Some physical investigations on AgInS2 sprayed thin films

AgInS₂ thin films have been prepared on glass substrates by the spray pyrolysis process using an aqueous solution which contains silver acetate (AgCH₃CO₂), thiourea (SC(NH₂)₂) and indium chloride (InCl₃) as precursors. The depositions were carried out in the range of the substrate temperature from 260 to 420 °C. The value of the concentration ratio in the spray solution of indium and silver elements x=[Ag⁺]/[In³⁺] was varied from 1 to 1.5 with [In³⁺]=10⁻² M and [S²⁻]/[In³⁺] was taken constant, equal to 4. The structural study shows that AgInS₂ thin film, prepared at 420 °C using optimal concentration ratio x=1.3 crystallizes in the chalcopyrite phase with a strong (1 1 2) X-ray diffraction line. Moreover, microprobe analysis (EPMA) shows that a nearly stoichiometric composition is obtained for these experimental conditions. Indeed, the atomic percentage of elements were. 24.5, 25.0, 49.5 for Ag, In and S, respectively. On the other hand from transmission and reflectance spectra, the obtained band gap energy is 1.83 eV for such film.     

Photoluminescence studies of p-type chalcopyrite AgInS2:Sn

Chalcopyrite AgInS₂:Sn thin films were prepared by spray pyrolysis technique for a constant ratio of [Ag]/[In]=1.5 and different SnCl₄ concentrations (0.05, 0.1 and 0.2 ml) in the spray solution obtaining x=[SnCl₄]/[Ag]+[In]=0.01, 0.02, 0.04. All films were deposited at substrate temperature of 375 °C. The deposited film for which x=0.02 exhibited p-type conductivity, having band-gap energies of 1.87 and 2.01 eV. Photoluminescence (PL) studies reveal several PL bands located at 1.45, 1.68, 1.70, 1.80 and 1.88 eV at 10 K. Each one of these PL structures are related to different defects, the 1.45 eV emission is related to indium vacancies, 1.80 eV emission to interstitial silver (Ag_in) or Indium in sites of silver (Ag_In), whereas, the other emissions (1.70 and 1.88 eV) are related with a donor–acceptor pair recombination and free to bound transition, respectively, due to sulphur vacancies. Sn in excess modifies the emission bands located at 1.70 and 1.88 eV; we found that Sn reduces sulphur vacancies and PL spectra are dominated by acceptor impurities.     

Enhanced photocatalytic hydrogen production over In-rich (Ag–In–Zn)S particles

The ratio of ZnS to AgInS₂ is usually adjusted to tune the band gaps of this quaternary (Ag–In–Zn)S semiconductor to increase photocatalytic activity. In this study, the [Zn]/[Ag] ratio was kept constant. The hydrogen production rate was enhanced by increasing the content of indium sulfide. Compared to the steady H₂ evolution rate obtained with equal moles of indium and silver ([In]/[Ag] = 1, 0.64 L/m² h), that obtained with In-rich photocatalyst ([In]/[Ag] = 2, 3.75 L/m² h) is over 5.86 times higher. The number of nanostep structures, on which the Pt cocatalysts were loaded by photodeposition, increased with the content of indium. The indium-rich samples did not induce phase separation between Ag_xIn_xZn_yS_2x+y and AgIn₅S₈, instead forming a single-phase solid solution. Although the photocatalytic activity decreased slightly for bare In-rich photocatalysts, Pt loading played a critical role in the hydrogen production rate. This study demonstrates the significant effect of In₂S₃ on this unique (Ag–In–Zn)S photocatalyst.     

Synthesis and photoelectrochemical characterization of (Ag2S)x(In2S3)1−x and AgInS2−ySey

Ternary n-type AgInS₂ and AgIn₅S₅ have been synthesized selectively by homogeneous precipitation from an aqueous solution containing the prescribed amounts of AgNO₃, In₂(SO₄)₃, Na₂S₂O₃ and CH₃COOH followed by heat treatments of the resulting precipitates at 500–800°C. Quaternary n-type AgInS_2−ySe_y semiconductors were also synthesized by sintering of a mixture of as-precipitated AgInS₂ and elemental Se. Photoelectrochemical characterization of these semiconductors was studied using the photoanodes prepared in the form of sintered pellets in a polysulfide electrolyte. Compared with the relatively poor saturated photocurrent for AgInS₂ (0.7 mA/cm²) and AgIn₅S₈ (0.01 mA/cm², AgInS_1.5Se_0.5 photoanode exhibits a higher photocurrent (20 mA/cm²) under 100 mW/cm² white-light illumination. This effect has been ascribed to the development of a highly oriented chalcopyrite crsytal during the sintering process at 800°C for 2 h. The chalcopyrite is a solid solution of AgInS₂ and AgInSe₂ and has band gaps between those of AgInS₂ and AgInSe₂. An energy conversion efficiency of 0.55%, a fill factor of 0.40, and a V_oc of 0.23 V has been obtained for the oriented quarternary photoanode.     

