Investigations on copper zinc tin sulfide thin films grown through nebulizer assisted spray pyrolysis technique

An attempt is made in this work to synthesize the nontoxic Cu₂ZnSnS₄ (CZTS) thin film on FTO coated glass substrates through aerosol assisted nebulizer spray pyrolysis technique at different annealing temperatures for photovoltaic energy conversion. The deposited thin film is further used to form a heterojunction interface with a cadmium sulfide layer to fabricate a solar cell with Glass/FTO/CdS/CZTS/Ag superstrate structure to reveal its photovoltaic application. Various characterization techniques are utilized to study its inherent properties. X-ray diffraction (XRD) is employed to investigate the structural parameters such as crystallite size, microstrain and dislocation density which shows a preferential peak for (112) plane around 28.5° confirming the formation of kesterite CZTS. Raman measurements establish the peak for CZTS at 336 cm⁻¹ and confirm the absence of parasitic secondary phases for an excitation wavelength of 488 nm. Scanning electron microscope and atomic force microscope used to examine the surface morphology and roughness of the films reveal a good surface morphology with a grain size of 555.9 nm and roughness of 123.7 nm for an annealing temperature of 350°C. The bandgap of the deposited CZTS films is found to be around 1.5 eV. The I-V characteristics of CZTS seem to be better for the 350°C annealed film. The performance of the optimized CZTS absorber layer is tested by forming a solar cell structure. The devised solar cell exhibited an open circuit voltage of 213 mV and a short circuit current density of 490 μA cm⁻² with a conversion efficiency of 0.68% substantiating the usage of the prepared film as an absorber for photovoltaic conversion.     

Effects of ITO precursor thickness on transparent conductive Al doped ZnO film for solar cell applications

Al doped ZnO (AZO) film was continuously deposited on ITO precursor on glass substrate by d.c. magnetron sputtering. The thickness of ITO was varied from 30 to 120 nm in order to investigate the effect of ITO thickness on crystallinity of AZO film. X-ray diffraction measurement shows that AZO film grown on ITO has an enhanced (0 0 2) preferred orientation as the ITO thickness was increased. The crystalline structure improvement of AZO film with an increase of ITO precursor thickness is due to the near-epitaxial growth of AZO on ITO precursor. As the ITO thickness was increased, mobility of AZO film by the Hall measurement was significantly increased from 5.4 cm²/V s (no ITO) to 23.6 cm²/V s (ITO 120 nm), and resistivity was about 81.7% improved from 1.99×10⁻³ to 3.63×10⁻⁴ Ω cm. The AZO films with ITO revealed excellent average transmission of visible (90.0%) and NIR (89.6%) regions, whereas those of AZO film without ITO were 82.1% and 88.1%, respectively. The haze values of AZO film with ITO of 90 and 120 nm are similar or higher than those of AZO film without ITO. The surface textured AZO film with ITO precursor is promising for optoelectronic applications such as the front TCO of thin film solar cells.     

Cigs flexible nano solar cell by inert argon gas condensation

The Cu(In_0.7Ga_0.3)Se₂ nano solar cell pn junction structure consist of six layers of Al/CIGS/nano-CIGS/CdS/ITO/PET with thicknesses about 200, 500, 70, 100, 150 nm and 170 um were deposited by thermal evaporation technique at vacuum pressure 2 × 10^–5 mbar respectively. where the ITO/PET conductive flexible substrate with sheet resistance 15 Ohms per sq. The X-ray diffraction analysis showed that as-deposited thin films CIGS and CdS are polycrystalline where optical energy gap and carrier concentration are found that 1.15 and 2.38 eV with p = 3.58 × 10¹⁰ cm^–3 and n = 3.11 × 10¹³ cm^–3 respectively. CIGS nano solar cell thin films are deposited on CdS/ITO/PET with assistance of inlet Argon gas vacuum pressure at 1, 5, 20 mbar by thermal evaporation technique at room temperature by using Inert gas condensation (IGC) is the method by which one can deposit films with high purity as deposition is done in low vacuum. The high magnification SEM image of CIGS nano-structures synthesized at 20 mbar revealed that the particles have exact spherical shape with sizes ranged from few nanometers to hundreds nanometers due to agglomeration effect. It was found that the grain size and the root mean square of surface roughness increases as Argon gas pressure increase. Therefore the structure of CIGS thin films has been changed from polycrystalline to nanostructure and have been found with increase Argon gas vacuum pressure from 1mbar to 5 mbar and then 20 mbar will increase grain size at 2θ = 32° from 15.9, 18.9 and 25.7 nm with decrease optical energy gap from 1.54, 1.44 and 1.26 eV respectively. The results showed the efficiency increase from 1.37% of CIGS/CdS to 2.01% of CIGS nano thin films of solar cells.     

