CIS Films Research Articles

Experimental and theoretical study of electrodeposited CuInS2 thin films for solar cell applications

Absorbent CuInS2 layers were successfully prepared using an electrodeposition technique on ITO-coated glass, followed by a sulfidation process. The effects of sulfurization time on the structural, morphological and optical properties of samples were examined. The structure, morphology, and composition of synthesized films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), while the optical properties were examined by UV-VIS-NIR spectrophotometry. The experimental results show that the resulting films (CIS) are polycrystalline with a chalcopyrite structure with a preferential orientation along the (112) plane and show that Cu atoms separate near the grain boundaries and a wide bandgap value of 1.52 eV. The SEM study showed that the surface of the CIS films was dense and uniform. Theoretical calculations carried out by TB-mBJ showed a wide bandgap of 1.15 eV, a high refractive index, and absorption coefficient in the visible region which is consistent with the experimental results found.

Photo-electrochemical performance of CIS and CIGS solar thin films arranged through a novel CISe/Ga-Se bilayer electrodeposition

In current work, we focused on the electrodeposition of CuInSe2 and CuIn1-xGaxSe2 by a unique two-step deposition method. Initially by a single step technique, CuInSe2 thin film was electrodeposited using an electrolyte comprised of citric acid-SDS. Further, the gallium selenium thin film was deposited on FTO substrate by potentiostatic method in tartaric electrolyte bath to get a bilayer of Ga-Se upon CISe thin film. For improving the adhesion and smoothness of electrolyth bath, sodium dodecyle sulfate has been added and it is also eliminating multinuclear growth. The CISe and CIGSe samples were further annealed at 300 0C and 525 0C in nitrogen atmosphere respectively. The structural, compositional, optical and electronic representation of as electrodeposited and annealed thin films of CISe and CIGSe were investigated by XRD, SEM and electrochemical analysis. The thin film of as electrodeposited and annealed CIS and CIGS exhibited a p-type behavior as confirmed by with photoelectrochemical (PEC) properties and by Mott-Schottky (M−S) test. By the slope and intercept values of the M−S plot, the carrier concentration and flat band values were determined. The calculated carrier concentration of as deposited and annealed CISe and CIGSe thin films are 3.70 × 1023 cm−3, 1.51 × 1024 cm−3, 9.60 × 1021 cm−3 and 7.79 × 1023 cm−3 respectively. The calculated flat band potential of as electrodeposited and annealed CISe and CIGSe thin films are 115 mV,85.48 mV, 332 mV and 58.65 mV. Here also we have done the Electrochemical Impedance Studies (EIS). The EIS were performed for as-electrodeposited and annealed CIS and CIGS thin films in the electrolyte solution to understand the charge transfer mechanism. The observed Rct values 1397 and 178.4 Ω cm2 for as-deposited and annealed CIS film and Rct values 158.2 and 81.27 Ω cm2 for as-electrodeposited and annealed CIGS thin films respectively. At a potential of −0.4 V/SCE, the obtained photocurrent density for as deposited and annealed CISe and CIGSe thin films by PEC test are 1.10 × 10−4 A cm−2, 1.35 × 10−4 A cm−2, 1.07 × 10−4 A cm−2 and 3.01 × 10−4 A cm−2 respectively.

Self-aggregation, H-bonding, and photoresponse in film and solution states of azobenzene containing polyurea.

We critically understand the hydrogen bonding interactions and electronic transitions occurring in a thin film as well as in solution of a photo-responsive polymer, azo-polyurea (azo-PU). We synthesize azo-PU by covalent attachment of the azobenzene chromophore to the main chain of polyurea. Azo-PU shows reversible photoisomerization between trans and cis states upon light exposure, the occurrence of which is typically analysed using the π-π* and n-π* electronic transition peaks in the UV-visible absorption spectrum. We find that the π-π* and n-π* bands undergo a redshift and blueshift respectively on dissolving azo-PU in DMF solvent, resulting in a single overlapped peak in the spectrum. However, upon UV irradiation, these bands split into two independent transitions that are characteristic of azo-PU solid films. These observations are explained based on the changes in polymer-polymer and polymer-solvent interactions through hydrogen bonding and self-aggregation tendency. The experimental findings are corroborated using DFT simulations which provide useful insights into electronic orbital transitions, electron distribution, and hydrogen bonding interaction through IR vibrational modes.

