CuIn0.7Ga0.3Se2 Research Articles

Structural, Optical and Electrical Properties of CuIn0.7Ga0.3Se2 Ingot Prepared by Direct Melting

CuIn0.7Ga0.3Se2 (CIGS) ingots were prepared by reaction of high-purity elements in stoichiometric proportions. The direct melting of elements was carried out using an original and low-cost process. The structural and morphological properties of the obtained material were investigated through x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. To detect and identify the defect chemistry of the obtained crystal, we used cathodoluminescence measurements at different temperatures. Moreover, the electrical properties of the CIGS material have been deeply investigated in this work using impedance spectroscopy. The activation energy for the conduction process was estimated. The conductivity data were found to obey the universal law of Jonsher. AC conduction is attributed to the correlated barrier hopping model. In the Nyquist diagram, two microscopic contributions to the electrical conduction were well identified.

Photoelectrochemical Properties of Particulate CuGaSe2 and CuIn0.7Ga0.3Se2 Photocathodes in Nonaqueous Electrolyte

Abstract The photoelectrochemical (PEC) properties of particulate CuGaSe2 (CGSe) and CuIn0.7Ga0.3Se2 (CIGS) photocathodes were evaluated in an acetonitrile electrolyte containing iron(III) acetylacetonate (Fe(acac)3) under simulated sunlight illumination, and compared to that in a typical aqueous electrolyte. The particulate CGSe and CIGS photocathodes can generate higher photovoltages, which is a more positive onset potential than the hydrogen evolution in an aqueous electrolyte possibly due to the facile one-electron reduction of Fe(acac)3, while the cathodic photocurrent decreased due to light shielding by the colored nonaqueous electrolyte. Indeed, the incident-photon-to-current conversion efficiencies (IPCEs) of the photocathode evidently decreased in the wavelength region of 400–600 nm, where the Fe(acac)3 acetonitrile electrolyte shows an intense light absorption. The CIGS photocathode generates a higher cathodic photocurrent than the CGSe during hydrogen evolution from the aqueous electrolyte, while the CGSe exhibits superior PEC performances to CIGS in the nonaqueous electrolyte, which can be explained by the energy level of the conduction band minimum (CBM) of CGSe and CIGS compared to the reduction potential for Fe(acac)3. Finally, the two-electrode PEC-voltaic (PECV) cell consisting of the CGSe photocathode and Pt anode demonstrated a stable generated photovoltage by a one-step photoexcitation process.

CuIn0.7Ga0.3Se2 thin films\u2019 properties grown by close-spaced vapor transport technique for second-generation solar cells

In this paper, CuIn0.7Ga0.3Se2 (CIGS) thin films are deposited on both glass (SLG) and glass/SnO2:F (SLG/FTO) substrates, by close-spaced vapor transport technique. The Hall effect measurements are performed in the temperature range (300–438 K) for the two SLG/CIGS samples namely CIGS1 and CIGS2, grown at substrate temperature (Ts) of 470 °C and 510 °C, respectively, to investigate the temperature effect on the electrical parameters such as hole concentration (p), conductivity (σ) and mobility (µ). As results, from Arrhenius diagram of (p) and (σ), bandgap energy (Eg) of about 1.38 eV and 1.24 eV are extracted for CIGS1 and CIGS2, respectively. Besides, activation energies (Ea) at 563.9 meV and 239.4 meV are determined for CIGS1 whereas values at 584.2 meV and 72.7 meV are obtained for CIGS2. Furthermore, average mobilities of 1.83 cm2/V s and 1.77 cm2/V s are achieved for CIGS1 and CIGS2 thin films, respectively. Pure aluminum (Al) Schottky contacts are deposited on the front side of FTO/CIGS thin film-devices by physical vapor deposition. Current–voltage (I–V) characteristics are measured and used to extract the electrical parameters of FTO/CIGS/Al Schottky diode using the one diode model. The electrical parameters including series resistance (Rs) of about 93.7 Ω and an ideality factor (n) around 3.47 indicate that the generation–recombination mechanism is predominant.