RF sputter deposition of the high-quality intrinsic and n-type ZnO window layers for Cu(In,Ga)Se2-based solar cell applications

Transparent ZnO films were prepared by rf magnetron sputtering, and their electrical, optical, and structural properties were investigated under various sputtering conditions. Aluminum-doped n-type(n-ZnO) and undoped intrinsic-ZnO (i-ZnO) layers were deposited on a glass substrate by incorporating different targets in the same reaction chamber. The n-ZnO films were strongly affected by argon ambient pressure and substrate temperature, and films deposited at 2 mTorr and 100°C showed superior properties in resistivity, transmission, and figure of merit (FOM). The sheet resistance of ZnO film was less dependent on film thickness when the substrate was heated during deposition. These positive effects of elevated substrate temperature are presumably attributed to the rearrangement of the sputtered atoms by the heat energy. Also, the films are electrically uniform through the 5 cm×5 cm substrate. The maximum deviation in sheet resistance is less than 10%. All of the films showed strong (0 0 2) diffraction peak near 2θ =34°. The undoped i-ZnO films deposited in the mixture of argon and oxygen gases showed high transmission properties in the visible range, independent of the Ar/O₂ ratio, while resistivity rose with increased oxygen partial pressure. The Cu(In,Ga)Se₂ solar cells, incorporating bi-layer ZnO films (n-ZnO/i-ZnO) as window layer, were finally fabricated. The fabricated solar cells showed 14.48% solar efficiency under AM 1.5 conditions (100 mW/cm²).     

Improved Jsc in CIGS thin film solar cells using a transparent conducting ZnO:B window layer

A comparative study of the cell performance of CIGS thin-film solar cells fabricated using ZnO:Al and ZnO:B window layers has been carried out. ZnO:B films were deposited by RF magnetron sputtering using an undoped ZnO target in a B₂H₆–Ar gas mixture. The short-circuit current (J_sc) was found to improve upon the replacement of the ZnO:Al layer with ZnO:B layers. This improvement in J_sc is attributed to an increase in quantum efficiency due to the higher optical transmission of the ZnO:B layer in the near-infrared region. The best cell fabricated with a MgF₂/ZnO:B/i-ZnO/CdS/CIGS/Mo structure yielded an active area efficiency of 18.0% with V_oc=0.645 V, J_sc=36.8 mA/cm², FF=0.76, and an active area of 0.2 cm² under AM 1.5 illumination.     

Improvement of structural and optoelectrical properties by post-deposition electron beam annealing of ITO thin films

Sn-doped In₂O₃ (ITO) thin films were deposited on a glass substrate with reactive RF magnetron sputtering and then post-deposition electro-annealed. The electron accelerating voltage was varied from 300 to 900 V, and the substrate temperature was increased to 250 °C with an electron accelerating voltage of 900 V for 20 min in a 4 × 10^?1 Pa vacuum. As-deposited and ITO films electro-annealed at low energy (≤600 eV) were found to be in the amorphous phase, while ITO films electro-annealed at 900 eV showed diffraction peaks of the ITO (222) and (400) planes. As the electron accelerating voltage increased, the electrical resistivity decreased to as low as 6 × 10^?4 Ωcm, and the mean optical transmittance also increased from 79 to 82% in the visible wavelengths. The electro-annealed films showed a higher figure of merit (1.8 × 10^?3 Ω^?1) than the as-deposited ITO films (6.7 × 10^?3 Ω^?1), indicating that electro-annealed ITO films have better optoelectrical performance than as-deposited films.     