The influence of Ag doping and annealing on phase, structural and carrier transport characteristics of CIS thin films

Abstracts The un-doped and Ag-CIS thin films were deposited on quartz glass substrates by single source thermal evaporation method. Then, some CIS films were annealed in vacuum or N2 atmosphere from 350 °C to 550 °C. The results of XRD patterns showed the phase compositions of CIS thin films were changed with the increase of annealing temperature. Meanwhile, the results of Raman measurement confirmed a dramatic transition from CA phase to CH phase. Furthermore, the Ag atoms could promote the recrystallization process and the transition from CA phase to CH phase, which might result in the improvement of optical-electrical properties of CIS film. The transient photocurrent of the CIS-3 sample annealed at 450 °C was higher than those of other samples, which might be related to the good crystal quality. The results of I-V curves confirmed the N-type conduction of CIS-3 films, which was consistent with the results of EDS measurement. The C-V results of CIS-2 films also were the same as the results of EDS measurement. Furthermore, for the CIS-2 samples, with increase of annealing temperature, the change of conduction type may be related to the S element volatilization under vacuum situation and the decomposition of the substitutional defects AgIn.

Identification of Defect Levels in Copper Indium Diselenide (CuInSe2) Thin Films via Photoluminescence Studies

Photoluminescence (PL) spectroscopy has been used to study the defect levels in thin film copper indium diselenide (CuInSe2, CIS) which we are developing as the absorber layer for the bottom cell of a monolithically grown perovskite/CuInSe2 tandem solar cell. Temperature and laser power dependent PL measurements of thin film CIS for two different Cu/In ratios (0.66 and 0.80) have been performed. The CIS film with Cu/In = 0.80 shows a prominent donor-to-acceptor peak (DAP) involving a shallow acceptor of binding energy ∼22 meV, with phonon replica at ∼32 meV spacing. In contrast, PL measurement of CIS film for Cu/In = 0.66 taken at 20 K exhibited an asymmetric and broad PL spectrum with peaks at 0.845 eV and 0.787 eV. Laser intensity dependent PL revealed that the observed peaks 0.845 eV and 0.787 eV shift towards higher energy (aka j-shift) at ∼11.7 meV/decade and ∼ 8 meV/decade with increase in laser intensity respectively. The asymmetric and broad spectrum together with large j-shift suggests that the observed peaks at 0.845 eV and 0.787 eV were related to band-to-tail (BT) and band-to-impurity (BI) transition, respectively. Such a band-tail-related transition originates from the potential fluctuation of defect states at low temperature. The appearance of band related transition in CIS film with Cu/In = 0.66 is the indicator of the presence of large number of charged defect states.

Annealing study of electrodeposited CuInSe2 and CuInS2 thin films

In this study CuInSe2 and CuInS2 thin films were prepared onto ITO glass substrate using the electrodeposition technique in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis. The annealing effects on electrodeposited precursors were investigated. The chalcopyrite structure of CuInSe2/CuInS2 showed an enhancement of crystallinity after subsequent selenization/sulfurization treatment in Se/S atmosphere, respectively. XRD and SEM studies revealed a dramatic improvement of the crystalline quality of CIS films after annealing treatments. Mott–Schottky measurements were used to assess the conductivity type of the films and their carrier concentration. The prepared samples underwent an etching process to remove the binary accumulated Cu2−x(Se,S) phases shown in FESEM pictures. This etching process has shown a noticeable decrease in both, the flat band potential, Vfb (V), and the number of acceptors, NA (cm−3) in selenized CuInSe2 and sulfurized CuInS2 samples.