Characterization of CuIn0.7Ga0.3Se2 Thin Films Deposited by Single Stage Thermal Evaporation Process

Single phase CuIn0.7Ga0.3Se2 (CIGS) thin films are successfully deposited on glass substrates via a single stage thermal evaporation from a stoichiometric powder of CIGS. X‐ray photoelectron spectroscopy measurements reveal the existence of Cu‐ and Ga‐rich surface of the as‐grown CIGS thin films. The post‐growth annealing process lead to migration of the metallic atoms from the surface region into the bulk during the crystallization process, which subsequently causes a significant reduction in the reflection and a change in the mechanism of conduction. From the photoconductivity measurements it was deduced that the deposited CIGS films demonstrated a drastic decrease in resistivity under different illumination intensities. The post‐growth annealing effect on the morphology and structure of CIGS thin films is investigated by means of the atomic force microscopy and X‐ray diffraction measurements, respectively. Results show that there is a significant change in surface roughness as well as in degree of crystallinity of the films following the annealing process at different temperatures.

Different ligand exchange solvents effect on the densification of CuIn0.7Ga0.3Se2 prepared using the heating-up method

The effects of different ligand exchange solvents and heat treatment conditions on the densification and microstructure development of CuIn0.7Ga0.3Se2 (CIGS) crystallites synthesized using the heating-up method were studied in this work. The heat treatment effects on the organic molecules and crystalline structure were investigated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that oleylamine (OLA) adsorbed onto the CIGS surface was difficult to remove during sintering. Ligand-exchange with m-xylene or 1-hexanethiol can promote the removal of oleylamine adsorbed onto the CIGS surface and prevent the residual carbon from forming during sintering, which leads to grain growth and densification. A dense CuIn0.7Ga0.3Se2 can be obtained using the precursor powders after ligand-exchange with 1-hexanethiol and m-xylene to remove organic molecules and sintering at 600°C for 2h under Se atmosphere.

Correlation Between Microstructure and Optical Properties of Cu (In0.7, Ga0.3) Se2 Grown by Electrodeposition Technique

Polycrystalline thin films Cu (In0.7, Ga0.3) Se2 (CIGSe) were grown on copper foils at various cathodic potentials by using an electrodeposition technique. Scanning electron microscopy showed that the average diameter of CIGSe grains increase from 0.1 μm to 1 μm when the cathodic potential decreases. The structure and surface morphology were investigated by x-ray diffraction and atomic force microscopy (AFM) techniques. This structure study shows that the thin films were well crystallized in a chalcopyrite structure without unwanted secondary phases with a preferred orientation along (112) plane. Energy-dispersive x-ray analyses confirms the existence of CIGSe single phase on a copper substrate. AFM analysis indicated that the root mean square roughness decreases from 64.28 to 27.42 when the potential deposition increases from −0.95 V to −0.77 V. Using Raman scattering spectroscopy, the A1 optical phonon mode was observed in 173 cm−1 and two other weak peaks were detected at 214 cm−1 and 225 cm−1 associated with the B2 and E modes of the CIGSe phase. Through spectroscopy ellipsometry analysis, a three-layer optical model was exploited to derive the optical properties and layer thickness of the CIGSe film by least-squares fitting the measured variation in polarization light versus the obtained microstructure.

Structure and Optical Properties of Cu (In0.7, Ga0.3) Se2 Absorbers on Copper Substrate for Photovoltaic Solar Cells Application

Polycrystalline thin films Cu (In0.7, Ga0.3) Se2 (CIGSe) were grown on copper foils at various cathodic potentials by using electrodeposition technique. Scanning electron microscopy (SEM) displays that average diameter of CIGSe grain increases from 0.1μm to 1μm when cathodic potential decreases. The structure and surface morphology were investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. This structure study shows that the thin films were well crystallized in chalcopyrite structure without unwanted secondary phase with preferred orientation along (112) plane. Energy-dispersive x-ray analysis (EDAX) confirms the existence of CIGSe single phase on copper substrate. AFM analysis indicated that the root mean square (RMS) roughness decreases from 64.2 to 27.4 when the potential deposition increases from −0.95V to −0.77V. Using Raman scattering spectroscopy, the A1 optical phonon mode was observed in 173cm−1 and two other weak peaks detected at 214cm−1 and 225cm−1 associated to the B2 and E modes of the CIGSe phase. Through spectroscopy ellipsometry (SE) analysis, three layer optical model was exploited to derive the optical properties and layer thickness of the CIGSe film by least-squares fitting the measured variation in polarization light versus the obtained microstructure.

