Copper Indium Diselenide Thin Films Research Articles

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.

Studies on the graded band-gap copper indium di-selenide thin film solar cells prepared by electrochemical route

A graded band-gap CuInSe2 (CIS) thin film solar cell (TFSC) having glass/FTO/CdS/CIS multilayer/Au structure has been fabricated. A simple and low-cost electrodeposition technique is used to deposit the multilayers of CIS onto fluorine doped tin oxide (FTO) coated glass substrate. A conventional three-electrode geometry consisting, FTO, graphite and Ag/AgCl as a working, counter and reference electrodes, respectively was used for electrodeposition. Structural characterization was carried out using X-ray diffraction (XRD) and Raman spectroscopy, which revealed the chalcopyrite tetragonal CIS structure with a quite Cu-rich surface which reduces upon selenization. The morphology of the as grown and selenized CIS multilayer thin films was studied by using atomic force microscopy (AFM) which shows the compact and uniform layer formation. The depth profile distribution of individual elements in both as-grown and selenized CIS multilayer thin films has been determined using secondary ion mass spectroscopy (SIMS). SIMS results revealed that the proposed graded band gap structure is retained even after selenization. The presence of Cu+, In3+ and Se2− oxidation states were confirmed using X-ray photoelectron spectroscopy (XPS). A single layer and multilayer CIS solar cell devices yielded ∼5.10% and ∼7.20% power conversion efficiency, respectively. In the present work, pH 3 buffer solution helps to improve the morphology of CIS layer which gives the better power conversion efficiency as compared to the previously reported value.

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.

The effect of citric acid and selenization onto electrochemically deposited Copper-Indium thin films for solar cell applications

Copper Indium diselenide (CISe) layers have been synthesized via two stage processes; electrodeposition of Copper-Indium (Cu-In) and selenization. The effect of complexing agent, citric acid (CA) was studied on the growth of Cu, In and Cu-In layers. Polycrystalline Cu-In layers were electrodeposited from aqueous bath at −0.85V versus Ag/AgCl reference electrode. The structural, optical, morphological, compositional, photoelctrochemical and optoelectronic properties for Cu-In layer and selenized Cu-In layers are studied. Three prominent reflections of tetragonal crystal structure of CISe, (112), (204/220) and (312/116) were exhibited in selenized layers. Nearly uniform, void-free surface morphology was observed in selenized samples. Upon selenization of Cu-In layers prepared with 0.1M CA produced stoichiometric CISe thin films. The energy band-gap values are estimated between 1.05eV to 1.18eV. Photoelectrochemical cell measurement revealed the growth of p-type and n-type conductivity of CISe thin films. The peaks related to chalcopyrite CISe and ordered defect compound are observed in Raman analyses. The superstrate solar cell structure prepared with selenized Cu-In layer deposited in presence of 0.1M CA measured 4.05% efficiency. The values of Rs, 7.42Ω-cm2, 0.94Ω-cm2 and G, 1.01mS/cm2 10.25mS/cm2 were calculated under dark and illuminated condition, respectively. We believe that the measured efficiency is low; however the further improvement is possible by optimizing the surface treatment conditions.

Agitation dependent properties of copper indium diselenide thin films prepared by electrochemical route

CuInSe2 (CIS) thin films have been prepared by potentiostatic electrochemical synthesis route in an aqueous medium. A conventional three-electrode electrochemical geometry was used to study the influence of agitation on electrodeposition of CIS. The co-deposition potentials for Cu-In-Se, −0.4V and −0.6V were optimized by using cyclic voltammetry measurements. The diffusive controlled growth with instantaneous nucleation is observed by Chronoamperometric measurements. X-ray diffraction (XRD) and Raman spectroscopy, UV–Vis spectroscopy, energy dispersive X-ray analysis (EDAX) and scanning electron microscopy (SEM) were employed to study the structural, optical, compositional and morphological properties, respectively. Polycrystalline CIS thin films with tetragonal structure were obtained without agitation, however the secondary phases of CuxSey were attributed with agitation. The Raman results are found to be in good agreement with XRD and EDAX analyses. Without agitation the energy band gap (Eg) was estimated ~1.1eV. The higher values of Eg~1.5 to 1.8eV measured for the samples grown with agitation are proposed due to the inhomogeneous growth of precursors and the change in surface morphology. Uniform, compact and well adherent CIS layers were deposited with and without agitation. The deposition potentials and agitation conditions were found to be greatly affected on the surface morphology. The stoichiometric CIS layer was deposited at −0.6V without agitation.

