CuInSe2 Thin Films Research Articles

CuInSe2-Based Near-Infrared Photodetector

Near-infrared (NIR) photodetectors have interesting roles in optical fiber communications and biomedical applications. Conventional NIR photodetectors have been realized using InGaAs and Ge, of which the cut-off wavelengths exceed 1500 nm. Si-based photodetectors exhibit limited external quantum efficiency at wavelengths longer than 1000 nm. By synthesizing a CuInSe2 compound on a glass substrate, photodetectors that can detect optical wavelengths longer than 1100 nm have been realized in this study. The bandgap energies of the CuInSe2 thin films were tuned by varying the Cu/In ratio from 1.02 to 0.87. The longest cut-off wavelength (1309 nm) was obtained from a CuInSe2 thin film having a Cu/In ratio of 0.87. The responsivity of the photodiode was measured under the illumination of a 1064 nm laser light. The photo responses exhibited linear response up to 2.33 mW optical illumination and a responsivity of 0.60 A/W at −0.4 V.

Impact of selenization temperature on the performance of sequentially evaporated CuInSe2 thin film solar cells

In the present work, modified stacking of sequentially evaporated metallic precursors and two-step selenization was performed to examine the photovoltaic quality of the copper indium diselenide (CISe) thin films. The photovoltaic device performance as a function of selenization temperatures was investigated. Structural analysis showed that the chalcopyrite CISe thin films' crystallinity steadily improved as selenization temperatures increased from 450 to 550 °C. The grain size of the CISe thin films increased up to 1.0 μm with increasing selenization temperatures. The optical band gap energy fluctuated between 0.99 and 1.02 eV depending upon selenization temperatures. The uniform distribution of elements in the films' depth profile was investigated from secondary ion mass spectroscopy (SIMS). Open circuit voltage (Voc) increased from 258 to 543 mV upon increasing the selenization temperature due to enhanced crystal quality and concentration of sodium diffused through the soda-lime glass (SLG) substrate. A fabricated CISe solar cell attained 9.37% of best conversion efficiency at 550 °C of selenization temperature. These results demonstrate the selenization of evaporated metallic precursors at room temperature to synthesize good quality CISe based absorbers, which substantiate the viability of the proposed approach to obtain solar cells with high efficiency.

Over 15% efficient wide-band-gap Cu(In,Ga)S2 solar cell: Suppressing bulk and interface recombination through composition engineering

Over 15% efficient wide-band-gap Cu(In,Ga)S2 solar cell: Suppressing bulk and interface recombination through composition engineering

Influence of complexing agents-aided CuInSe2 thin films by single-step electrochemical deposition and photoelectrochemical studies

CuInSe2 thin films were deposited on ITO glass substrate by one-step electrochemical deposition (ECD) method without and with complexing agents like tetramethyl ammonium hydroxide (TMAH) and triethanolamine (TEA) at different temperatures. X-ray diffraction (XRD) studies confirm the as-deposited CuInSe2 thin films at 85 °C without and with complexing agents belong to the tetragonal crystal structure with the dominant peak representing the (112) plane. The single crystallized CuInSe2 thin films show Raman spectra with a dominant A1 mode at 174 cm−1. Raman spectra analysis conform that doesn’t peak present secondary phases like Cu2S and In2S3. AFM images of the as-deposited thin films show adherent, compact, and crack-free surface. The (αhν)2 fall is sharper in CuInSe2 thin films with TEA complex than the TMAH complex due to better crystallinity. From the electrochemical impedance spectroscopy (EIS) study, we found that CuInSe2 thin film with TEA complex acquires a very slighter charge transfer resistance (Rct) of 32 Ω when compared with CuInSe2 thin film samples deposited with and without TMAH. Also, photoelectrochemical investigation signifies that CuInSe2 thin films deposited with TEA complex exhibit engendering better photocurrent response and more rapid relocation of photo-induced charge carriers in contrast to the other thin films fabricated with TMAH. We observed from cyclic voltammetry (CV) studies that redox reaction of iodide/triiodide (I−/I−3) optimized using CuInSe2 thin film with TEA complex delivers superior electrocatalytic performance than the films with TMAH.