Deposition and Characterization of CIGS Thin Films Deposited by Chemical Spray Process

CuIn0.7Ga0.3Se2 (CIGS) thin films were successfully deposited by chemical spray method under air environment and then the as-deposited films were annealed in a furnace. In order to study the influence of annealing temperature and condition on the properties of the CIGS films, annealing temperature was varied from 200°C to 500°C under nitrogen as well as in selenization conditions. The annealing temperatures and conditions exerted an effect on the properties of the prepared thin films. Based on the XRD measurements, the optimum annealing condition to synthesize the CIGS thin films was 500°C under both conditions. The crystalline structure of the film annealed at 500°C was in good agreement with the tetragonal structure in the reference. The surface morphology of the thin film under selenization condition was smooth, dense with lager grain size. XRD, SEM, UV-vis, XPS and ICP-AES were employed to study the influence of annealing temperature on the physical properties of the films.

CIGS absorber preparation by non-vacuum particle-based screen printing and RTA densification

CuIn0.7Ga0.3Se2 (CIGS) thin-films are prepared by the particle-based screen printing technique followed by rapid thermal annealing (RTA) densification. Due to the short RTA time, CIGS absorber remains the ideal stoichiometric ratio originated from the CIGS particles in the coating paste and thus the conventional selenization process is not required. The effects of the particle concentrations of the coating paste, the RTA temperature and normal loading during RTA on the performances of the CIGS thin-films are studied. The film thickness increases with the increase of the particle concentration of the coating paste. The carbon content of the film is nearly zero when the RTA temperature is greater than 650°C. The carrier concentration and Hall mobility of the CIGS film increase when increasing the RTA temperature from 300°C to 650°C. Using the coating paste with a particle concentration of 40wt% for screen printing and a three-step, 250°C solvent removal for 5min, 500°C annealing for 7min and 650°C densification for 3min, 1.97Ncm−2 normal loading RTA process, a p-type chalcopyrite CIGS film with the carrier concentration of 1.23×1015cm−3 and mobility of 26.21cm2V−1s−1 is obtained.

Highly efficient flexible CuIn0.7Ga0.3Se2 solar cells with a thick Na/Mo layer deposited directly on stainless steel

Bi-layered back contact structures consisting of Mo-capping and Na-doped Mo layers have been investigated for the purpose of providing extra Na for CuIn0.7Ga0.3Se2 (CIGS) absorbers for high efficiency solar cells on a stainless steel substrate. This approach utilizing a thick back contact layer does not require a buffer layer on the substrate. The cell performance depends largely on the content of Na in the Mo:Na layer as Na easily diffuses into the absorber layer. The best cell efficiency of 15.04% is obtained for the cell incorporating the 600nm Mo-capping and 900nm 10% Na-incorporating Mo layers. This enhancement is attributed mainly due to the substantial increase of Voc as a result of higher carrier concentration and lower leakage current of the extra Na-involved absorber.

Preparation and Characterization of Hot Wall Deposited CuInGaSe<sub>2</sub> Thin Films for Solar Cell Applications

CuIn0.7Ga0.3Se2 (CIGS) bulk compound was prepared by direct reaction of high purity (99.99%) elemental copper, indium, gallium and selenium. Using the prepared bulk CIGS, polycrystalline CuInGaSe2 thin films were deposited onto well cleaned soda-lime glass substrates using hot wall deposition technique by optimizing process parameters such as the wall temperature, filament current and time of deposition. The x-ray diffraction studies on the as-prepared films revealed polycrystalline nature. The composition of the chemical constituents present in the prepared bulk and thin films has been determined using energy dispersive X-ray analysis (EDX). The surface morphology of CIGS thin film of deposition time 3 min. have been carried out using Atomic Force Microscopy (AFM). The AFM images revealed that the average grain size was 20 nm and the surface roughness was about 8 nm. Transmittance spectra in the wavelength range of 190 nm to 2500 nm was obtained using a double beam spectrophotometer (UV-VIS) and the results are discussed.