Study of electrochemically grown copper indium diselenide (CIS) thin films for photovoltaic applications

CIS thin films have been grown electrochemically from an aqueous electrolyte at room temperature on fluorine doped tin oxide coated glass substrate at different deposition potentials ranging from −0.7 to −1.0 V versus Ag/AgCl reference electrode. Cyclic voltammetry was studied at slow scan rate to optimize the deposition potential. The thin film samples were selenized in a tubular furnace at 400 °C for 20 min. X-ray diffraction and Raman analysis was used to study the structural properties. Optical absorption, scanning electron microscopy and energy dispersive X-ray analysis (EDAX) have been used to investigate the band-gap, surface morphology and compositional analysis. Electrical properties were studied with the help of current–voltage measurements. Conductivity type for CIS thin films was studied by using photo-electrochemical study. The prominent reflections (112), (204/220) and (312/116) of tetragonal chalcopyrite CIS have been revealed for all as-grown and selenized samples. The energy band gap of the selenized CIS thin film deposited at various deposition potentials was found to be ~1.03 to 1.24 eV. Granular, uniform and void free surface was observed in as-prepared sample, while large clusters were noticed in selenized samples. EDAX results reveal that the stoichiometric CIS thin film are deposited −0.8 V, however, Cu-rich and In-rich CIS layers were grown at lower and higher cathodic deposition potentials, deviated from −0.8 V. The values ideality factor (η) calculated from I–V measurements were found to be decreased upon selenization. The Raman spectra of stoichiometric CIS thin film shows dominant A1 mode with spectral features sensitive to the microcrystalline quality of the layers. A ordered defect compound layer and secondary phases of CuSe are observed in In-rich and Cu-rich CIS layers, respectively.

Improving conversion efficiency of co-electrodeposited CuInSe2 thin film solar cells with substrate and solution heating

As-prepared electrodeposited CuInSe2 film is amorphous and rough. After CuInSe2 films growth, cadmium sulfide layers are deposited by chemical bath. The interface between the CuInSe2 layer and the CdS layer is a p–n junction for high-efficiency solar cells. The CuInSe2 layer must be defect-free and smooth to make a junction. In this work, CuInSe2 films with a smooth surface are obtained by heating the substrate and solution, and the solar cell of open circuit voltage is improved from 69 to 371 mV, the fill factor from 26.3 to 52 % and the conversion efficiency from 0.49 to 6.46 %. The structural properties of these selenized films are investigated using X-ray diffraction (XRD). Field-emission scanning electron microscopy images indicate that the ordered copper indium diselenide thin films are entirely filled. XRD results show that the copper indium diselenide thin films are crystalline with highly preferential orientation. Energy-dispersive spectroscopy analysis was used to determine the composition of the films.

Low-temperature, rapid thermal annealing of CIS thin films deposited by using a co-sputtering process with in and CuSe2 targets

Polycrystalline copper-indium-diselenide (CIS) thin films deposited by using co-sputtering with CuSe2 and In targets were prepared without any additional Se-containing gas for rapid thermal annealing (RTA) in a N2 ambient. RTA was used for a short annealing duration at a relatively low annealing temperature to control the chemical composition ratio of Se by minimizing the volatilization of Se. CIS chalcopyrite (112), (220)/(204), and (312)/(116) phases were clearly found in the samples treated using RTA without a Se-containing gas. The optical band gap energy of the RTAtreated CIS thin films was in the range of 1.12–1.34 eV and varied with the In content, but the deviation parameter, Δm, showed an opposite trend. The mean absorbance of the RTA-treated CIS thin films was 1.24, corresponding to an absorption of approximately 91.7% of the incident light in the visible and the near-infrared regions. Excessive holes with a carrier concentration of 1021 cm-3 were found in the RTA-treated p-type CIS thin films and led to a decrease in the resistivity to 10-3 O-cm, which was found to have been due to the short-duration annealing at low-temperature.