Electrical characterization of Al, Ag and In contacts on CuInS2 thin films deposited by spray pyrolysis

The specific contact resistivity (ρ_C) for aluminum (Al), silver (Ag) and indium (In) metallic contacts on CuInS₂ thin films was determined from I-V measurements, with the purpose of having the most appropriate ohmic contact for TCO/CdS/CuInS₂ solar cells; ρ_C was measured using the transmission line method (TLM) for the metallic contacts evaporated on CuInS₂ thin films deposited by spray pyrolysis with ratios x=[Cu]/[In]=1.0, 1.1, 1.3 and 1.5 in the spray solution. The results show that In contacts have the lowest ρ_C values for CuInS₂ samples grown with x=1.5. The minimum ρ_C was 0.26 Ω cm² for the In contacts. This value, although not very low, will allow the fabrication of CuInS₂ solar cells with a small series resistance.     

Preparation of In2O3:F thin films grown by spray pyrolysis technique

Transparent conducting fluorine doped indium oxide (In₂O₃:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperature (T_s=300 °C) showed no peaks of In₂O₃:F. In the useful range for deposition (i.e. 425–600 °C), the orientation of the films was predominantly [400]. For the 4500 Å thick In₂O₃:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 Ω and average transmission in the visible wavelength rang (400–700 nm) was 88%.     

Semiconductor-sensitized solar cells based on nanocrystalline In2S3/In2O3 thin film electrodes

A possibility of semiconductor-sensitized thin film solar cells have been proposed. Nanocrystalline In₂S₃-modified In₂O₃ electrodes were prepared with sulfidation of In₂O₃ thin film electrodes under H₂S atmosphere. The band gap (E_g) of In₂S₃ estimated from the onset of the absorption spectrum was approximately 2.0 eV. The photovoltaic properties of a photoelectrochemical solar cell based on In₂S₃/In₂O₃ thin film electrodes and I⁻/I₃⁻ redox electrolytes were investigated. This photoelectrochemical cell could convert visible light of 400–700 nm to electron. A highly efficient incident photon-to-electron conversion efficiency (IPCE) of 33% was obtained at 410 nm. The solar energy conversion efficiency, η, under AM 1.5 (100 mW cm⁻²) was 0.31% with a short-circuit photocurrent density (J_sc) of 3.10 mA cm⁻², a open-circuit photovoltage (V_oc) of 0.26 V, and a fill factor ( ff ) of 0.38.     

Fabrication of CuInSe2 films and solar cells by the sequential evaporation of In2Se3 and Cu2Se binary compounds

Cu₂Se/In_xSe(x≈1) double layers were prepared by sequentially evaporating In₂Se₃ and Cu₂Se binary compounds at room temperature on glass or Mo-coated glass substrates and CuInSe₂ films were formed by annealing them in a Se atmosphere at 550°C in the same vacuum chamber. The In_xSe thickness was fixed at 1 μm and the Cu₂Se thickness was varied from 0.2 to 0.5 μm. The CuInSe₂ films were single phase and the compositions were Cu-rich when the Cu₂Se thickness was above 0.35 μm. And then, a thin CuIn₃Se₅ layer was formed on the top of the CuInSe₂ film by co-evaporating In₂Se₃ and Se at 550°C. When the thickness of CuIn₃Se₅ layer was about 150 nm, the CuInSe₂ cell showed the active area efficiency of 5.4% with V_oc=286 mV, J_sc=36 mA/cm² and FF=0.52. As the CuIn₃Se₅ thickness increased further, the efficiency decreased.     

An investigation into effect of cationic precursor solutions on formation of CuInSe2 thin films by SILAR method

SILAR deposition of CuInSe₂ films was performed by using Cu²⁺–TEAH₃ (cupric chloride and triethanolamine) and In³⁺–CitNa (indium chloride and sodium citrate) chelating solutions with weak basic pH as well as Na₂SeSO₃ solution at 70 °C. A separate mode and a mixed one of cationic precursor solutions were adopted to investigate effects of the immersion programs on crystallization, composition and morphology of the deposited CuInSe₂ films. Chelating chemistry in two solution modes was deducted based on IR measurement. The XRD, XPS and SEM results showed that well-crystallized, smoothly and distinctly particular CuInSe₂ films could be obtained after annealing in Ar at 400 °C for 1 h by using the mixed cationic solution mode.     