Study on the CIGS Thin Film Formation by Modified Spray Process

The highly uniform polycrystalline CuIn0.7Ga0.3Se2 (CIGS) thin films for solar cell application were successfully synthesized on the glass substrates using a modified spray process and a continuous flow micro-reactor (CFM) process at low temperature. The as-deposited thin films prepared by each method were annealed under vacuum condition without additional selenization. In order to study the influence of annealing temperature on the properties of the CIGS films, annealing temperature were varied from 200°C to 400°C. The annealing temperature exerted an effect on the properties of the prepared thin films. Based on the XRD measurements, the optimum annealing condition to synthesize the CIGS thin films was 200°C. The crystalline structure of the film annealed at 200°C was in good agreement with the tetragonal structure in the reference. CuIn0.7Ga0.3Se2 thin films were also deposited by a solution-based CFM method and were then thermally treated under the same conditions as the spray. They were compared with the properties of the films deposited by the spray in order to figure out which deposition method is more effective for the synthesis of the CIGS thin films. XRD, SEM, UV-vis, and XPS were employed to study the influence of annealing temperature on the physical properties of the films.

Controlling morphology and crystallite size of Cu(In0.7Ga0.3)Se2 nano-crystals synthesized using a heating-up method

CuIn0.7Ga0.3Se2(CIGS) nano-crystals were successfully synthesized via a heating-up process. The non-coordinating solvent (1-octadecene) and selenium/cations ratio effects on the crystalline phase and crystallite size of CIGS nano-crystallites were investigated. It was observed that the CIGS nano-crystallite morphology changed from sheet into spherical shape as the amount of 1-octadecene addition was increased. CIGS nano-crystals were obtained in 9–20nm sizes as the selenium/cations ratio increased. These results suggest that the monomer reactivity in the solution can be adjusted by changing the solvent type and selenium/cations ratio, hence affecting the crystallite size and distribution.

Annealing Effect on the Properties of Cu(In0.7Ga0.3)Se2 Thin Films Grown by Femtosecond Pulsed Laser Deposition

This work reports the crystallization, microstructure, and surface composition of CuIn0.7Ga0.3Se2 (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X‐ray diffraction, Raman scattering, UV‐visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuSe initially formed on the as‐deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as‐deposited and annealed films as demonstrated by preliminary tests.

Characterization of high quality Cu(In,Ga)Se2 thin films prepared by rf‐magnetron sputtering

AbstractThis paper reports the production of high quality polycrystalline thin layers of CuIn0.7Ga0.3Se2 (CIGS), using rf‐magnetron sputtering, from a powder target. These films are designed to be used as absorbers in solar cells. The depositions were carried out at substrate temperatures below 250 °C and glass substrates was used. The influence of the substrate temperatures on the crystalline quality as well as structural, optical and electrical properties of thin layers obtained has been studied. X‐ray diffraction showed that the films were highly orientated in the (112) and/or (204)/(220) direction. In2Se3 secondary phase was observed on the samples grown at lower substrate temperatures. The surface morphology of CIGS layers studied by Atomic Force Microscopy (AFM) and Scanning Electronic Microscopy (SEM) has been also discussed. The most surprising and exciting outcome of this study was that the as grown films were of near stoichiometric composition. Resistivity measurements were carried out using the four point probe method. The optical absorption showed that energy gap values are between 1.13 and 1.18 eV and rather sharp absorption fronts. Thin film resistivities are between 10.7 and 60.9 Ω.cm depending on the experimental growth conditions (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation Mechanisms of Cu(In0.7Ga0.3)Se2 Nanocrystallites Synthesized Using Hot‐Injection and Heating‐Up Processes

Nearly monodispersed CuIn0.7Ga0.3Se2 (CIGS) nanocrystals were successfully prepared using the thermal decomposition of copper, indium (In), gallium (Ga), and selenium–oleylamine (OLA) complexes via the heating‐up process. The phase formation sequence was CuSe→CuInSe2→CIGS. The CIGS nanocrystals synthesized using the heating‐up process exhibited a single chalcopyrite phase and its chemical composition was close to stoichiometric. However, phase separation of the In‐rich and Ga‐rich phases was found using the hot‐injection method due to the difference in reactivity between In–OLA and Ga–OLA complexes.