Physical properties of highly crystalline CIS layer prepared using single phase electrodeposition and low temperature RTP annealing

CuInSe2 nanoparticles (CIS-NP) were synthesized on ITO-coated glass substrate by electrodeposition and rapid thermal processing (RTP). The as-deposited films were annealed under argon atmosphere at 250 °C, 350 °C and 450 °C using RTP during a short annealing time. The latter is practicable to avoid further losing of the Se content in CIS films. In order to analyze the effect of annealing temperature, the structural, morphological, optical and electrical properties were investigated by means of X-ray diffraction, scanning electron microscopy, UV–Visible Spectroscopy and Mott-Schottky plots respectively. XRD results show that elaborated films have a tetragonal chalcopyrite CIS with preferential orientation along the (112) orientation. The phase formation of CIS-NP with good crystallinity was observed at low annealing temperature. Optical absorption studies indicate a direct band gap around 1.02 eV at 250 °C. The optical constants such as refractive index n(λ) and extinction coefficient k(λ) were estimated using an appropriate optical model. To determine the doping type of elaborated semiconductor, its flat band potential and the free carrier concentration we used the Mott-Schottky plots. A new attempt to anneal the electrodeposited CIS films by short annealing duration using RTP process was proved to be a useful method to synthesize polycrystalline CIS films for solar cell application.

CIS, CIGS and CIBS thin film solar cells and possibilities of their application in BIPV

CIS, CIGS and CIBS thin film solar cells and possibilities of their application in BIPV

Preparation of perfect chalcopyrite ordering CuInS2 thin films by high-temperature sulfurization of metal oxide nanoparticles

In this letter, a low-cost non-vacuum process is introduced to fabricate the pure crystalline chalcopyrite (CH) CuInS2 thin films. Since the Chalcopyrite (CH) and CuAu (CA) ordering phases have very close formation energy and structures and tend to coexist in CIS films, it is very difficult to get single-phase chalcopyrite CIS in normal way. Simply, in this study, the high-temperature sulfurization of copper indium oxide nanoparticles precursor layers has been taken out and the presence of the metastable CuAu (CA) ordering phase is successfully avoided in the chalcopyrite CIS thin films. In addition, films sulfurized at high temperature show pure chalcopyrite phase, good crystallization and reliable optical properties, which are suitable for preparation of high efficiency solar cells.

Effect of the Replacement of Some Indium Atoms with Aluminum Atoms on the Behaviour of p-CuInSe2 Thin Films and Schottky Diodes

As environmental and energy resource concerns have increased, greater stress has been placed on the development of renewable energy resources such as photovoltaic electric generators. Chalcopyrite semiconductors have gained prominence as solar cell fabrication materials due to its steady progress in conversion efficiencies. These have emerged as leading absorber semiconducting material for solar power generation purposes. CulnSe2 (CIS), a prominent member of the chalcopyrite family, has emerged as a promising material for high efficiency thin film solar cells. Due to its favorable electrical and optical properties, stability and inexpensive means of production that several recent advances have been made to improve its bandgap [Eg]. The bandgap of CIS has been tailored to match the desired portion of the Solar Spectrum by alloying the group III (Ga and Al) or group VI (S and Se) elements. An extensive research work has been carried out on Cu(In,Ga)Se2 [CIGS] and CuIn(S,Se)2 [CISS] alloy systems but the efficiency of these devices with Eg >1.3 eV is reduced due to degradation of the electronic properties of the absorber layer leading to losses in the fill-factor and the open-circuit voltage. The performance of thin film CIS based solar cells has alternatively been improved by the addition of Al in place of Ga to form CuInAlSe2(CIAS) absorber layers with changed bandgap to match the selective regions of the solar spectrum. Further, Ga is scarce and expensive material and can preferably be replaced by inexpensive and abundant Al. In the present investigation, behaviour of thin film CIAS to that of CIS as an absorber layer portion of the solar cells has been studied. Both the materials possessed tetragonal structure and found oriented towards < 112 > set of planes. The addition of ‘Al’ to CIS films caused reduction in the lattice imperfections’ which resulted in the improved cystallinity of the films. The grain size increased while microstrain and dislocation density decreased in CIAS. The films demonstrated decrease in the cohesive force between film and the substrate material. The optical analysis of the films revealed that the bandgaps and absorption coefficients increased on Al substitution and, thus, CIAS films have been found to be more suitable as an absorber layer in solar cells. The electrical measurements of the films showed that both CIS and CIAS films possessed p-type conductivity. Further, a significant improvement has been observed in the conductivity as well as mobility values in the CIAS films. The phenomenon has been attributed due to the reduction in the grain boundary scattering in the CIAS in comparison to CIS films. The Schottky Diodes of both the types of films were formed using Aluminum metals. The reverse biased leakage currents measured from the I-V/C-V characteristics of CIS were found to lower than that of CIAS films. The forward biased parameters such as ideality factors and series resistance decreased while barrier heights increased in the Al/p-CuIn0.81Al0.19Se2 Schottky Diodes. Further, the temperature dependence of the I-V/C-V characteristics of the undertaken CIAS diodes has been explained on the basis of barrier inhomogenities existing over the M-S interface. However, some deviations have been observed between the data generated on the basis of Gaussian Distribution Function for barrier inhomogenities to that obtained from the experimental studies of undertaken Schottky Diodes which indicated the existence of current component due to tunneling alongwith the thermionic emission of the charge carriers existing over the M-S interface.