Aqueous spray pyrolysis of CuInSe2 thin films: Study of different indium salts in precursor solution on physical and electrical properties of sprayed thin films

Herein, we deposited CuInSe2(CISe) thin films by using aqueous spray deposition method and post selenization process. The effect of different indium precursor salts including indium chloride, indium nitrate and indium acetate on the structural, morphological, optical and electrical properties of sprayed CISe layers has been studied by using x-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM-EDS), optical transmission (UV–Vis), Mott-Schottky analysis, I–V dark measurements. Although all the deposited thin films show a chalcopyrite tetragonal ordering structure of CISe, the crystallinity, morphology, and electrical characteristics are strongly influenced by the type of indium salt. A highly compact film with large grains (500–1000 nm) can be obtained after selenization of deposited film from indium chloride precursor while indium nitrate precursor results in low grains size and indium acetate precursor leads to rough surfaces with very small grain size. According to Mott-Schottky results, all films are p-type with carrier concentration in the range of ~1017 cm−3 to ~1019 cm−3 and the smallest value of 2.8 × 1017 cm−3 is obtained for CISe film deposited from indium nitrate precursor. The XRD and J-V dark results revealed that the CISe films deposited from indium chloride precursor demonstrates better crystallinity and higher mobility relative to other precursors.

Analysis and Growth Modeling of CuInSe2 Films by Electrodeposition for Photocell Applications

CuInSe2 (CIS) thin films were deposited onto FTO/glass substrates by continuous current potentiostatic electrodeposition method. The aqueous deposition bath was prepared from a pH = 3.0 NaBF4 supporting electrolyte, containing CuSO4, In2(SO4)3, and SeO2 precursors. The characterization of these samples was done by scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffractometry, Raman spectroscopy, and optical spectroscopy. The experimental techniques have allowed the understanding of the atomic concentration dynamics of samples, and its relationship with the concentration of precursors. It was obtained p-type polycrystalline semiconductor samples, with 0.95 eV gap energy; the crystalline quality of these samples was also verified. Besides this, the nucleation and growth of CIS were studied during its electrochemical deposition on top of FTO, and vitreous carbon electrodes. Chronoamperometry I-t plots permitted the study of current transients, through classic nucleation models, which were used to understand the nucleation mechanism which occurred during the electrodeposition process, besides predicting some of its characteristic properties, as its diffusion coefficient, density of active sites, and nucleation rate constant per active site. Atomic force microscopy measurements were used to investigate the first stages of growth of these CIS films, deposited at different overpotentials. Preliminary devices CIS/In2Se3/FTO were mounted, with In2Se3 (IS) film also deposited by continuous current electrodeposition. Its electrical properties were analyzed, revealing a Schottky diode like behavior; there were observed light dependent open circuit voltage generation and resistance drop, disclosing promising characteristics for photovoltaic production.

SYNTHESIS OF CHALCOPYRITE CuInSe2 (CIS) NANOSHEETS USING VITAMIN C AS AN ADJUVANT AND PHOTOELECTRIC PROPERTIES OF CIS THIN FILMS

To prepare chalcopyrite-phase CuInSe2 (CIS) nanosheets, green reductants were screened by using them to reduce the valence state of copper sources using a N,N-dimethylformamide/triethylene glycol(DMF/TEG) mixed solvent. CuCl was used as the copper source, indium chloride as the indium source, selenium powder as the selenium source, TEG as the anionic solvent, DMF as the cationic solvent, and Vitamin C (Vc) as the reductant. The influences of reaction temperature, reaction time, and Vc amount on the phase and composition of synthetic CuInSe2 nanosheets were examined, and the results were used to propose a reaction mechanism. The optional reaction conditions were a reaction temperature of 260 oC, a reaction time of 16 h, and a Vc amount of 0.20 g. Chalcopyrite-phase CIS nanosheets were synthesized with particle sizes of 14 µm and a uniform particle size distribution. CuInSe2 thin films displayed good surface smoothness and compactness in a 5.5 µm spin-cast film. The thin film showed a bandgap of 1.08 eV, a carrier concentration of 5.26×1016 cm-3 , and a carrier mobility of 150.41 cm2 V -1 S -1 . The results showed that this strategy can be used to prepare chalcopyrite-phase CIS which could be used as a photosensitive layer for various optoelectronic devices.