Study of electron-beam evaporated Sn-doped In2O3 films

Electron beam evaporated Sn-doped In₂O₃ films have been prepared from the starting material with composition of (1 − x) In₂O₃ − -x SnO₂, where x = 0.0, 0.010, 0.025, 0.050, 0.090, and 0.120. X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and X-ray diffraction analysis were carried out on the films. Luminous transmittance and electrical resistivity of the films, show weak dependence on x. The composition of the film ([Sn]/[In] atomic ratio) was found to differ from that of the starting material. In fact, the atomic ratio was higher in the film than in the starting material by a factor which increases with x (ranging from 1.0 to 2.6). There is a relatively broad resistivity minimum in the layer atomic ratio range Sn/In = 0.06 − -0.09. These results compare well with those reported in the literature for Sn-doped In₂O₃ films, prepared by pyrolitic (spray) method.     

Photoelectrochemical properties of spray deposited n-ZnIn2Se4 thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been prepared by spraying a mixture of an equimolar aqueous solution of zinc sulphate (ZnSO₄), indium trichloride (InCl₃), and selenourea (CH₄N₂Se), onto preheated fluorine-doped tin oxide (FTO)-coated glass substrates at optimized conditions of substrate temperature and a solution concentration. The photoelectrochemical (PEC) cell configuration of n-ZnIn₂Se₄/1 M (NaOH+Na₂S+S)/C has been used for studying the current voltage (I–V), spectral response, and capacitance voltage (C–V) characteristics of the films. The PEC study shows that the ZnIn₂Se₄ thin films exhibited n-type conductivity. The junction quality factor in dark (n_d) and light (n_l), series and shunt resistance (R_s and R_sh), fill factor (FF) and efficiency (η) for the cell have been estimated. The measured (FF) and η of the cell are, respectively, found to be 0.435% and 1.47%.     

CIS thin film solar cells with evaporated InSe buffer layers

This paper describes the investigations of CIS-based solar cells with a new In_xSe_y (IS) buffer layer. Studies were concentrated on determining the deposition conditions to get In_xSe_y thin films with adequate properties to be used in substitution of the CdS buffer layer, usually employed in the fabrication of this type of devices. Before the solar cell fabrication, the buffer layers grown by evaporation of the In₂Se₃ compound were characterized through transmittance and X-ray diffraction measurements. It was found that good results can be obtained using indium selenide film as the buffer layer, grown in the In₂Se₃ phase.Solar cells with structure Mo/CIS/In₂Se₃/ZnO were fabricated. The ZnO layer was deposited by reactive evaporation and the absorber CIS layer was grown on Mo by a two-stage process. The preliminary results obtained with this type of solar cells are J_sc=30.8 mA/cm², V_oc=0.445 V, FF≈0.6 and η=8.3% with an irradiance of 100 mW/cm². Solar cells fabricated using a CdS buffer layer deposited by CBD on CIS substrate, prepared under the same conditions used in the fabrication of Mo/CIS/In₂Se₃/ZnO cells, gave the following results: V_oc=0.43 V, J_sc=34 mA/cm², FF≈0.63 and η=9.2%.     

The electro-optical properties of amorphous indium tin oxide films prepared at room temperature by pulsed laser deposition

The electrical and optical properties of pulsed laser deposited amorphous indium tin oxide films at room temperature are discussed. The films were grown from indium oxide (In₂O₃) targets of different tin (Sn) doping content (0, 5 and 10 wt%) at different oxygen pressures (P_O2) ranging from 1×10⁻³ to 5×10⁻² Torr. The electrical and optical properties of the films were examined by Hall measurements and optical spectrophotometry. It was found that high conductivity amorphous films could be prepared at room temperature irrespective of the Sn doping content. The properties of these films deposited from 0, 5, 10 wt% Sn-doped In₂O₃ targets show a similar response to changes in P_O2. The maximal conductivity of (4.0, 2.1 and 1.8)×10³ S/cm and optical transmittance (visible) higher than 90% were obtained at P_O2 region of (1–1.5)×10⁻² Torr. An undoped In₂O₃ film produced the highest conductivity of 4×10³ S/cm in these studies.     