Improving the efficiency of a poly(3-hexylthiophene)-CuInS2 photovoltaic device by incorporating graphene nanopowder

In the present work, the effect of incorporation of graphene on the poly(3-hexylthiophene) (P3HT):CuInS 2 quantum dot (CIS QD)-based solar cell has been studied. For this purpose, the concentration of graphene is varied from 0 to 0.01% w/w in P3HT–CIS (1:0.5) film. It is found that graphene does not deteriorate the absorption of the composite film. It assists in dissociating the photogenerated excitons (both in P3HT and QDs) owing to its two-dimensional structure and high electron affinity as is evident by photoluminescence (PL) quenching. At 0.01% w/w concentration of graphene about ∼95% of PL is quenched. The electrical characteristics show that the incorporation of graphene enhances the efficiency of the device by establishing interconnected conducting pathways in the volume of polymer matrix. The maximum efficiency is observed to be 1.5% at 0.005% w/w content of graphene. However, at higher concentration, i.e., 0.01% w/w, the device starts deteriorating.

CuInS2 nanostructures: Synthesis, characterization, formation mechanism and solar cell applications

This investigation reports the synthesis of CuInS2 nanostructures by using [Cu(gly)2] via a microwave-assisted method. CuInS2 nanostructures were obtained from a mixture of InCl3, [Cu(gly)2] and different sulfur sources in propylene glycol. In this work, the effect of different sulfur sources on the morphology of CuInS2 nanostructures was studied. CuInS2 nanostructures were characterized by XRD, SEM, TEM, EDS, and FT-IR. To fabricate a standard solar cell, CdS film was directly deposited on top of the CIS film prepared by Doctor's blade method through chemical bath deposition. The as-deposited CdS/CuInS2 film was used for the photovoltaic measurements.

Spray Pyrolysis of CuIn(S,Se)2 Thin Films Using Hydrazine-based Solutions

ABSTRACTA novel approach to fabricate CuIn(S,Se)2 (CIS) thin films through ultrasonically spraying a hydrazine-based precursor solution onto a heated substrate is reported. The effects of the composition of the precursor solutions and the deposition temperature on the CIS film properties were investigated by comparing thin films fabricated using aqueous metal salt solution, anhydrous hydrazine solution, and hydrazine hydrate solution at various deposition temperatures. Crystallite size and texture coefficient in the preferred (112) orientation in the sprayed films increased when the aqueous solution was replaced by hydrazine-based solutions. Additionally, the hydrazine-based precursor solutions resulted in films with better surface smoothness and compositional uniformity than those fabricated using water-based solutions and the hydrazine hydrate solution resulting in the smoothest, most uniform films. The sprayed films were used to fabricate preliminary solar cells that demonstrated a modest photovoltaic response. With optimization, the synthesis of high-quality CIS films by spray pyrolysis from a hydrazine hydrate solution could demonstrate the potential for a low-cost, high-throughput manufacturing process.