Investigation of precursors concentration in spray solution on the optoelectronic properties of CuInSe2 thin films deposited by spray pyrolysis method

Copper indium selenide CuInSe2(CISe) thin films were deposited by chemical spray pyrolysis (CSP) method of CuInS2(CIS) and subsequent selenization process. To study the effects of solution concentration, we prepared different precursors solution of CIS including different amount of indium salts from 0.025 to 0.100 M with In/Cu 1.25 and S/In 4. These results propose that solution concentration is critical for inflecting the morphological, optical, electrical, and electrochemical characteristics of solution-processed CISe films and device performance. The studied morphological properties of deposited samples were homogenous, crack-free with large grains in indium salt concentrations more than 0.075 M. The deposited film thickness depends on the spray precursor concentration and increases for higher concentration. In addition with increasing of indium precursor concentration from 0.025 to 0.100 M in spray solution, the optical bandgap of deposited film decreases from 1.40 to 1.35 eV. Also the films mobility and carrier density were notably influenced by any change in the solution concentration. Electrical and electrochemical properties showed a decrease in carrier density from ~ 1020 to ~ 1017 cm−3 and the increase in mobility of order ~ 10–7 to ~ 10–2 cm2/V s, respectively, for 0.025 M, 0.100 M CISe films. All films exhibited p-type conductivity owing to different concentrations. However, it seems that the concentration of the ideal solution is 0.100 molars.

FABRICATION AND CHARACTERIZATION OF CuInSe2 THIN FILM SOLAR CELLS WITH FLUORINE DOPED ZnO AS NEW BUFFER LAYER

Copper indium diselenide CuInSe2 (CISe) thin films are very important semiconductor material for solar cell applications.In this study, CuInSe2 (CIS), and Fluorine doped ZnO (ZnO:F) thin films were electrodeposited from aqueous solutions consisting of CuCl2, InCl3,and SeO2 with Na-citrate as complexing agents onto Fluorine doped tin oxide (FTO) substrates for CuInSe2,and ZnCl2,NH4F were used as sources of ZnO and fluorine doping respectively. The microstructures, morphologies, and optical properties of the CuInSe2 With new buffer layer fluorine doped ZnO (FZO) were characterized. X-ray diffraction analysis showed that all the films CuInSe2 are tetragonal chalcopyrite with favored orientation along (112) direction and Cu:In:Se crystals are nearly 1:1:2 atomic ratio. The surface morphology of all layers were void free, compact and fairly uniform. The near stoichiometries CuInSe2 film (annealing at 350°C), has the optica

Correlating facet orientation, defect-level density and dipole layer formation at the surface of polycrystalline CuInSe2 thin films

