. The dielectric constant, absorption coefficient and refractive index are explored by means of optical response. The spin-orbit coupling effect is considered for the calculations of electronic structure and optical properties. We find that the results based on our calculation method have good agreement compared with experimental and other earlier simulations results.

Study of Size Distribution in Chalcopyrite Copper Indium (Di)selenide Nanoparticles

The copper indium diselenide compound (CuInSe2) belongs to the I-III-VI2 group and possesses a direct band gap. It was grown by a solvo-thermal process. In the present work, chalcopyrite CuInSe2 nanocrystalline particles were synthesized by using as starting precursors salts of In (III) and Cu (II). As-grown nanoparticles, were then characterized via powder X-ray diffraction (XRD), transmission electron microscope (TEM) and UV-VIS spectroscopy. Structural analysis done by powder X-ray diffraction reveal that CuInSe 2 nanocrystalline possess a tetragonally chalcopyrite structure. The microstructure analysis of the obtained product was done by transmission electron microscopy. The tunable optical properties and the bandgap of as grown material were studied by UV-Vis spectrometer. Finally, the effective mass approximation model was used to calculate the particle size from the effective band-gap energies.

Chemical bath composition effect on the properties of electrodeposited CuInSe2 thin films

Abstract Polycrystalline chalcopyrite CuInSe2 (CIS) thin films were deposited by electrodeposition technique onto ITO coated glass substrates. The used bath solution is formed by dissolution of CuCl2, InCl3, and SeO2 salts in de-ionized water, where the [Se]/[Cu + In] molar ratio is ranged from 0.4 to 1.3. The deposited films have been annealed at 300 °C for 30 min in argon atmosphere. The films structure and surface morphology characterizations were carried out respectively by means of X-ray diffraction method (XRD) and scanning electron microscope (SEM). XRD results indicate that CIS films having single phase chalcopyrite are obtained when the [Se]/[Cu + In] molar ratio is less than 1.3. While, for [Se]/[Cu + In] = 1.3, CuSe secondary phase is present together with CIS chalcopyrite phase. The crystallites were found to have a preferred orientation along (1 1 2) direction. The UV–visible optical transmittance measurements show that films absorption is due to allowed direct transition with a band gap ranged from 1.04 to 1.2 eV.

Synthesis of colloidal CuInSe2 nanoparticles by electrical spark discharge in liquid

This work presents a low-cost, non-vacuum, and facile process for fabrication of CuInSe2 (CIS) nanoparticles using electrical discharge treatment of mixture of copper, indium, and selenium powders between two tungsten electrodes immersed in pure ethanol. The synthesized particles were characterized by UV-Vis-NIR absorption, X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), Raman spectroscopy, transmission and scanning electron microscopy (TEM and SEM). TEM images exhibited that the final product is mainly composed of a large amount of primary nanoparticles typically 10–40 nm in diameter. The band gap energy value of the nanoparticles was estimated to be around 1.2 eV. The XRD pattern of the as-prepared samples besides the main peaks of chalcopyrite tetragonal CIS showed the diffraction peaks which could be attributed to intermediate phases. To omit the intermediate phases and reach to pure CIS nanoparticles the as-prepared in electrical discharge samples were annealed in vacuum at the temperature of 700 °C during 90 min. The XRD and SEM analysis results of annealed samples clearly indicated that chalcopyrite CuInSe2 particles with good crystallinity and near stoichiometric atomic composition were obtained. The composition and crystalline structure of the product was also confirmed by the room-temperature Raman spectrum showing an intense peak at 172 cm-1 corresponding to the A1 phonon mode of tetragonal CuInSe2 chalcopyrite.

Synthesis and reaction pathway investigation of chalcopyrite CuInSe2 nanoparticles for one-pot method

Highly dispersed and near stoichiometric chalcopyrite CuInSe2 nanoparticles were successfully synthesized via a facile and rapid one-pot method. For understanding the reaction pathway, the solid intermediates obtained at different stages of CuInSe2 nanoparticles synthesis process were investigated in detail by powder X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The XRD patterns showed that the phase formation sequence was CuSe→CuInSe2. The XPS results indicated that the valences of Cu and Se in CuSe were +1 and −1, respectively. The chemical composition of the solid intermediates revealed the presence of the solid-state In–Se secondary phases in the synthesis process. However, no XRD signals or Raman signals of the solid-state In–Se secondary phase were observed. Based on the experimental results, the possible reaction pathway was proposed.

First-principles study of valence band offsets at ZnSnP2/CdS, ZnSnP2/ZnS, and related chalcopyrite/zincblende heterointerfaces

The valence band offsets of chalcopyrite ZnSnP2 (ZSP), CdSnP2 (CSP), CuInSe2 (CIS), and CuGaSe2 (CGS) against zincblende CdS and ZnS are obtained using first-principles calculations based on hybrid density functional theory. The ZSP-CSP (ZCSP) alloy is isostructural to the CIS-CGS (CIGS) alloy and is known for its potential usage in photovoltaic applications. Therefore, the band offsets with other semiconductors, such as CdS and ZnS, are important. The calculated valence band offsets are ∼1.0 eV for ZSP/CdS and CSP/CdS, ∼1.2 eV for ZSP/ZnS and CSP/ZnS, ∼1.2 eV for CIS/CdS and CGS/CdS, and ∼1.3 eV for CIS/ZnS and CGS/ZnS. The CdS/ZnS valence band offset is within 0.1 eV. Transitivity of natural valence band offsets in the investigated semiconductors holds within ∼0.1 eV, which is smaller than the error in band alignment of ∼0.2 eV when ionization potential differences are used. The ZSP-CSP and CIS-CGS systems have similar valence and conduction band positions, which is an important piece of information for band offset engineering in the development of photovoltaics using ZCSP alloys.