The Effect of Thickness on Optical Band Gap and N-type Conductivity of CuInS2 Thin Films Annealed in Air Atmosphere

Structural, electrical and optical properties of CuInS2 thin films of various thicknesses, grown on heated glass substrates at 100°C by thermal evaporation method were studied. These films were annealed in air atmosphere at temperature of 200°C. The thickness of the CIS films was varied from 436 to 80nm. It was found that the structural properties, FWHM and grain size degraded with decreasing its thickness. The peak intensity decreases with the film thickness and the X-ray spectra are polycrystalline in nature excluding films with thickness less than 111nm, the peak intensity disappears and films are amorphous in nature. However, with decreasing the film thickness from 436 to 111nm, the optical band (Eg) gap of CuInS2 material is in the range 1.42 to 1.81eV. Hot probe method showed that all the annealed CuInS2 samples exhibit n-type conductivity with low resistivity values in the range 3.60 to 0.08 kΩ.m. We suggests that the minimum thickness to obtain polycrystalline CuInS2 thin films is 111nm, the band gap energy of CuInS2 thin films can be controlled by varying the film thickness and the n-type conductivity can be obtained after annealing in air atmosphere.

Cyclic Voltammetry Study on Electrodeposition of CuInSe2 Thin Films

Chalcopyrite (CIS) is considered to be an effective light-absorbing material for thin film photovoltaic solar cells. CIS thin films have been electrodeposited onto Mo coated and ITO glass substrates in potentiostatic mode at room temperature. The deposition mechanism of CIS thin films has been studied using the cyclic voltammetry (CV) technique. A cyclic voltammetric study was performed in unitary Cu, In, and Se systems, binary Cu-Se and In-Se systems, and a ternary Cu-In-Se system. The reduction peaks of the ITO substrate were examined in separate , , and solutions. Electrodeposition experiments were conducted with varying deposition potentials and electrolyte bath conditions. The morphological and compositional properties of the CIS thin films were examined by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The surface morphology of as-deposited CIS films exhibits spherical and large-sized clusters. The deposition potential has a significant effect on the film morphology and/or grain size, such that the structure tended to grow according to the increase of the deposition potential. A CIS layer deposited at -0.6 V nearly approached the stoichiometric ratio of . The growth potential plays an important role in controlling the stoichiometry of CIS films.

The effect of thermal annealing of Mo film on the CuInSe2 layer texture and device performance

The influence of annealing treatment of molybdenum (Mo) film on the growth of CuInSe 2 (CIS) thin film has been studied. We show that Mo film is with much better electrical conductivity and adhesion after being annealed in vacuum. It is found that annealing of Mo film not only modifies the orientation of In 2 Se 3 (IS) precursor, but also the texture of CIS crystal. Thermally treated Mo film favors the growth of (220/204) oriented CIS film. CIS solar cell grown on annealed Mo film is found to be with higher device efficiency, which is attributed to the increased fill factor ( FF ). • After being annealed in vacuum, the electrical conductivity and mechanical stability of Mo film are much better. • Annealing of Mo film modifies the orientation of In 2 Se 3 precursor. • Annealing of Mo film modifies the orientation of CIS crystal. • We improve performance of the CuInSe 2 solar cell by annealing Mo film substrate.

Optical enhancement and selenisation models of CuInSe2 films by substrate choosing processes

In this research, substrate materials have been used for the production of the absorbed layer of salor cell–CuInSe2 films. The microstructures of CuInSe2 films have been studied through X-ray diffraction and scanning electron microscopy. Surface character and optical properties of CuInSe2 films have been investigated on the substrate materials [Si, Al, SnO2 doped F (SFO), Cu and steel]. The results show that CIS phase was changed from amorphous structure to single phase structure with the substrate changed from Si to Al, steel and Cu. It also found that only two-phase structures existed in the CIS films on SFO. Meanwhile, substrate processes were found to be a vital parameter in determining the selenisation mechanism and grain size of the CIS films. An inverse relation between the substrate materials and the optical properties of the CIS films was observed.

