CuInSe2 Thin Films Research Articles

Real-Time Spectroscopic Ellipsometry for Flux Calibrations in Multi-Source Co-Evaporation of Thin Films: Application to Rate Variations in CuInSe2 Deposition.

Flux calibrations in multi-source thermal co-evaporation of thin films have been developed based on real-time spectroscopic ellipsometry (RTSE) measurements. This methodology has been applied to fabricate CuInSe2 (CIS) thin film photovoltaic (PV) absorbers, as an illustrative example, and their properties as functions of deposition rate have been studied. In this example, multiple Cu layers are deposited step-wise onto the same Si wafer substrate at different Cu evaporation source temperatures (TCu). Multiple In2Se3 layers are deposited similarly at different In source temperatures (TIn). Using RTSE, the Cu and In2Se3 deposition rates are determined as functions of TCu and TIn. These rates, denoted Reff, are measured in terms of effective thickness which is the volume per planar substrate area and accounts for surface roughness variations with deposition time. By assuming that all incident metal atoms are incorporated into the films and that the atomic concentrations in the deposited material components are the same as in single crystals, initial estimates of the Cu and In atom fluxes can be made versus TCu and TIn. Applying these estimates to the co-evaporation of a set of CIS films from individual Cu, In, and Se sources, atomic concentration corrections can be assigned to the Cu and In2Se3 calibration films. The corrections enable generation of a novel calibration diagram predicting the atomic ratio y = [Cu]/[In] and rate Reff within the TCu-TIn plane. Using this diagram, optimization of the CIS properties as a PV absorber can be achieved versus both y and Reff.

Physical properties of InxSey and CuInSe2 thin films with potential application in radiation detectors

A study of InxSey and CuInSe2 thin films processed by the thermal co-evaporation technique by evaluating its physical properties is carried out. Both InxSey as well as CuInSe2 thin films were synthesized by multi-source thermal co-evaporation technique, using Knudsen-type effusion cells. The optical, structural, electrical, and morphological properties of each film were analyzed in order to determine the feasibility at the formation of a p-CuInSe2/n-InxSey heterojunction. InxSey films exhibited bandgap values in the range of 2.4–2.7 eV which was determined by UV–vis spectroscopic analysis. Vibrational modes associated to In2Se3 as well as Se are presented in the InxSey films according to Raman studies. The irregular morphology of the grains on the InxSey surface, with an average size of 380 nm are related to both In2Se3 and Se materials according to Raman spectroscopy and Scanning Electron Microscopy analysis. The InxSey thin films showed resistivity vales around 10–3 Ω·cm. The Hackee´s figure of Merit (FOMH) analysis supported the physical assumption that InxSey thin films are feasible to be used as window layer in a photovoltaic device because of the high values of FOMH obtained for samples processed at 300 °C. On the other hand, an influence on the morphology of the CuInSe2 films was observed when the films were synthetized at different substrate temperature. Uniform CuInSe2 films with agglomerated cauliflower-like grains with an average size of 1.8 μm were observed by SEM. The presence of binary phases within the CuInSe2 compound were detected through Raman and x-ray characterization. Average crystallite size of 61 nm and microstrain around 2.5 × 10–3 were estimated for the CuInSe2 films through x-ray analysis. According to the physical properties analyzed the InxSey/CuInSe2 semiconductor bilayer can be a suitable candidate for application in photovoltaic devices as well as charged particle detector.

Influence of choline chloride pH adjuster on physical and optical properties of CuInSe2 thin films by CBD

We concentrate on low-cost thin film solar cells with the help of choline chloride acting as a pH adjuster because copper ternary material compounds and their alloys have become more and more lavish over the past 20 years. Chemical Bath Deposition (CBD) is used to produce copper indium selenium (CuInSe2) thin films on glass substrates while a pH adjuster is present. The micro structural and elemental properties are studied using X-ray diffraction (XRD), Raman, Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscopy (EDS). The optical studies of CuInSe2 thin films are done using a UV–Vis–NIR spectrometer. XRD and Raman spectra shows that the CIS thin films deposited in the sequence of Glass/In/Se/Cu2Se/Se (labeled as CISB) and annealed at 400 °C (CISB400) contains all the peaks corresponding to the chalcopyrite CuInSe2. From the EDS measurements it was noted that the selenium to metal ratio (Se/Cu + In) for all the samples changes with temperature. It is worth to note that the film thickness decreases with a decrease in the pH of choline chloride which results a change in the optical band gap of the films. The optical properties of these thin films are greatly influenced by adjusting pH and it gives better results for optoelectronic devices with a sustainable UV filter which absorbs more in ultraviolet vicinity. The energy gap (Eg) values of the CISB samples were determined and is found to be suitable for photovoltaic conversion process.