Crystalline photoactive copper indium diselenide thin films by pulsed laser crystallization of nanoparticle-inks at ambient conditions

Direct pulsed laser crystallization (DPLC) is explored to rapidly crystallize large area coated copper indium diselenide (CIS) nanoparticle-inks.

Reaction pathways for copper indium diselenide thin film formation from single and multiple InSe/CuSe bilayer stacks

The influence of precursor stack structure on the formation of CuInSe2 (CIS) thin films was investigated by structure characterization of samples with single and multiple InSe/CuSe bilayer stacks deposited by co-evaporation on Mo/glass substrates. With an increase in the number of stacks, the temperature for complete grain growth decreased, but the grain size in the resulting CIS thin films was small. The low crystallization temperature could be attributed to the low activation energy for nucleation, which in turn afforded a nanocrystalline CIS phase even during low-temperature evaporation. Because of the large grain size (1.3μm) in the resulting CIS film and low crystallization temperature, the precursor structure with two alternating InSe/CuSe stacks was concluded to be optimal for solar cell applications; such a structure would have the appropriate number of nucleation sites for complete CIS crystallization to afford a large grain size.

Correlation between sprayed CuInSe2 thin films properties and deposition temperature

Copper indium diselenide thin films were prepared by spray pyrolysis technique on glass substrates at different deposition temperatures ranging from 150 to 300 °C. XRD patterns of sprayed CuInSe2 films showed that all films are polycrystalline with a chalcopyrite structure and a preferential orientation along the (112) direction. The chemical composition analysis showed that the Cu/In ratio increased with increasing the deposition temperature. The atomic force micrographs show that the elaborated films have a uniform surface morphology with a homogeneous distribution of crystallites. The electrical conductivity of the prepared films increased with increasing the deposition temperature. The energy band gap of prepared films decreased with increasing Cu/In ratio.

Effect of growth potential on the electrodeposition of CIS thin films

Thin films of copper indium diselenide (CIS) were prepared in aqueous bath by low-cost potentiostatic electrodeposition technique onto Fluorine doped tin oxide substrates. The deposition potential was optimized using cyclic voltammetry study in a ternary Cu–In–Se system. The films were characterized systematically with the aid of UV–Vis spectroscopy, IV measurements, X-ray diffraction, Scanning electron microscopy and Energy dispersive X-ray analysis. CIS films deposited for different growth potential shows the tetragonal structure with (112) preferential orientation. Annealing of the films at temperature 400°C not only improves the crystallinity of layers, but it also increases the grain size, which is suitable for the development of high efficiency solar cells.

CuInSe 2 films prepared by three step pulsed electrodeposition. Deposition mechanisms, optical and photoelectrochemical studies

p-Type semiconducting copper indium diselenide thin films have been prepared onto In 2O 3:Sn substrates by a recently developed pulse electrodeposition method that consists in repeated cycles of three potential application steps. The Cu–In–Se electrochemical system and the related single component electrolytes were studied by cyclic voltammetry to identify the electrode processes and study the deposition processes. In situ atomic force microscopy measurements during the first 100 deposition cycles denote a continuous nucleation and growth mechanism. Particles removed by film sonication from some of the films were characterized by transmission electron microscopy and determined to consist in nanoscopic and crystalline CuInSe 2. The remaining film is still crystalline CuInSe 2, as assessed by X-ray diffraction. The chemical characterization by combined X-ray photoelectron spectroscopy, X-ray fluorescence and inductively coupled plasma optical emission spectroscopy, showed that films were Cu-poor and Se-poor. Raman characterization of the as-grown films showed that film composition varies with film thickness; thinner films are Se-rich, while thicker ones have an increased Cu–Se content. Different optical absorption bands were identified by the analysis of the UV–NIR transmittance spectra that were related with the presence of CuInSe 2, ordered vacancy compounds, Se, Cu 2− x Se and In 2Se 3. The photoelectrochemical activity confirmed the p-type character and showed a better response for the films prepared with the pulse method.