Effect of ionic conductivity of a PVC–LiClO4 based solid polymeric electrolyte on the performance of solar cells of ITO/TiO2/PVC–LiClO4/graphite

This paper reports the effect of ionic conductivity of the solid polymeric electrolyte of polyvinylchloride–lithium perchlorate (PVC–LiClO₄) on the performance of a solar cell of ITO/TiO₂/PVC–LiClO₄/graphite. Titanium dioxide films have been used as a photoelectrochemical solar cells. The films were deposited onto a ITO-coated glass substrate by a screen printing technique. The electrolytes were prepared by solution casting. The ionic conductivity of the electrolytes was obtained with an impedance spectroscopy technique. ITO and graphite films were chosen as the front and counter electrode of the device, respectively. The graphite films were deposited onto a glass substrate by the electron-beam evaporation technique. The short-circuit current density and open-circuit voltage of the device were found to increase with increasing ionic conductivity of solid polymeric electrolyte of PVC–LiClO_4. The highest short-circuit current density and open-circuit voltage were 0.94 μA cm⁻² and 186 mV, respectively. The conversion efficiency was low.     

Irradiation-induced modifications and PEC response - A case study of SrTiO3 thin films irradiated by 120 MeV Ag ions

This paper deals with a study on the effect of 120 MeV Ag⁹⁺ ion irradiation on photoelectrochemical properties of SrTiO₃ thin films deposited on Indium doped Tin Oxide (ITO) coated glass by sol-gel spin-coating technique. The structural evolution in the pristine and irradiated films was determined by X-ray diffraction and X-ray photoelectron spectroscopy. Surface morphology was studied by Atomic Force Microscopy (AFM) and optical measurements were done by UV-visible absorption spectroscopy. Irradiation of SrTiO₃ thin films was found to be effective in improving its photoelectrochemical properties. A noticeable decrease in the average grain diameter from 36 to 26 nm, reduction in bandgap from 3.55 to 3.43 eV and increase in roughness after irradiation contributed in enhancing photoelectrochemical activity of SrTiO₃ thin films. Thin films irradiated at fluence 3 × 10¹² ions cm⁻², when used in PEC cell exhibited enhanced photocurrent of 0.16 mA cm⁻² at zero bias conditions, which was four times higher than that of the unirradiated sample.     

Structural, optical and photoelectrochemical studies of the cadmium sulphide films grown by chemical bath deposition

Cadmium sulphide films have been grown by chemical bath deposition using an aqueous medium. Growth rate has been studied on the basis of the film thickness variation with deposition period. Structural investigation using XRD has shown the presence of polycrystalline deposits of wurtzite structure. The optical absorbance has revealed that the band gap of the CdS layers has been 2.39 eV. The CdS films have been employed in electrochemical photovoltaic cells of configuration glass/ITO/CdS//S₂S²⁻₂//Ni to test their photoactivity. The solar cell parameters have been correlated with the growth parameters.     