Photovoltaic properties of SnS based solar cells

Polycrystalline thin films of tin sulphide have been synthesised using spray pyrolysis. The layers grown at a temperature of 350 °C had the orthorhombic crystal structure with a strong (1 1 1) preferred orientation. The films had resistivities 30 Ω cm with an optical energy band gap (E_g) of 1.32 eV. Heterojunction solar cells were fabricated using sprayed SnS as the absorber layer and indium doped cadmium sulphide as the window layer and the devices were characterised to evaluate the junction properties as well as the solar cell performance. The current transport across the junction has been modelled as a combination of tunnelling and recombination. The best devices had solar conversion efficiencies of 1.3% with a quantum efficiency of 70%.     

Pyrite (FeS2) thin films prepared by spray method using FeSO4 and (NH4)2Sx

A simple spray method for the preparation of pyrite (FeS₂) thin films has been studied using FeSO₄ and (NH₄)₂S_x as precursors for Fe and S, respectively. Aqueous solutions of these precursors are sprayed alternately onto a substrate heated up to 120°C. Although Fe–S compounds including pyrite are formed on the substrate by the spraying, sulfurization of deposited films is needed to convert other phases such as FeS or marcasite into pyrite. A single-phase pyrite film is obtained after the sulfurization in a H₂S atmosphere at around 500°C for 30 min. All pyrite films prepared show p-type conduction. They have a carrier concentration (p) in the range 10¹⁶–10²⁰ cm⁻³ and a Hall mobility (μ_H) in the range 200–1 cm²/V s. The best electrical properties (p=7×10¹⁶ cm⁻³, μ_H=210 cm²/V s) for a pyrite film prepared here show the excellence of this method. The use of a lower concentration FeSO₄ solution is found to enhance grain growth of pyrite crystals and also to improve electrical properties of pyrite films.     

Triple-axis X-ray reciprocal space mapping of InyGa1−yAs thermophotovoltaic diodes grown on (1 0 0) InP substrates

Analysis of the composition, strain-relaxation, layer-tilt, and the crystalline quality of In_yGa_1−yAs/InP_1−xAs_x thermophotovoltaic (TPV) diodes grown by metal-organic vapor phase epitaxy (MOVPE) is demonstrated using triple-axis X-ray reciprocal space mapping techniques. In_0.53Ga_0.47As (E_gap=0.74 eV) n/p junction diodes are grown lattice matched (LM) to InP substrates and lattice-mismatched (LMM) In_0.67Ga_0.33As (E_gap=0.6 eV) TPV diodes are grown on three-step InP_1−xAs_x (0<x<0.32) buffer layers on InP substrates. X-ray reciprocal space maps about the symmetric (4 0 0) and asymmetric (5 3 3) reciprocal lattice points (RELPs) determine the in-plane and out-of-plane lattice parameters and strain of the In_yGa_1−yAs TPV active layer and underlying InP_1−xAs_x buffers. Triple-axis X-ray rocking curves about the LMM In_0.67Ga_0.33As RELP show an order of magnitude increase of its full-width at half-maximum (FWHM) compared to that from the LM In_0.53Ga_0.47As (250 vs. 30 arcsec). Despite the significant RELP broadening, the photovoltaic figure of merits show that the electronic quality of the LMM In_0.67Ga_0.33As approaches that of the LM diode material. This indicates that misfit-related crystalline imperfections are not dominating the photovoltaic response of the optimized LMM In_0.67Ga_0.33As material compared with the intrinsic recombination processes and/or recombination through native point defects, which would be present in both LMM and LM diode material. However, additional RELP broadening in non-optimized LMM In_0.67Ga_0.33As n/p junction diodes does correspond to significant degradation of TPV diode open-circuit voltage and minority carrier lifetime demonstrating that there is correlation between X-ray FWHM and the electronic performance of the LMM TPV diodes.     

Structural stability of chemically delithiated layered (1 − z)Li[Li1/3Mn2/3]O2–zLi[Mn0.5−yNi0.5−yCo2y]O2 solid solution cathodes

Lithium has been chemically extracted from the layered oxide solid solutions Li[Li_1/3Mn_2/3]O₂–(z)Li[Mn_0.5−yNi_0.5−yCo_2y]O₂ (0 ≤ y ≤ 1/2 and 0.25 ≤ z ≤ 0.75) and characterized by X-ray diffraction. The weak super lattice reflections that occur in the parent samples at around 2θ = 20–25° vanish on extracting a significant amount of lithium due to the removal of lithium from the transition metal layer and a consequent loss of the ordering between the Li⁺ and the transition metal ions. Additionally, the chemical delithiation process results in an incorporation of some protons from the chemical delithiation medium into the layered lattice, which has an influence on the structure of the delithiated samples. While the incorporation of a higher concentration (0.4 per formula unit) of protons results in the formation of O1 or P3 phases, delithiated samples with <0.2 protons maintain the initial O3 structure. However, the electrochemically charged samples maintain the initial O3 structure.     