Band gap engineering of tandem structured CIGS compound absorption layer fabricated by sputtering and selenization

Band gap engineering was executed to fabricate a multi-junction stacked i.e. tandem Cu(In,Ga)Se2 (CIGS) absorption layer. The CIGS absorption layers consist of multi-junction stacked CIS/CIGS/CGS thin films from bottom to top with increasing band gap. Tandem CIGS layers were fabricated by using three precursor of CuIn, In/CuGa/In, and CuGa onto the Mo coated soda-lime glass (SLG) by the sequential sputtering of CuIn, CuGa, and In targets. The CIG precursors were converted into CIGS absorption thin film by selenization process. From the X-ray diffraction (XRD) pattern of CIS/CIGS/CGS tandem layer, with the prominent peak shift for (112) reflections was attributed to the individual CIS, CIGS, and CGS phases at 26.76°, 27.15°, and 27.65° diffraction angles, respectively. The morphologies and atomic (at%) composition uniformity onto the surface and along the depth were extensively analyzed with field effect scanning electron microscope (FESEM) attached energy dispersive spectroscopy (EDS) and secondary ion mass spectroscopy (SIMS). The optical properties such as transmittance, reflectance and absorbance were found to improve in the infrared region for all the tandem CIGS layers. Near the fundamental absorption edge, the absorption coefficient was approached to 105cm−1 for CIS/CIGS/CGS tandem layer. The straight-line behavior indicates that the films have a direct band gap. The band gap was found to increase from 1.15 to 1.74eV with the Ga-grading along the depth of individual CIS, CIGS, and CGS thin films. In the tandem CIGS layer, consist of CIS/CIGS, CIS/CGS, and CIS/CIGS/CGS thin films, the band gap was further increased from 1.42 to 2.06eV, respectively. Such band gap engineering in CIGS tandem absorption layer will be a stepping stone to further improve the solar cell performance.

Pulsed Electrodeposition of CuInSe2 Thin Films with Morphology for Solar Cell Applications

Copper indium diselenide (CuInSe2) films have been prepared by pulse electrodeposition technique on Molybdenum substrate followed by post-deposition annealing at 550°C. Optimization of pulse parameters by varying the pulse duration (duty cycle) in order to achieve high quality films has been reported. Appropriate manipulation of pulse parameters has resulted in a novel flake-like crystallite morphology and better control over the composition of individual elements. The CIS thin films were comprehensively characterized using SEM-EDS, FIB, XRD and UV-DRS to study their morphology, phase constitution, etc. and PEC (photoelectrochemistry) measurements were also carried out to ascertain the photoelectrochemical performance of the CIS absorber layer. The bandgap of the CIS films was determined to be 1.02 eV. The flake like crystallite morphology observed in CIS thin films under the optimized processing conditions was found to yield enhanced cathodic photoresponse under solar simulated light with a photocurrent density of 20 μA/cm2 (observed at a potential of −0.6 V vs. SCE). The films exhibited a photoresponse typical of a p-type semiconductor.

Electrodeposition of CIS films on the Mo back electrodes with different crystallinities

Electrodeposition of copper indium diselenide (CuInSe2), which is an absorption layer for thin film solar cells, has been studied on a molybdenum (Mo)-coated glass with different crystallinities. Metastable FCC Mo and BCC Mo coatings were prepared by R.F. sputtering with varying R.F. power (100–170W) and Ar pressure (3–11mTorr). Experimental results indicated that the Mo coating deposited at lower power and higher pressure had smaller crystallite size. Cross-sectional transmission electron microscopy showed that the Mo coating deficient in crystallinities contained micro voids residing in the boundaries of the columnar grains and had higher oxygen content, as measured by energy dispersive spectroscopy. The crystallinity of Mo coatings strongly influenced the open circuit potential in the electrolyte for CIS electrodeposition. Consequently, the Cu/In ratio of CIS deposits plated at a constant potential (−0.7 vs. SCE) varied with the distinct Mo coatings. Moreover, the CIS deposit on the various Mo-coated glasses displayed a different morphology. The effect of the crystallinity of Mo coatings on hydrogen evolution reaction at pH 1.55 was also explored. Hydrogen evolution during the CIS electrodeposition may be one of the key factors to influence the CIS morphology. How the crystallinity of the Mo coating affects the composition and morphology of the CIS deposits can be useful for device fabrication and deserves for further study.