Studies on the interface between novel type ZnO and p-a-SiC:H in 1.5 eV a-SiGe:H pin diodes in comparison to SnOx and ITO

1.5 eV a-SiGe:H pin diodes with p-a-SiC:H window layers (E_g = 1.95 eV) have been deposited on conventional ITO, SnO_x and novel Al-doped ZnO (ZnO:Al) transparent conductive oxides (TCO) in order to compare the influence of TCO/p-a-SiC:H interfaces on diode parameters. Characterization by transmission, sheet resistance and SEM photographs reveals comparable features for the three types of TCOs, ZnO:Al additionally shows a very high chemical stability in hydrogen containing plasmas. Transmission and adsorption experiments also were performed on the layer-system TCO + thin p-a-SiC:H indicating different growth rates of p-a-SiC:H on ZnO:Al and SnO_x. SCLC experiments on sandwich structures consisting of TCO/n⁺ in⁺/Cr demonstrate an increase in the midgap defect density of states N_t(E) for a-SiGe:H layers on ITO but no dependence of N_t(E) on the crystallite size of the substrates. In the case of ZnO:Al the analysis of I–V characteristics underAM1 illumination (100 mW/cm²) displays a clear improvement of open-circuit voltage V_oc and short-circuit current density I_sc. This is due to a higher work function of ZnO:Al in comparison to SnO_x and, therefore, increased built-in potential V_bi. Diffusion of Zn and In into the p-a-SiC:H-layer, however, causes a rise in series resistance R_S and lowering of the fillfactor FF for ZnO:Al and ITO as front contacts. With respect to extended optimization, in particular avoidance of the high series resistance, the very stable, high temperature deposited ZnO:Al seems to be a promising material for a-Si:H based solar cells.     

Optoelectronic properties of chemically deposited Bi2S3 thin films and the photovoltaic performance of Bi2S3/P3OT solar cells

Thin films of bismuth sulfide (Bi₂S₃), prepared on conductive tin-doped indium oxide (ITO)-glass substrates by chemical deposition showed a variation of optical band gap with thickness: 1.8 eV for a 50 nm film (deposited at 40 °C for 30 min) to 1.5 eV for a 200 nm film deposited for 2 h. The electronegativity for Bi₂S₃ compound is 5.3 eV, as estimated from the ionization energy and electron affinity of elemental Bi and S, and thus the electron affinity of chemically deposited Bi₂S₃ film was deduced to be 4.5 eV. In the energy level analysis of ITO/Bi₂S₃/P3OT/Au structure, Bi₂S₃ was established as an electron acceptor. To produce ITO/Bi₂S₃/P3OT/Au solar cell structures, poly3-octylthiophene (P3OT), prepared in the laboratory was dissolved in toluene and was drop-cast on the Bi₂S₃ film and a gold film was thermally evaporated. Under 100 mW/cm² tungsten-halogen irradiation incident from the ITO-side, the cell using a Bi₂S₃ film with thickness of 50 nm has the highest open circuit voltage (V_oc) of 440 mV and short-circuit current density (J_sc) of 0.022 mA/cm². The addition of a CdS thin film (90 nm) between ITO and B₂S₃ would increase V_oc to 480 mV, and J_sc to 0.035 mA/cm². The role of surface morphology and optoelectronic properties of the Bi₂S₃ film in the photovoltaic performance of the junction is discussed.     

Optical and electrochromic properties of oxygen sputtered tungsten oxide (WO3) thin films

Thin films of tungsten oxide (WO₃) were deposited onto glass, ITO coated glass and silicon substrates by pulsed DC magnetron sputtering (in active arc suppression mode) of tungsten metal with pure oxygen as sputter gas. The films were deposited at various oxygen pressures in the range 1.5×10⁻²−5.2×10⁻² mbar. The influence of oxygen sputters gas pressure on the structural, optical and electrochromic properties of the WO₃ thin films has been investigated. All the films grown at various oxygen pressures were found to be amorphous and near stoichiometric. A high refractive index of 2.1 (at λ=550 nm) was obtained for the film deposited at a sputtering pressure of 5.2×10⁻² mbar and it decreases at lower oxygen sputter pressure. The maximum optical band gap of 3.14 eV was obtained for the film deposited at 3.1×10⁻² mbar, and it decreases with increasing sputter pressure. The decrease in band gap and increase in refractive index for the films deposited at 5.2×10⁻² mbar is attributed to the densification of films due to ‘negative ion effects’ in sputter deposition of highly oxygenated targets. The electrochromic studies were performed by protonic intercalation/de-intercalation in the films using 0.5 M HCl dissolved in distilled water as electrolyte. The films deposited at high oxygen pressure are found to exhibit better electrochromic properties with high optical modulation (75%), high coloration efficiency (CE) (141.0 cm²/C) and less switching time at λ=550 nm; the enhanced electrochromism in these films is attributed to their low film density, smaller particle size and larger thickness. However, the faster color/bleach dynamics is these films is ascribed to the large insertion/removal of protons, as evident from the contact potential measurements (CPD) using Kelvin probe. The work function of the films deposited at 1.5 and 5.2×10⁻² mbar are 4.41 and 4.30 eV, respectively.     