One-pot, rapid synthesis of chalcopyrite CuInSe2 nanoparticles for low-cost thin film solar cell

In this work, highly dispersed and near stoichiometric chalcopyrite CuInSe2 nanoparticles were successfully synthesized via a facile and rapid one-pot method. The effects of reaction temperature and reaction time on the crystal phase, morphology, element composition and the absorption spectrum of the as-synthesized CuInSe2 nanoparticles were investigated by x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and UV-Vis-IR spectrophotometer, respectively. The XRD patterns showed that the as-synthesized nanoparticles had pure chalcopyrite phase with the particle size in the range of 50–300nm confirmed by FE-SEM images. The Vis-IR absorption spectra showed strong absorption in the entire visible light to near-infrared region, the estimated band gap of the as-synthesized nanoparticles matched very well with that of the bulk CuInSe2 material. All results suggested that the as-synthesized CuInSe2 nanoparticles were good light absorber layer material for thin film solar cell.

ChemInform Abstract: Classification of Lattice Defects in the Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth‐Abundant Solar Cell Absorbers

AbstractReview: emphasis on recent theoretical studies; 137 refs.

Mass transport in CuInSe2 from first principles

The wide scatter in experimental results has not allowed drawing solid conclusions on self-diffusion in the chalcopyrite CuInSe2 (CIS). In this work, the defect-assisted mass transport mechanisms operating in CIS are clarified using first-principles calculations. We present how the stoichiometry of the material and temperature affect the dominant diffusion mechanisms. The most mobile species in CIS is shown to be copper, whose migration proceeds either via copper vacancies or interstitials. Both of these mass-mediating agents exist in the material abundantly and face rather low migration barriers (1.09 and 0.20 eV, respectively). Depending on chemical conditions, selenium mass transport relies either solely on selenium dumbbells, which diffuse with a barrier of 0.24 eV, or also on selenium vacancies whose diffusion is hindered by a migration barrier of 2.19 eV. Surprisingly, indium plays no role in long-range mass transport in CIS; instead, indium vacancies and interstitials participate in mechanisms that promote the formation of antisites on the cation sublattice. Our results help to understand how compositional inhomogeneities arise in CIS.

Direct observation of the electrocrystallization of compound CuInSe2 during the early stages of deposition

Fundamental understanding of the early stages of electrocrystallization proceeding to a compound material deposition is of great importance. In this study, the growth mechanism of chalcopyrite CuInSe2, which is widely applied to thin film solar cells, was investigated. The electrodeposition was performed directly on carbon-coated nickel TEM grids so that the evolution of electrocrystallization can be truly followed using TEM. High-angle annular dark-field scanning transmission electron microscopy (HAADF–STEM) reveals that nanocrystalline cubic structure Cu2−xSe is deposited within the first 4ms. After 48ms, as Cu2+ and H2SeO3 around Cu2−xSe nuclei become depleted, In3+ is then reduced and the tetragonal CuInSe2 nanocrystals start to deposit around the Cu2−xSe nuclei surface to form core–shell structures. The formation of core–shell structures containing two semiconductor materials provides an insight for electrodeposition of compound semiconductors and the composition adjustment for electrodeposited CuInSe2.

Classification of Lattice Defects in the Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth‐Abundant Solar Cell Absorbers

The kesterite-structured semiconductors Cu2ZnSnS4 and Cu2ZnSnSe4 are drawing considerable attention recently as the active layers in earth-abundant low-cost thin-film solar cells. The additional number of elements in these quaternary compounds, relative to binary and ternary semiconductors, results in increased flexibility in the material properties. Conversely, a large variety of intrinsic lattice defects can also be formed, which have important influence on their optical and electrical properties, and hence their photovoltaic performance. Experimental identification of these defects is currently limited due to poor sample quality. Here recent theoretical research on defect formation and ionization in kesterite materials is reviewed based on new systematic calculations, and compared with the better studied chalcopyrite materials CuGaSe2 and CuInSe2 . Four features are revealed and highlighted: (i) the strong phase-competition between the kesterites and the coexisting secondary compounds; (ii) the intrinsic p-type conductivity determined by the high population of acceptor CuZn antisites and Cu vacancies, and their dependence on the Cu/(Zn+Sn) and Zn/Sn ratio; (iii) the role of charge-compensated defect clusters such as [2CuZn +SnZn ], [VCu +ZnCu ] and [ZnSn +2ZnCu ] and their contribution to non-stoichiometry; (iv) the electron-trapping effect of the abundant [2CuZn +SnZn ] clusters, especially in Cu2ZnSnS4. The calculated properties explain the experimental observation that Cu poor and Zn rich conditions (Cu/(Zn+Sn) ≈ 0.8 and Zn/Sn ≈ 1.2) result in the highest solar cell efficiency, as well as suggesting an efficiency limitation in Cu2ZnSn(S,Se)4 cells when the S composition is high.