Individual grains of chalcopyrite solar cell absorbers can facet in different crystallographic directions at their surfaces. To gain a deeper understanding of the junction formation in these devices, we correlate variations in the surface facet orientation with the defect electronic properties. We use a combined analytical approach based on scanning tunneling spectroscopy (STS), scanning electron microscopy, and electron back scatter diffraction (EBSD), where we perform these experiments on identical surface areas as small as 2 × 2 µm2 with a lateral resolution well below 50 nm. The topography of the absorber surfaces indicates two main morphological features: micro-faceted, long basalt-like columns and their short nano-faceted terminations. Our STS results reveal that the long columns exhibit spectral signatures typical for the presence of pronounced oxidation-induced surface dipoles in conjunction with an increased density of electronic defect levels. In contrast, the nano-faceted terminations of the basalt-like columns are largely passivated in terms of electronic defect levels within the band gap region. Corresponding crystallographic data based on EBSD experiments show that the surface of the basalt-like columns can be assigned to intrinsically polar facet orientations, while the passivated terminations are assigned to non-polar planes. Ab-initio calculations suggest that the polar surfaces are more prone to oxidation and resulting O-induced defects, in comparison to non-polar planes. Our results emphasize the correlation between morphology, surface facet orientations and surface electronic properties. Furthermore, this work aids in gaining a fundamental understanding of oxidation induced lateral inhomogeneities in view of the p-n junction formation in chalcopyrite thin-film solar cells.

Electrodeposition of CuIn(Al)Se2-based thin films on various substrates

While the electrodeposition of CuInSe2-based compounds have been the topic of many research efforts, effects of the substrate have been rarely addressed in the literature. In the current study, the electrodeposition of CuIn(Al)Se2 thin films on different substrates is performed and effects of the substrate on the morphology and composition of obtained layer are studied. CuIn(Al)Se2 thin films are electrodeposited on different substrates, including copper, stainless steel (SS), and titanium foils as well as fluorine-doped tin oxide (FTO) transparent electrode. Electrodepositions are performed in sulfate solution of Cu2+, Al3+, In3+, and Se4+ ions. The results from cyclic voltammetry (CV), composition and phase analyses indicate that the incorporation of In and Al is a function of the co-deposition potential in cathodic scanning process and the lowest co-deposition potential of − 0.9 V is observed on FTO substrate. Characterizations of deposited films by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis have also revealed that the deposited films on FTO and Ti substrates contained a layer with high amount of In, Al (In + Al > 7 wt%) and CuIn(Al)Se2 phase with chalcopyrite structure while the deposited film on Cu substrate mainly consists from binary Cu-Se phases. The deposited films on FTO and SS substrates have large particles (> 400 nm) with partly laminar morphology while fine microstructures are obtained for films deposited on Cu (300 nm) and Ti (80 nm) substrates. In addition, by combining the crystallographic information and thermodynamic relations, a method is proposed to predict the favored phase on each support which are in a good agreement with experimental observations.

Structural, SEM and Nucleation Characterization of Electrochemically Synthesized CuInSe2 Thin Films

Near-stoichiometric CuInSe2 thin films were synthesized by one-step electrodeposition on molybdenum-coated glass substrates. Cyclic voltammetry measurements were firstly used to investigate the electrodeposition mechanisms. The electrochemical, structural, composition and nucleation properties of these films were investigated by cyclic voltammetry, scanning electron microscopy (SEM) and x-ray diffraction (XRD) using an energy dispersive x-ray spectrometer. Analysis of the nucleation mechanisms indicated that the electrodeposition of CuInSe2 from a single bath solution involved an instantaneous 3-D nucleation. An appropriate deposition-imposed potential range of −700 to −400 mV/SCE was determined, although the reduction peak of indium occurred around −960 mV/SCE. The most suitable deposition potential for film preparation was determined to be −500 mV/SCE. The XRD results showed that the films exhibit a polycrystalline tetragonal CuInSe2 phase with (112) orientation. The composition of the film deposited at −500 mV/SCE is very close to the stoichiometric ratio of 1:1:2 according to energy-dispersive x-ray spectroscopy measurements. We discuss the results obtained for the SEM and structural properties of the latter films, which were subjected to a post-annealing process under vacuum at temperatures of 300, 400 and 500°C for 30 min.

