Sb2S3:C/CdS p-n junction by laser irradiation

In this paper, we report laser irradiated carbon doping of Sb₂S₃ thin films and formation of a p-n junction photovoltaic structure using these films. A very thin carbon layer was evaporated on to chemical bath deposited Sb₂S₃ thin films of approximately 0.5 μm in thickness. Sb₂S₃ thin films were prepared from a solution containing SbCl₃ and Na₂S₂O₃ at 27 °C for 5 h and the films obtained were highly resistive. These C/Sb₂S₃ thin films were irradiated by an expanded laser beam of diameter approximately 0.5 cm (5 W power, 532 nm Verdi laser), for 2 min at ambient atmosphere. Morphology and composition of these films were analyzed. These films showed p-type conductivity due to carbon diffusion (Sb₂ S₃:C) by the thermal energy generated by the absorption of laser radiation. In addition, these thin films were incorporated in a photovoltaic structure Ag/Sb₂S₃:C/CdS/ITO/Glass. For this, CdS thin film of 50 nm in thickness was deposited on a commercially available ITO coated glass substrate from a chemical bath containing CdCl₂, sodium citrate, NH₄OH and thiourea at 70 °C. On the CdS film, Sb₂S₃/C layers were deposited. This multilayer structure was subjected to the laser irradiation, C/Sb₂S₃ side facing the beam. The p-n junction formed by p-Sb₂S₃:C and n-type CdS showed V_oc = 500 mV and J_sc = 0.5 mA/cm² under illumination by a tungsten halogen lamp. This work opens up a new method to produce solar cell structures by laser assisted material processing.     

Cu(In,Ga)Se2 films prepared by sputtering with a chalcopyrite Cu(In,Ga)Se2 quaternary alloy and In targets

This study reports the successful preparation of Cu(In,Ga)Se₂ (CIGS) thin film solar cells by magnetron sputtering with a chalcopyrite CIGS quaternary alloy target. Bi-layer Mo films were deposited onto soda lime glass. A CIGS quaternary alloy target was used in combination with a stack indium target for compensating the loss of indium during annealing process. A one-stage annealing process was performed to form CIGS chalcopyrite phase. Experimental results show that the optimal adhesion strength, residual stress, and resistivity were obtained at a thickness ratio of 67% of bi-layer Mo films and a working pressure of 0.13 Pa. The CIGS precursor was layered through selenization at 798 K for 20 min. The stoichiometry ratios of the CIGS film were Cu/(In + Ga) = 0.91 and Ga/(In + Ga) = 0.23, which approached the device-quality stoichiometry ratio (Cu/(In + Ga) <0.95, and Ga/(In + Ga) <0.3). The resistivity of the sample was 11.8 Ωcm, with a carrier concentration of 3.6 × 10¹⁷ cm⁻³ and mobility of 1.45 cm²V⁻¹s⁻¹. The resulting film exhibited p-type conductivity.     

Gold-titania nanocomposite films with a periodic 3D nanostructure

In this study, we synthesized gold-titania nanocomposite thin films by using mesoporous titania thin films formed on indium tin oxide substrates as templates. The pore structure of our mesoporous titania thin films can be described as a periodic 3D pore network by interconnecting 7 nm sized cages. Electrochemical deposition of gold into the pores led to gold-titania nanocomposite films. Both gold and titania form continuous 3D network structures with internal periodicity. Because of the low conductivity of indium tin oxide substrate, the deposited gold formed isotropic islands. The absorption spectrum of the resultant gold-titania nanocomposite thin films showed two peaks, one at 640 nm and the other over a broad range of wavelengths longer than 1500 nm. These peaks grow with the increase of the deposition time but do not change the positions. The optical properties were explained in terms of the unique nanostructure of our gold-titania nanocomposite film.     

Effects of hydrogen in working gas for sputter-deposition on surface morphology and microstructure of indium tin oxide thin films grown at room temperature

Surface morphology and microstructure of indium tin oxide (ITO) thin films sputter deposited without heat treatment were obviously different from each other depending on the hydrogen concentration [H] in the working gas. The film surface became smoother with increasing [H] to 1%, but nucleation and growth of grains were apparent above [H] = 1.5%. The width of columnar grains in the ≤200 nm-thick films narrowed from ≈100 nm to ≈50 nm with increasing [H] from 0% to 1.5%. Randomly oriented and agglomerated grains were observed for the film deposited with [H] = 3.6%. Hydrogen added to the working gas induced reduction of the grain size, and then resulted in lowering of the carrier mobility.     