Electrochemical deposition of Cr3+ doped CuInSe2 thin films for electrocatalytic activity and photovoltaic performance

Pure CuInSe2 and CuInSe2 thin films doped with different mole percentage concentrations (1 to 5 mol%) Cr3+were deposited through a one-step electrochemical deposition technique on an ITO glass substrate. The XRD pattern displayed the structural information of the pure CuInSe2 and Cr3+incorporated CuInSe2 thin films, where all elaborated films show tetragonal structure along with (200) plane orientation. The microstructural features of CuInSe2 thin films and Cr3+doped CuInSe2 have been examined with the help of an atomic force microscope, and the surface roughness was estimated. The AFM result shows the pure and Cr3+doped CuInSe2 thin films were homogeneous, nanocrystalline particles agglomerated, void-free, compact, and well-adhesive which reveals the films having a good morphology with a hillock structure. The EIS outcomes indicate that the CuInSe2 thin film obtained from 3 mol percent Cr3+ions doped CuInSe2 thin film shows very low charge transfer resistance, so it has high conductivity. Photoelectrochemical activity confirmed that 3 mol percent Cr3+ion doped CuInSe2 had superior photocurrent responsibility among them. It was observed from CV analysis that the optimized 3 mol percent of Cr3+ions doped CuInSe2 possessed greater electrocatalytic performance towards the reduction of I3-. The Raman spectrum of single crystallized CuInSe2 thin films shows that A1 dominates mode at174 cm-1. The Raman spectral studies confirmed that only the ternary phase of CuInSe2. Solar light irradiation with an intensity of 100 mW/cm2 on 3 mol% Cr3+ doped CuInSe2 thin film cell resulted in a power conversion efficiency of 8.23%.

Formation, Enhanced Crystallization, Optical Absorption and Electrical Conduction in Copper Indium Selenide Thin Films Prepared via Pulse Laser Welding Technique

AbstractIn this study, thin films of CuInSe2 (CIS) are expeditiously fabricated within 1 s utilizing the pulsed laser welding (PLW) technique. Preceding the PLW process, thin films of InSe (500 nm) are coated with Cu nanosheets of 60 and 120 nm thicknesses using vacuum coating systems. The optimal PLW parameters leading to the formation of CIS films include a pulse width of 1.0 ms, a spot diameter of 2.0 mm, and a repetition frequency of 10 Hz. The resulting CIS films exhibited a well‐crystalline cubic structure with lattice parameters of 5.265 Å. Surface morphology analyses revealed the preferential formation of porous films with varying stoichiometry, a characteristic that can be manipulated by adjusting laser welding parameters. The energy band gap and room temperature electrical conductivity display values of 1.80 eV and 2.06 × 10−5 (Ωcm)−1, respectively. Cu‐rich samples exhibit a wider energy band gap of 1.94 eV and lower electrical conductivity values of 4.78 × 10−7 (Ωcm)−1. The CIS film demonstrates n‐type conductivity attributed to the formation of donor levels centered at 0.24 and 0.10 eV. This study presents an ultrafast method for fabricating CIS films with physical properties compatible with those produced using traditional methods.

Triple junction solar cell with Cu In1-x Gex Se as absorbents layers

The design of multi-junction solar cells is guided by both the theoretical optimum bandgap combinations as well as the realistic limitations to materials with these bandgaps. Nowadays, triple-junction III-V multi-junction solar cells are commonly used as GaAs, InGaAs; InGaP ... In this work, we are interested in studying triple junctions based on thin-film solar cells Cu(In1-xGax) Se2, CuInSe2, and CuGaSe2 quaternaries using Silvaco ATLAS software. Incorporating Cu(In0.34Ga0.66) Se2 as an absorber in the middle sub-cell increased the open-circuit voltage by 0.72 V. The highest cell efficiency is 20.89 % (Voc = 2.33 V, Jsc = 9.97 mA/cm2, FF = 89.62%). This triple-junction solar cell demonstrates the potential and limitations of future improvements when voltage and current are considered.