Evaluation and Validation of Equivalent Circuit Photovoltaic Solar Cell Performance Models

The “five-parameter model” is a performance model for photovoltaic solar cells that predicts the voltage and current output by representing the cells as an equivalent electrical circuit with radiation and temperature-dependent components. An important feature of the five-parameter model is that its parameters can be determined using data commonly provided by module manufacturers on their published datasheets. This paper documents the predictive capability of the five-parameter model and proposes modifications to improve its performance using approximately 30 days of field-measured meteorological and module data from a wide range of cell technologies, including monocrystalline, polycrystalline, amorphous silicon, and copper indium diselenide (CIS). The standard five-parameter model is capable of predicting the performance of monocrystalline and polycrystalline silicon modules within approximately 6% RMS but is slightly less accurate for a thin-film CIS and an amorphous silicon array. Errors for the amorphous technology are reduced to approximately 5% RMS by using input data obtained after the module underwent an initial degradation in output due to aging. The robustness and possible improvements to the five-parameter model were also evaluated. A sensitivity analysis of the five-parameter model shows that all model inputs that are difficult to determine and not provided by manufacturer datasheets such as the glazing material properties, the semiconductor band gap energy, and the ground reflectance may be represented by approximate values independent of the PV technology. Modifications to the five-parameter model tested during this research did not appreciably improve the overall model performance. Additional dependence introduced by a seven-parameter model had a less than 1% RMS effect on maximum power predictions for the amorphous technology and increased the modeling errors for this array 4% RMS at open-circuit conditions. Adding a current sink to the equivalent circuit to better model recombination currents had little effect on the model behavior.

Single step deposition method for nearly stoichiometric CuInSe 2 thin films

This paper reports the production of high quality copper indium diselenide thin films using pulsed DC magnetron sputtering from a powder target. As-grown thin films consisted of pin-hole free, densely packed grains. X-ray diffraction showed that films were highly orientated in the (112) and/or (204)/(220) direction with no secondary phases present. The most surprising and exciting outcome of this study was that the as-grown films were of near stoichiometric composition, almost independent of the composition of the starting material. No additional steps or substrate heating were necessary to incorporate selenium and create single phase CuInSe 2. Electrical properties obtained by hot point probe and four point probe gave values of low resistivity and showed that the films were all p-type. The physical and structural properties of these films were analyzed using X-ray diffraction, scanning electron microscopy and atomic force microscopy. Resistivity measurements were carried out using the four point probe and hot probe methods. The single step deposition process can cut down the cost of the complex multi step processes involved in the traditional vacuum based deposition techniques.

Electrochemical Synthesis of CuIn ( Se , S ) 2 Layer for Thin-Film Solar Cell with a Superstrate Configuration

Copper indium diselenide thin films were grown on a fluorine-doped tin oxide (FTO) glass substrate covered with a thin layer of cadmium sulfide (CdS) by an electrodeposition method. The annealing of the films in a sulfur atmosphere resulted in a partial replacement of selenium with sulfur to form solid solutions. Structural characterizations of the annealed samples by using X-ray diffraction, energy-diffused X-ray analysis, and UV/visible/near-infrared absorption spectra revealed that the sulfur contents and the photoabsorption onsets strongly depended on the annealing temperature. The performance of superstrate-type solar cells was highest when the layer was annealed at in a sulfur atmosphere. A capacitance–voltage analysis of the junctions showed that the hole density in was increased by annealing at a high temperature, contributing to the improvement in the photocurrent. However, annealing at a high temperature led to the interdiffusion of CdS into the layer, resulting in the lowering of the solar cell performance. As a result of the trade-off between these factors, annealing at gave the best result for films made by the electrodeposition method.

Growth, structural and optical properties of copper indium diselenide thin films deposited by thermal evaporation method