THE INFLUENCE OF DEPOSITION AND PROCESSING CONDITIONS ON THE PROPERTIES OF EVAPORATED CdTe/ CdS LAYERS AND SOLAR CELLS

The influence of the deposition and CdCl₂ doping conditions on the properties of CdTe layers and on the performance of CdTe/CdS/ITO/glass solar cells is reported. Relatively high deposition temperatures (300-350°C) were found to enhance the reproducibility of the optical quality of the CdTe. Oxidation of CdTe layers during air annealing was observed and monitored by XRD. Conventional wet dip and CdCl₂ vapour doping of CdTe are compared. Methods for reducing the incidence of pinholes in the CdTe are described, the junction uniformity having been monitored by EBIC. The best solar cell made in this work had an efficiency of 9.87%. (V _oc = 0.696V, J _sc = 24.1 mA/cm², FF = 59%).     

Photoelectrochemical study of screen-printed cadmium sulphide electrodes

Thin films of CdS have been prepared by the screen-printing technique. Optical absorption studies reveal a band gap of 2.42 eV. Current-voltage studies at the CdS-(1 M NaOH-0.1 M Na₂S-0.1 M S) interface yield an exchange current density of 6 X 10⁻⁶ A CM⁻² and a junction ideality factor of 2.8. Mott-Schottky plots at 0.4, 1.0, 2.0 and 4.0 kHz show a flat-band potential of -1.07 V (SCE). At 84.5 mW cm⁻² tungsten-halogen illumination, the photoelectrochemical cell gives an open-circuit voltage of 0.32 V, a short-circuit current density of 0.23 mA cm⁻², and a fill-factor of 0.42.     

Composition, surface topography, structure, Raman, and electrochemical/photoelectrochemical characterisation of CdxHg1−xTe films

Cd-rich Cd_xHg_{1 − x}Te films have been electrodeposited under potentiostatic conditions on conducting glass and Ti substrates from an acidic solution containing the respective ions as Cd²⁺:Hg²⁺:HTeO₂⁺ = 100:1:2. Six films one after another have been prepared from a single electrochemical cell. EDAX analysis of the air annealed films show decreasing Hg content in the deposit as the number of film preparation increases. SEM analysis indicate undulatory surface with Hg-rich clusters at the top surface. XRD analysis indicate the presence of Cd_xHg_{1 − x}Te along with . The Cd_xHg_{1 − x}Te alloy formation have been confirmed from Raman shift measurements which change with composition, x. The as-deposited films are n-type but converts to p-type after air annealing. Spectral response measurements gave band gap values that change with Hg content in the deposit. Band gap values ranging from 1.1 eV to 1.45 eV have been estimated. Photoelectrochemical solar cells using polysulphide electrolyte have been fabricated which gave an open-circuit photovoltage and short-circuit photocurrent, respectively, as 325 mV and 5.5 mA/cm² under 60 mW/cm² intensity of illumination.     