Growth of copper indium diselenide ternary thin films (CuInSe2) for solar cells: Optimization of electrodeposition potential and pH parameters

Herein, copper indium diselenide ternary (CuInSe2) thin film has been deposited on Indium Tin Oxide (ITO) coated glass substrate by electrochemical deposition technique with different potential and pH solutions. CuInSe2 thin films were deposited by one-step electrodeposition before post-depot selenization at 450 °C for 30 min. The effect of potential and pH on the structural and optical properties of CuInSe thin film have been studied using X-ray diffraction (XRD), Scanning electron microscopy (SEM), and UV–Visible spectrometer. According to the X-ray diffraction (XRD) measurements, it was observed that all samples exhibit prominent reflections (112), (204/220), and (312/116) of tetragonal CuInSe2. The films electrodeposited at −0.8 V potential shows growth and peak values increasing in the (204/220) crystal direction within a pH range of 2.2, whereas the films electrodeposited at pH 2.6 tend to favor an increase in (112) peaks. We also noticed an improvement in surface morphology and adherent of CuInSe2 thin films electrodeposited at −0.8 V applied potential from the solution having pH 2.6. The band gaps of samples electrodeposited at −0.8V potentials from pH 2.6, 2.4, and 2.2 solutions were 1.15 eV, 1.25 eV, and 1.21 eV, respectively. As part of our investigation, we used a Solar Cell capacitance simulator (SCAPS) to perform our electrodeposited films. The most effective Power conversion efficiency (PCE) was obtained for thin films electrodeposited at −0.8 V within the solution having pH 2.4.

Effect of Rubidium Fluoride on Grain Sintering and Optoelectronic Properties of Nanostructured CuInSe2 Thin Films Obtained by Solution Processing

Chalcopyrite CuInSe2 (CISe) and Cu(In, Ga)(S, Se)2 (CIGS) absorber layers, have emerged as promising alternatives in the solar cell field due to their unique properties such as power conversion efficiencies (PCEs) above 20 %, direct bandgap, and high absorption coefficient. This enables the making of high-quality PV devices with absorbers from 2 μm thick, significantly reducing the use of raw materials. Additionally, the CISe absorber layer is a desirable material for Perovskite/CIS tandem configuration with a narrow band gap at the bottom that has demonstrated PCEs close to 25 %, and potential applications in lightweight and/or flexible substrates. Recently, the addition of alkali elements such as sodium, potassium, rubidium, and cesium via post-deposition techniques (PDTs) has demonstrated an improvement in CIGS-based solar cells’ performance. In this study, 10, 20, and 30 nm thick layers of rubidium fluoride were post-deposited on CISe-films made by solution processing techniques and then selenized under a selenium-argon atmosphere to improve the CISe photoelectronic properties such as the number of charge carriers collected and grain growth, critical characteristics to ensure useful photovoltaic devices. Thus, the effect of rubidium fluorine on CISe-based solar cells was analyzed using several characterization techniques. According to the results, thin films made by an amine-thiol mixture with uniform atomic composition were obtained. The crystallinity and grain growth improved with an increase in rubidium fluoride addition. Moreover, with 10 nm of rubidium fluoride, an improvement in the lifetime of the charge carrier, photoluminescence intensity, and the number of carriers collected by the solar cells was obtained.

Surfactant assisted single step electrodeposition of CuInSe2 thin films with rich indium selenide surface over layer

Abstract In this work, we report on the electrodeposition of CuInSe2 (CIS) thin films with In2Se3 rich surface by a single step deposition technique. It was observed that the In-content deposited in CIS can be improved by the addition of sodium dodecyl sulfate as a surfactant. The presence of an In–Se rich layer was confirmed by electrochemical, compositional and Raman spectroscopy analysis. The photo-electrochemical properties of the as-deposited CuInSe2 thin films were found to be enhanced due to the presence of In–Se rich superficial layer. The presence of an In–Se layer over CIS may act as a p-n homo-junction which may be attributed as the primary reason for the improvement in the PEC properties.