Copper indium diselenide (CuInSe 2) compound was synthesized by reacting its constituent’s elements copper, indium and selenium in near stoichiometric proportions (i.e. 1:1:2 with 5% excess selenium) in an evacuated quartz ampoule. Synthesized pulverized compound material was used as an evaporant material to deposit thin films of CuInSe 2 onto organically cleaned sodalime glass substrates, held at different temperatures (300–573 K), by means of single source thermal evaporation method. The phase structure and the composition of chemical constituents present in the synthesized compound and thin films have been investigated using X-ray diffraction and energy dispersive X-ray analysis, respectively. The investigations show that CuInSe 2 thin films grown above 423 K are single phase, having preferred orientation of grains along the (112) direction, and having near stoichiometric composition of elements. The surface morphology of CuInSe 2 films, deposited at different substrate temperatures, has been studied using the atomic force microscopy to estimate its surface roughness. An analysis of the transmission spectra of CuInSe 2 films, recorded in the wavelength range of 500–1500 nm, revealed that the optical absorption coefficient and the energy band gap for CuInSe 2 films, deposited at different substrate temperatures, are ∼10 4 cm −1 and 1.01–1.06 eV, respectively. The transmission spectrum was analyzed using iterative method to calculate the refractive index and the extinction coefficient of CuInSe 2 thin film deposited at 523 K. The Hall effect measurements and the temperature dependence of the electrical conductivity of CuInSe 2 thin films, deposited at different substrate temperatures, revealed that the films had electrical resistivity in the range of 0.15–20 ohm cm, and the activation energy 82–42 meV, both being influenced by the substrate temperature.

Structural, electrical, and optical properties of copper indium diselenide thin film prepared by thermal evaporation method

Stoichiometric compound of copper indium diselenide (CuInSe 2) was synthesized by direct reaction of high-purity elemental copper, indium and selenium in an evacuated quartz ampoule. The phase structure and composition of the synthesized pulverized material analyzed by X-ray diffraction (XRD) and energy dispersive analysis of X-rays (EDAX) revealed the chalcopyrite structure and stoichiometry of elements. Thin films of CuInSe 2 were deposited onto organically cleaned soda lime glass substrates held at different temperatures (i.e. 300 K to 573 K) using thermal evaporation technique. CuInSe 2 thin films were then thermally annealed in a vacuum chamber at 573 K at a base pressure of 10 − 2 mbar for 1 h. The effect of substrate temperature ( T s) and thermal annealing ( T a) on structural, compositional, morphological, optical and electrical properties of films were investigated using XRD, transmission electron microscopy, EDAX, atomic force microscopy (AFM), optical transmission measurements and Hall effect techniques. XRD and EDAX studies of CuInSe 2 thin films revealed that the films deposited in the substrate temperature range of 423–573 K have preferred orientation of grains along the (112) plane and near stoichiometric composition. AFM analysis indicates that the grain size increases with increase of T s and T a. Optical and electrical characterizations of films suggest that CuInSe 2 thin films have high absorption coefficient (10 4 cm − 1 ) and resistivity value in the interval 10 − 2 –10 1 Ω cm influenced by T s and T a.

Empirical investigation of the energy payback time for photovoltaic modules

Abstract Energy payback time is the energy analog to financial payback, defined as the time necessary for a photovoltaic panel to generate the energy equivalent to that used to produce it. This research contributes to the growing literature on net benefits of renewable energy systems by conducting an empirical investigation of as-manufactured photovoltaic modules, evaluating both established and emerging products. Crystalline silicon modules achieve an energy break-even in 3 to 4 years. At the current R&D pilot production rate (8% of capacity) the energy payback time for thin film copper indium diselenide modules is between 9 and 12 years, and in full production is ∼2 years. Over their lifetime, these solar panels generate 7 to 14 times the energy required to produce them. Energy content findings for the major materials and process steps are presented, and important implications for current research efforts and future prospects are discussed.

Preparation and Study of Structural and Optical Properties of Chemical Bath Deposited Copper Indium Diselenide Thin Films

Copper indium diselenide thin films of different thicknesses were prepared by the chemical bath deposition technique onto well-cleaned glass substrates at room temperature. The thickness of the deposited films has been determined by gravimetry. The structural characterization was carried out by X-ray diffraction and scanning electron microscopic studies. These studies confirm the polycrystalline nature of the films with chalcopyrite structure. The structural parameters such as lattice constants, axial ratio, tetragonal distortion, crystallite size, dislocation density and number of crystallites per unit area have been evaluated. The composition of the various constituents in CuInSe 2 films has been determined by energy dispersive X-ray analysis. The optical properties have been studied in detail in the wavelength range 4000-14500 A and the optical band gap has been found to be direct and allowed.