Influence of substrate temperature on structural,optical, and electrical properties of flash evaporated CuIn0.81Al0.19Se2 thin films

Chalcopyrite copper indium aluminum diselenide (CuIn_0.81Al_0.19Se₂) compound is prepared by direct reaction of high purity elemental copper, indium, aluminum and selenium in their stoichiometric proportion. Structural and compositional characterizations of pulverized material confirm the formation of a single phase, polycrystalline nature. CuInAlSe₂ (CIAS) thin films are deposited on organically cleaned soda lime glass substrates using flash evaporation technique by varying the substrate temperatures in the range from 423 K to 573 K. Influence of substrate temperature observed by X-ray diffraction (XRD), scanning electron microscope (SEM), optical and electrical measurement. CIAS Films grown at different substrate temperatures are polycrystalline in nature, exhibiting a chalcopyrite structure with lattice parameters a = ∼0.576 nm and c = ∼1.151 nm. The crystallinity in the films increases with increasing substrate temperature up to 473 K, and tend to degrade at higher substrate temperatures. Optical band gap is in the range of 1.20 eV–1.38 eV and the absorption coefficient is close to 10⁵ cm⁻¹. Electrical characterization reveals p-type conductivity and the structural, morphological and optical properties indicate potential use of CIAS thin films as an absorber layer for thin film solar cell applications.     

Solar cells with Sb2S3 absorber films

CdS/Sb₂S₃/PbS structures were prepared by sequential chemical deposition of CdS, Sb₂S₃ and PbS thin films on TEC-8 (Pilkington) transparent electrically conductive SnO₂ (TCO) coatings. CdS thin films (100 nm) were deposited with hexagonal structure from Cd-citrate bath and of cubic structure from Cd-ammine/triethanolamine bath. Sb₂S₃ thin films were deposited at 40 °C from a solution mixture of potassium antimony tartrate, triethanolamine, ammonia and thioacetamide(TA) or at 1 to 10 °C from a mixture of antimony trichloride and thiosulfate (TS). These films were made photoconductive by heating at temperatures 250 to 300 °C. When heated in the presence of a chemically deposited Se thin film of 300 nm, a solid solution Sb₂S_1.8Se_1.2 resulted. PbS thin films of 100-200 nm thickness were deposited on the TCO/CdS/Sb₂S₃ or TCO/CdS/Sb₂S_1.8Se_1.2 structure. Graphite paint was applied on the PbS film prior to applying a silver epoxy paint. The cell structures were of area 0.4 cm². The best results reported here is for a cell: TCO/CdS(hex-100 nm)/Sb₂S₃(TS-100 nm)/PbS(200 nm) with open circuit voltage (V_oc) 640 mV, short circuit current density 3.73 mA/cm², fill factor 0.29, and conversion efficiency 0.7% under 1000 Wm^− 2 sunlight. Four series-connected cells of area 1 cm² each gave V_oc of 2 V and short circuit current of 1.15 mA.     

Nanocrystalline ITO-Sn2S3 transparent thin films for photoconductive sensor applications

Nanocrystalline indium tin oxide (ITO) film containing 5 wt% Sn was prepared on glass substrate by the spray pyrolysis technique at a substrate temperature of 500 °C. In order to enhance the photosensitivity of ITO, thiourea (CS(NH₂)₂ was added to the precursor to obtain the [S]/[In] proportion of 0.1, 0.2, 0.4 and 0.6. The X-ray diffraction patterns showed that beside the bixbyite structure of ITO, the characteristic peaks corresponding to Sn₂S₃ appeared in XRD profiles recorded for the films with [S]/[In] = 0.1 and 0.2. In addition, sulfur additive caused a considerable decline in crystallinity quality. The optical properties of the films were studied using transmittance measurements in the wavelength range 300–1,000 nm. As a result, ITO and ITO-Sn₂S₃ thin films were prepared with resistivity of 3.06–3.7 × 10^?4 Ω cm and a transmittance of 88–91 % at the wavelength of 550 nm. Moreover, the electrical resistances of ITO and ITO-Sn₂S₃ films as a function of time were measured in darkness and under illumination of light in the visible range. The photoresistance results revealed that the ITO-Sn₂S₃ film with [S]/[In] = 0.2 was efficiently sensitive to visible light for photoconductive sensor applications, besides being high conductive and transparent.     

Effect of oxygen partial pressure on electrical characteristics of amorphous indium gallium zinc oxide thin-film transistors fabricated by thermal annealing

We report the fabrication and electrical characteristics of high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a polymer gate dielectric prepared by spin coating on a glass substrate at different oxygen partial pressure values. The transmittance of the deposited polymer film was greater than 90% at 600 nm a-IGZO thin films were deposited on glass substrates using RF magnetron sputtering at different oxygen partial pressure values. The a-IGZO TFTs were prepared by rapid thermal annealing at 350 °C for 10 min at a 0.2% oxygen partial pressure. It was observed that a-IGZO TFTs with an active channel layer exhibited enhanced mode operation, a threshold voltage of 1 V, an on-off current ratio of 10³, and a field-effect mobility of 18 cm²/Vs.     