Vacuum‐Healing of Grain Boundaries in Sodium‐Doped CuInSe2 Solar Cell Absorbers

AbstractAlkali metal doping and grain boundaries (GB) have been at the center of attention within the Cu(In,Ga)(S,Se)2 photovoltaics community for years. This study provides the first experimental evidence that the GB of sodium‐doped CuInSe2 thin films may undertake reversible oxidation even at room temperature, whereas undoped films may not. The findings are corroborated by cathodoluminescence imaging, secondary ion mass spectrometry, and Kelvin probe force microscopy on air‐exposed films subsequently subject to vacuum. A thermochemical assessment identifies the likely solid–gas equilibria involved. These reactions open new research questions with respect to the beneficial role played by alkali metal dopants in chalcopyrite solar cells and may steer the community toward new breakthroughs.

Effect of heat treatment temperature on preparation and characterization of CuInSe2 thin films

Effect of heat treatment temperature on preparation and characterization of CuInSe2 thin films

Numerical Study of CiS Solar Cell with CuInSe2‐Undoped Layer

Herein, a CuInSe2 thin film solar cell with an intrinsic thin layer (HIT) is modeled and simulated using SCAPS. The HIT is deposited between a thin CdS window layer of reduced thickness of 20 nm to minimize cadmium toxicity and an absorbing layer of variable thickness. The aim is to study the influence of the thickness of absorber and HIT layer, level doping and defect densities of CuInSe2 layer, and high work function (between 5 and 5.6 eV) effect on performance parameters of the solar cell. In general, a significant increase in efficiency is observed. The HIT and the absorber thicknesses are optimized to be 0.3 and 0.5 μm, respectively. A conversion efficiency of 24.2%, a V oc of 0.78 V, J sc of 45.4 mA cm−2, and an FF of 68.3% are obtained for the proposed AZO/ZnO/CdS/CuInSe2/Mo/glass. These simulation results encourage using intrinsic thin layers in CIS solar cell structure.

Radio frequency (RF) sputtered ZrO2-ZnO-TiO2 coating: An example of multifunctional benefits for thin film solar cells on the flexible substrate

A new class of engineered trimetallic oxide nanocomposite coating based on ZrO2, ZnO, and TiO2 (ZZTO) was deposited by radio frequency (RF) sputtering. The prepared ZZTO sputtered coating was characterized by different techniques and finally applied to the CISe thin film solar cells as the antireflective (AR) coating to achieve multifunctional benefits viz. self-cleaning, anticorrosion, and photocatalysis (SAP). ZZTO coating with good optical characteristics and high transmittance was obtained with excellent hydrophobic and corrosion-resistant properties. The fabricated CuInSe2 (CISe) solar cells on the flexible substrates were tested with and without AR coating to assure multifunctionality and improvement in photo conversion efficiency. The suppression of optical loss led to improved light absorption across the wide range of spectrum and boosted the short circuit current density (JSC) from 31.04 to 33.05 mA/cm2, obtaining improved efficiency from 9.11 to 10.24%. It can be ensured from the present research work that engineered ZZTO AR coating can deliver superhydrophobic surface and transparency as high as 91% under mean visible light with excellent photocatalytic and corrosion-resistant properties. Thus, engineered multifunctional ZZTO coating can pave the way to revolutionize the AR material to the extent of an ideal candidate in photovoltaic devices.

Effect of transparent substrate on properties of CuInSe2 thin films prepared by chemical spray pyrolysis

In this paper, the properties of CuInSe2 (CISe) films deposited on three transparent substrates (FTO, FTO/NiOx, FTO/MoO3) are studied. These substrates might be used for bifacial solar cells, in place of the conventional glass/Mo substrates. CISe layers are deposited by spray pyrolysis followed by a selenization process. For the same deposition conditions, the CISe layers on FTO show the largest grain size (~ 0.50 µm) and crystallinity, while FTO/MoO3 substrates result in the smallest grains (~ 0.15 µm). The optical bandgap of the CISe films ranged from 1.35 eV for FTO substrate to 1.44 eV for FTO/MoO3 substrate. All films show p-type conductivity, with the carrier densities of 1.6 × 1017 cm−3, 5.4 × 1017 cm−3, and 2.4 × 1019 cm−3 for FTO, FTO/NiOx, and FTO/MoO3 substrates, respectively. The CISe films also show different conduction, and valence levels, based on the substrate. In all cases, an ohmic behavior is observed between the CISe and substrate. The results demonstrate that CISe layer crystallinity, carrier concentration, mobility, and energy levels are strongly dependent on the chemical nature of the substrate. Bare FTO shows the most appropriate performance in terms of device requirements.