Investigation of near-stoichiometric polycrystalline CuInSe2 thin films by photoreflectance spectroscopy

The bandgap of CuInSe2 thin film photovoltaic absorbers depends on the Cu content, although the nature of this dependence is still a matter of debate. While theoretical results predicted a widening or stable bandgap with decreasing Cu content, the few experimental data available point to a narrowing of the bandgap. Here, we apply photoreflectance spectroscopy at room temperature to near-stoichiometric polycrystalline CuInSe2/CdS heterojunctions with a lateral Cu gradient to analyze the electronic transitions in the vicinity of the fundamental absorption edge of CuInSe2 absorber as a function of Cu deficiency. The results indicate that the lowest bandgap transition at 1.02 eV notably decreases by 20–30 meV for slightly Cu deficient samples, strengthening the case for an association of a lower Cu content with a narrower bandgap. In contrast, the higher energy transition at 1.25 eV does not show a redshift, which requires further theoretical explanation.

Development of CuInSe2 thin films by SELD method for photovoltaic absorber layer application

CuInSe2 (CIS) films were obtained on annealing of 280 nm and 775 nm thick Cu/In/Se stacks deposited on corning glass substrate. The stacked elemental layer deposition (SELD) technique was used for the deposition of the films of Se, In and Cu layers. The as-deposited and annealed samples were found to possess polycrystalline structures. The films provided dominating CIS phase along with secondary phases of Cu11In9, CuSe and Se. The secondary phases present in the films vary with change in annealing temperatures. Moreover, single CuInSe2 phase is observed in the 280 nm films at 523 K. The scanning electron microscopic images of the samples show nano-rod type structures of CIS grains. The elemental composition of Cu:In:Se approaches 1:1:2 in 280 nm thick samples. The ratio, however, deviates in the 775 nm thick films. The Raman spectra of these samples give A1 mode at 173 cm−1 and confirm the presence of CIS phase. The films exhibit slow increase in the band gap (Eg) values from 1.09 to 1.22 eV for 775 films. However, comparatively higher band gap (Eg) values from 1.25 to 1.90 eV are observed for 280 nm films with high absorption co-efficient (α ~ 105 cm−1) values. The films present more useful electrical parameters for 280 nm thick samples as compared to 775 nm samples due to dominated CIS phase. Thus, obtained CIS thin films of 280 nm thickness provide viable alternative as an absorber layer in solar cell structure.

Chemically Deposited CuInSe2 Thin Films and their Photovoltaic Properties: A Review

Chemically Deposited CuInSe2 Thin Films and their Photovoltaic Properties: A Review

Fabrication of n-In6Se7:Sn/p-CuInSe2 heterojunction diode on FTO coated glass substrates using reactive evaporation technique

The heterojunction diode using Sn doped In6Se7 and CuInSe2 thin films are fabricated on FTO coated glass substrates using reactive evaporation technique. The structure of CuInSe2 film is studied using XRD analysis and the film exhibits polycrystalline nature. XPS result confirms that the prepared sample is nearly stoichiometric. The I–V measurements of FTO/n-In6Se7:Sn/p-CuInSe2/Ag heterojunction diode, in dark condition, shows rectification behavior. The knee voltage and ideality factor of the diode are observed to be 1.52 V, 3.09 V and 5.57, 16.16 respectively when the Sn dopant concentration varied from 0.47 at% to 1.57 at%. The absence of photoresponse from the diodes under illumination condition is explained using the energy band structure of the heterojunction.

Composition Tuning of Single Step Electrodeposited CuInSe2 Thin Films Using Sodium Dodecyl Sulfate as Additive

CuInSe2 (CISe) thin films were electrodeposited on FTO substrates by single step deposition technique from an aqueous solution containing CuCl2, InCl3, HSeO3− ions and citric acid-sodium dodecyl sulfate (SDS) as the pH adjuster and additive, respectively. The effect of SDS concentration on the structural, composition, morphology and photo-electrochemical properties was characterized by SEM/EDAX, XRD, Raman and electrochemical (PEC) studies. The linear sweep voltammetry (LSV) and electrochemical impedance (EIS) results revealed that the addition of SDS limits the Cu-Se incubation time and enhances the diffusion controlled process which is considered to be the origin of the compositional and morphological tuning nature of the SDS in CISe deposition. The structural, compositional and PEC analysis revealed that for SDS concentration less the critical micelle concentration has almost no effect in controlling the Cu2Se secondary phase. The samples deposited in the presence of SDS (> 8 mM) exhibited better PEC properties due to the reduced Cu2Se phase. Further, the Mott–Schottky analysis of all the as-deposited thin films exhibited p-type conductivity.