Effect of oxygen partial pressure on electrical characteristics of amorphous indium gallium zinc oxide thin-film transistors fabricated by thermal annealing

We report the fabrication and electrical characteristics of high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with a polymer gate dielectric prepared by spin coating on a glass substrate at different oxygen partial pressure values. The transmittance of the deposited polymer film was greater than 90% at 600 nm a-IGZO thin films were deposited on glass substrates using RF magnetron sputtering at different oxygen partial pressure values. The a-IGZO TFTs were prepared by rapid thermal annealing at 350 °C for 10 min at a 0.2% oxygen partial pressure. It was observed that a-IGZO TFTs with an active channel layer exhibited enhanced mode operation, a threshold voltage of 1 V, an on-off current ratio of 10³, and a field-effect mobility of 18 cm²/Vs.     

Compositional dependence of the optical parameters for Bi5GexSe65−x (30 ≤ x ≤ 45) films

Different compositions of Bi₅Ge_xSe_95−x (x = 30, 35, 40 and 45 at %) thin films were deposited onto cleaned glass substrates by thermal evaporation method. The structural characterization revealed that, the as-prepared films of x = 30, 35 and 40 at. % are in amorphous state but there are few tiny crystalline peaks of relatively low intensity for the film with x = 45 at. %. The chemical composition of the as-prepared Bi₅Ge_xSe_65−x films has been checked using energy dispersive X-ray spectroscopy (EDX). The optical properties for the as-deposited Bi₅Ge_xSe_65−x thin films have been studied. The additions of Ge content were found to affect the optical constants (refractive index, n and the extinction coefficient, k). Tauc’s relation for the allowed indirect transition is successfully describing the mechanism of the optical absorption. It was found that, the optical energy gap (E_g) decreases with the increase in Ge content. These obtained results were discussed in terms of the chemical bond approach proposed by Bicermo and Ovshinsky. The composition dependence of the refractive index was discussed in terms of the single oscillator model.     

Indium sulfide buffer/CIGSSe interface engineering: Improved cell performance by the addition of zinc sulfide

Indium sulfide buffer layers deposited by the spray-ion layer gas reaction (Spray-ILGAR) technique are a viable alternative to the traditional cadmium sulfide buffer layer in thin film solar cells. In the present work we report on the results of manipulating the absorber/buffer interface between the chalcopyrite Cu(In,Ga)(S,Se)₂ absorber (CIGSSe) and the indium sulfide buffer. It is shown that the deposition of a small amount of zinc sulfide at the absorber/buffer interface can be used to increase the open circuit voltage. A small but significant increase of 20 mV (up to 580 mV), as compared to the pure indium sulfide buffered cells is possible leading to an increase in the overall efficiency.     

Optical and electrical properties of p-type AgInSnxS2−x (x = 0–0.04) thin films prepared by spray pyrolysis

AgInSn_xS_2−x (x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS₂. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn_xS_2−x (x < 0.2) resemble those of chalcopyrite AgInS₂. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn_xS_2−x (x < 2) thin films.     

Effect of the [Al/Zn] ratio in the starting solution and deposition temperature on the physical properties of sprayed ZnO:Al thin films

Aluminum-doped zinc oxide thin films (ZnO:Al) were deposited on sodocalcic glass substrates by the chemical spray technique, using zinc acetate and aluminum pentanedionate as precursors. The effect of the [Al/Zn] ratio in the starting solution, as well as the substrate temperature, on the physical characteristic of ZnO:Al thin films was analyzed. We have found that the addition of Al to the starting solution decreases the electrical resistivity of the films until a minimum value, located between 2 and 3 at.%; a further increase in the [Al/Zn] ratio leads to an increase in the resistivity. A similar resistivity tendency with the substrate temperature was encountered, namely, as the substrate temperature is increased, a minimum value of around 475 °C in almost all the cases, was obtained. At higher deposition temperatures the film resistivity suffers an increase. After a vacuum-thermal treatment, performed at 400 °C for 1 h, the films showed a resistivity decrease about one order of magnitude, reaching a minimum value, for the films deposited at 475 °C, of 4.3 × 10^− 3 Ω cm.The film morphology is strongly affected by the [Al/Zn] ratio in the starting solution. X-ray analysis shows a (002) preferential growth in all the films. As the substrate temperature increases it is observed a slight increase in the transmittance as well as a shift in the band gap of the ZnO:Al thin films.     