High-resolution XEOL spectroscopy setup at the X-ray absorption spectroscopy beamline P65 of PETRA III.

A newly designed setup to perform steady-state X-ray excited optical luminescence (XEOL) spectroscopy and simultaneous XEOL and X-ray absorption spectroscopy characterization at beamline P65 of PETRA III is described. The XEOL setup is equipped with a He-flow cryostat and state-of-the-art optical detection system, which covers a wide wavelength range of 300-1700 nm with a high spectral resolution of 0.4 nm. To demonstrate the setup functioning, low-temperature XEOL studies on polycrystalline CuInSe2 thin film, single-crystalline GaN thin film and single-crystalline ZnO bulk semiconductor samples are performed.

Effect of Zn and Sn incorporation on the crystallinity of spin-coated CuInSe2 thin films

Effect of Zn and Sn incorporation on the crystallinity of spin-coated CuInSe2 thin films

Temperature-dependent phase formation of CuInSe2 for self-biased, broadband Si/CuInSe2 heterojunction photodetector

Owing to the numerous applications including optical communication, night vision, remote sensing, and security monitoring, a great interest has emerged in the development of the NIR (near-infrared) photodetectors. In this study, the self-biased Si/CuInSe2 heterojunction photodetectors have been developed and the annealing temperature has been optimized. CuInSe2 thin films have been prepared using the sequential elemental layer deposition followed by annealing at 550, 600, and 650 °C. The CuInSe2 annealed at 550 °C and 650 °C revealed the mixed-phase formation corresponding to CuInSe2 (tetragonal) and Cu7Se4 (Cubic). The CuInSe2 annealed at 600 °C confirmed the transition from mixed-phase to single-phase CuInSe2 tetragonal structure. The impact of annealing temperature-dependent phase formation on the optoelectronic characteristics of Si/CuInSe2 heterojunction has been studied. The Si/CuInSe2 heterojunction formation and photodetection in the self-biased mode have been investigated under varying Halogen light intensity and wavelength-dependent light. The highly sensitive, broadband spectral response and enhanced detectivity in the self-biased mode have been explored in the vicinity of varying annealing temperatures. The optimum Si/CuInSe2 heterojunction photodetector performance was achieved at 600 °C possessing the sensitivity, detectivity, and LDR up to 2.4×103, 0.05×1012 Jones, and 68 dB under Halogen light exposure and 0.8×104, 0.55×1012 Jones and 79 dB under 980 nm light. The present study provides useful insight into the Si/CuInSe2 heterojunction development as an optoelectronic device providing the correlation between the fundamental characteristics of CuInSe2 and its development as a broadband photodetector possessing excellent device performance in the NIR range.

Optimization of the substrate temperature of narrow bandgap CIS solar cells by three stage coevaporation process

In this paper, three-stage co-evaporation method was used to prepare narrow bandgap CuInSe2 (CIS) thin-film absorber. The effect of the substrate temperature on the performance of CIS solar cells was investigated. The substrate temperatures of the CIS films varied from 420 °C to 580 °C. The microstructure structure, crystallinity, morphology, and optoelectrical performances of the CIS solar cell were investigated by various characterization methods. We found that the substrate temperature played a great role in the properties of the CIS thin films and solar cell devices: that was the CIS solar cell deposited at low temperature showed poor crystallinity, fine grain size and low efficiency, while CIS solar cell deposited very high temperature also showed high efficiency. However, high substrate temperature can lead to the Indium loss at the surface of the CIS films, although the bulk composition of CIS films did vary much at different substrate, resulting in FF (fill factor) reduce.

In-situ study of the crystallization of amorphous CuInSe2 thin films and the effect of InCl3 treatment

Amorphous CuInSe2 films were deposited by rf-magnetron sputtering onto soda-lime glass and silicon substrates. Some were treated with an InCl3 solution. The films were annealed in a nitrogen environment and studied using in-situ high-temperature x-ray diffraction. CuInSe2 recrystallization began at ∼x223C270 °C and all samples showed increasing crystallinity up to ∼x223C380 °C. The onset and completion temperatures for crystallization varied minimally between samples. The as-deposited films (no InCl3) showed CuSe phase formation at intermediate temperatures (180–250 °C). Na2O from the soda-lime glass increased net rate of crystallization. InCl3 resulted in an even greater increase to crystallization rate and largely improved the final crystalline quality.

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.