An amorphous LiCo1/3Mn1/3Ni1/3O2 thin film deposited on NASICON-type electrolyte for all-solid-state Li-ion batteries

Amorphous LiCo_1/3Mn_1/3Ni_1/3O₂ thin films were deposited on the NASICON-type Li-ion conducting glass ceramics, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATSP), by radio frequency (RF) magnetron sputtering below 130 °C. The amorphous films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The Li/PEO₁₈-Li(CF₃SO₂)₂N/LATSP/LiCo_1/3Mn_1/3Ni_1/3O₂/Au all-solid-state cells were fabricated to investigate the electrochemical performance of the amorphous films. It was found that the low-temperature deposited amorphous cathode film shows a high discharge voltage and a high discharge capacity of around 130 mAh g⁻¹.     

New trends to grow the n-CdZn (S1−xSex)2/p-CuIn(S1−xSex)2 heterojunction thin films for solar cell applications

The n-CdZn(S_1−xSe_x) and p-CuIn(S_1−xSe_x)₂ thin films have been grown by the solution growth technique (SGT) on glass substrates. Also the heterojunction (p–n) based on n-CdZn (S_1−xSe_x)₂ and p-CuIn (S_1−xSe_x)₂ thin films fabricated by same technique. The n-CdZn(S_1−xSe_x)₂ thin film has been used as a window material which reduced the lattice mismatch problem at the junction with CuIn (S_1−xSe_x)₂ thin film as an absorber layer for stable solar cell preparation. Elemental analysis of the n-CdZn (S_1−xSe_x)₂ and p-CuIn(S_1−xSe_x)₂ thin films was confirmed by energy-dispersive analysis of X-ray (EDAX). The structural and optical properties were changed with respect to composition ‘x’ values. The best results of these parameters were obtained at x=0.5 composition. The uniform morphology of each film as well as the continuous smooth thickness deposition onto the glass substrates was confirmed by SEM study. The optical band gaps were determined from transmittance spectra in the range of 350–1000 nm. These values are 1.22 and 2.39 eV for CuIn(S_0.5Se_0.5)₂ and CdZn(S_0.5Se_0.5)₂ thin films, respectively. J–V characteristic was measured for the n-CdZn(S_1−xSe_x)₂/p-CuIn(S_1−xSe_x)₂ heterojunction thin films under light illumination. The device parameters V_oc=474.4 mV, J_sc=13.21 mA/cm², FF=47.8% and η=3.5% under an illumination of 85 mW/cm² on a cell active area of 1 cm² have been calculated for solar cell fabrication. The J–V characteristic of the device under dark condition was also studied and the ideality factor was calculated which is equal to 1.9 for n-CdZn(S_0.5Se_0.5)₂/p-CuIn(S_0.5Se_0.5)₂ heterojunction thin films.     

Photoelectrochemical properties of AgInS2 thin films prepared using electrodeposition

Ternary silver-indium-sulfide samples were deposited on fluorine-doped tin oxide (FTO) coated glass substrates using a one-step electrodeposition method. A new procedure for the deposition of AgInS₂ samples is reported. The effect of the [Ag]/[In] molar ratio in solution bath on the structural, morphological, and photoelectrochemical properties of samples was examined. X-ray diffraction patterns of samples show that the films are the AgInS₂ phase. The thickness, direct band gap, and indirect band gap of the films were in the ranges 209-1021 nm, 1.82-1.85 eV, and 1.44-1.51 eV, respectively. The carrier densities and flat-band potentials of films obtained from Mott-Schottky and open-circuit potential measurements were in the ranges of 4.2×10¹⁹-9.5×10¹⁹ cm⁻³ and −0.736 to −0.946 V vs. the normal hydrogen electrode (NHE), respectively. It was found that the samples with molar ratio [Ag]/[In]=0.8 in solution bath had a maximum photocurrent density of 9.28 mA/cm² with an applied bias of +1.0 V vs. an Ag/AgCl electrode in contact with electrolyte containing 0.25 M K₂SO₃ and 0.35 M Na₂S. The results show that high-quality AgInS₂ films can be deposited on FTO-coated glass substrates for photoelectrochemical (PEC) applications.