Preparation and characterization of Cu–In–S thin films by electrodeposition

In this paper, we report the preparation and characterization of Cu–In–S thin films on stainless steel prepared by electrodeposition technique. The electrolytic bath used for preparation of the thin films consists of metal salts dissolved in a buffer solution. This buffer solution can control the formation and composition of thin films. In order to get adequate crystalline of CuInS₂ thin films, the as deposited films were annealed in N₂-atmosphere. Samples were characterized using X-ray diffraction (XRD), electron probe micro-analysis (EPMA), and scanning electron microscopy (SEM). The band-gap value of the material was estimated using optical transmittance and reflectance data on thin films deposited on commercial glass/indium tin oxide (ITO) substrates. It was found that the band-gap of the films is close to 1.5 eV.     

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.

     

Characterization of CuInS2 thin films for solar cells prepared by spray pyrolysis

We have made a study of the chemical composition, the electrical, the optical and the structural properties of polycrystalline CuInS₂ thin films prepared by spray pyrolysis to be used for thin film solar cells. These films were deposited starting from aqueous solutions with different chemical compositions ([Cu]/[In] and [S]/[Cu] ratios) and at different substrate temperatures. In all cases, the material is p-type with grains preferentially oriented in the (112) direction of the sphalerite structure. The electro-optical properties show a very strong dependence on the [Cu]/[In] ratio in the solution. Films with copper excess have smaller resistivity and better crystallinity than those which are stoichiometric or have indium excess. The results obtained in this work show the possibility of having CuInS₂ thin films with a wide range of resistivity, a fact that could be important for making solar cells based on this material.     

Nickel diffusion in polycrystalline CuInSe2 thin films with a <112> fiber texture

Nickel diffusion in CuInSe₂ thin films was studied in the temperature range 430-520 °C. Thin films of copper indium diselenide (CuInSe₂) were prepared by selenization of CuInSe₂-Cu-In multilayered structure on glass substrate. A thin film of Nickel was deposited and annealed at different temperatures. Surface morphologies of the Ni diffused and undiffused CuInSe2 films were investigated using scanning electron microscope. The alteration of Nickel concentration in the CuInSe₂ thin film was measured by Energy Dispersive X-Ray Fluorescence (EDXRF) technique. These measurements were fitted to a complementary error function solution and the diffusion coefficients at four different temperatures were evaluated. The diffusion coefficients of Ni in CuInSe₂ films were estimated from concentration profiles at temperatures 430-520 °C as D = 1.86 × 10^− 7(cm²s^− 1)exp[− 0.68(eV)/kT].     

Fabrication and characterization of CuInS2 films by chemical bath deposition in acid conditions

Non-crystalline copper indium disulphide (CuInS₂) thin films had been deposited on ITO glass by chemical bath deposition (CBD) in acid conditions. Then polycrystalline CuInS₂ films were obtained after sulfuration in sulfur atmosphere at 450 °C for 1.5 h. The films had been characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Raman scattering measurements and energy dispersive X-ray analysis (EDX). The optical and electrical property of the thin films was also measured. The results showed that the pure, flatness, and well crystallized CuInS₂ thin films with good electrical and optical property had been obtained, meaning that the chemical bath deposition in acid conditions is suitable for the deposition of CuInS₂ thin films.     

Finite element simulation and experimental research on ZnO:Al by magnetron sputtering

Aluminum doped zinc oxide (ZnO:Al) thin films are suitable for the use as transparent conductive electrode in copper indium gallium selenide Cu(In,Ga)Se₂ thin film solar cells. The resistivity and film quality of ZnO:Al deposited on soda lime glass is nonuniform in magnetron sputtering process. According to the measurement results of magnetic field on the top of the target, obvious magnetic field distribution nonuniformity is observed along the vertical and horizontal directions respectively. With the longer distance between target and substrate, the magnetic field intensity becomes lower and flatter between the two magnet poles. Based on the simulation results by finite element analysis, it is verified the nonuniformity of magnetic field distribution influences the probability of Ar⁺ particles collision and the deposition of zinc oxide (ZnO) particles in different regions on substrate. The higher resistivity of ZnO:Al films is obtained where the magnetic field intensity is stronger.     

Analysis of the absorption layer of CIGS solar cell by laser-induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) was applied for the elemental analysis of the thin copper indium gallium diselenide (CuIn(1-x)Ga(x)Se(2) [CIGS]) absorption layer deposited on Mo-coated soda-lime glass by the co-evaporation technique. The optimal laser and detection parameters for LIBS measurement of the CIGS absorption layer (1.23 μm) were investigated. The calibration results of Ga/In ratio with respect to the concentration ratios measured by x-ray fluorescence and inductively coupled plasma optical emission spectroscopy showed good linearity.