Electrochemical Atomic Layer Deposition of CuInSe2 on Au Surface

CuInSe2 (CIS) thin film growth on Au/glass slide surface was investigated by electrochemical atomic layer deposition (E‐ALD) in superlattice sequence in ambient laboratory conditions without any heat treatment processes involved. The electrochemical behavior of Cu, In, and Se on the Au surface was surveyed, the underpotential deposition phenomena of In was demonstrated for the first time and a various set of potentials for the three elements were considered to fabricate thin CIS films by specific superlattice sequencing. The crystal structure, elemental composition, topography, and photoelectrochemical behavior of each film produced were evaluated with the aim of finding a new set of conditions for producing stoichiometric CIS films. A good stoichiometric film of Cu0.99In0.98Se2.00 was successfully prepared by applying 50 periods of the superlattice sequence of 3(In aSe b) + 1(Cu cSe d) with the new deposition potentials of 0.08, −0.55, and −0.05 V for Cu, In, and Se precursor solutions, respectively. The resulting E‐ALD film was found to exhibit a p‐type semiconductivity.

Vacuum-Free and Highly Dense Nanoparticle Based Low-Band-Gap CuInSe2 Thin-Films Manufactured by Face-to-Face Annealing with Application of Uniaxial Mechanical Pressure

Copper indium gallium sulfo-selenide (CIGS) based solar cells show the highest conversion efficiencies among all thin-film photovoltaic competition. However, the absorber material manufacturing is in most cases dependent on vacuum-technology like sputtering and evaporation, and the use of toxic and environmentally harmful substances like H2Se. In this work, the goal to fabricate dense, coarse grained CuInSe2 (CISe) thin-films with vacuum-free processing based on nanoparticle (NP) precursors was achieved. Bimetallic copper-indium, elemental selenium and binary selenide (Cu2−xSe and In2Se3) NPs were synthesized by wet-chemical methods and dispersed in nontoxic solvents. Layer-stacks from these inks were printed on molybdenum coated float-glass-substrates via doctor-blading. During the temperature treatment, a face-to-face technique and mechanically applied pressure were used to transform the precursor-stacks into dense CuInSe2 films. By combining liquid phase sintering and pressure sintering, and using a seeding layer later on, issues like high porosity, oxidation, or selenium- and indium-depletion were overcome. There was no need for external Se atmosphere or H2Se gas, as all of the Se was directly in the precursor and could not leave the face-to-face sandwich. All thin-films were characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV/vis spectroscopy. Dense CISe layers with a thickness of about 2–3 µm and low band gap energies of 0.93–0.97 eV were formed in this work, which show potential to be used as a solar cell absorber.

An attempt to co-deposit photovoltaic quality CuInSe2 thin films: effect of surfactant and deposition potential

CuInSe2 (CISe) thin films were prepared by single step electrodeposition technique using citrate-SDS electrolyte. Preliminary studies revealed that the initial deposition conditions have significant influence over the composition, film quality and the addition of SDS in the citrate electrolyte enhances adhesion, smoothness and eliminates multinuclear growth. To explore the capability of the citrate-sodium dodecyl sulfate (SDS) electrolyte, the CISe thin films deposited at various potentials were annealed at 300 °C in nitrogen atmosphere. The structural, morphological and compositional properties of the annealed CISe thin films were compared. Finally, CISe thin film deposited at − 0.65 V/SCE exhibiting the p-type electrical conductivity was confirmed by Mott–Schottky (M–S) and photoelectrochemical (PEC) studies.