Synthesis and electro-optic properties of nanosized-boron doped cadmium oxide thin films for solar cell applications

Boron doped CdO thin films were prepared by sol–gel dip coating technique. Atomic force microscopy results indicate that the boron doped CdO films have the nanostructure. The influence of the boron doping on the film growth is resulted in a change of grain size. The optical band gap of the CdO films was significantly changed by boron dopant. The refractive index dispersion of the films obeys the single oscillator model. The dispersion parameters, oscillator and dispersion energy were changed by boron dopant. The optical absorption results show that the optical band gap of the CdO film can be engineered over a wide range of 2.27–2.45 eV by introducing B dopant. For solar cell applications of the CdO film, a p-Si/1% B doped n-CdO heterojunction solar cell was fabricated and the solar cell shows the best values of open circuit voltage, V_oc = 0.37 and short circuit current density, J_sc = 0.81 mA/cm² under AM1.5 illumination, despite the fact that V_oc and J_sc are lower than those reported in the literature without using frontal grid contacts and or post-deposition annealing. It is evaluated that this work is useful as a basis search for synthesis of the nanosized-boron doped cadmium oxide thin films for solar cell applications and more competitive p-Si/n-CdO based solar cells.     

Fabrication of wide-gap Cu(In1−xGax)Se2 thin film solar cells: a study on the correlation of cell performance with highly resistive i-ZnO layer thickness

The correlation of the cell performance of wide-gap Cu(In_1−xGa_x)Se₂ (CIGS) solar cells with the thickness of highly resistive i-ZnO layers, which are commonly introduced between the buffer layer and the transparent conductive oxide (TCO) layer in CIGS solar cell devices, was studied. It was found that cell parameters, in particular, the fill factor (F.F.) varied with the thickness of the i-ZnO layers and the variation of the F.F. was directly related to cell efficiency. A 16%-efficiency was achieved without use of an anti-reflection coating from wide-gap (E_g1.3 eV) CIGS solar cells by adjusting the deposition conditions of the i-ZnO layers.     

Effect of under nitrogen annealing on photo-electrochemical characteristics of films deposited from authentic Cu2SnSe3 sources by thermal vacuum under argon gas condensation

This communication describes how annealing under nitrogen affects photo-electrochemical characteristics of films deposited from authentic Cu₂SnSe₃ sources by vacuum evaporation under argon gas (low flow rate 5 cm³/min) using substrate 300 °C. Annealing lowered the photoresponse of the deposited film, by affecting crystallite structure, morphology, composition and pores in the films. Annealing at temperatures in the range 150–350 °C improved crystallinity of the film but lead to pore formation between adjacent, which lowered photoresponse by increased resistance across the electrode/redox interface. Higher temperature (450 °C) annealing lead to SnO₂ formation, as an additional phase, at the expense of Cu₂SnS₃ decomposition. Porosity and mixed phases with SnO₂ presumably increased film internal resistance and resulted in poor charge transfer across the solid/redox couple interface. By affecting film characteristics, annealing lowered photoresponse for the deposited films.     

Electrodeposited cuprous oxide on indium tin oxide for solar applications

Semiconducting cuprous oxide films were prepared by electrodeposition onto commercial conducting glass coated with indium tin oxide deposited by spraying technique. The cuprous oxide (Cu₂O) films were deposited using a galvanostatic method from an alkaline CuSO₄ bath containing lactic acid and sodium hydroxide at a temperature of 60°C. The film's thickness was about 4–6 μm. This paper includes discussion for Cu₂O films fabrication, scanning electron microscopy and X-ray diffractometry studies, optical properties and experimental results of solar cells. The values of the open circuit voltage V_oc of 340 mV and the short circuit current density I_sc of 245 μA/cm² for ITO/Cu₂O solar cell were obtained by depositing graphite paste on the rear of the Cu₂O layer. It should be stressed that these cells exhibited photovoltaic properties after heat treatment of the films for 3 h at 130°C. An electrodeposited layer of Cu₂O offers wider possibilites for application and production of low cost cells, both in metal–semiconductor and hetero-junction cell structures, hence the need to improve the photovoltaic properties of the cells.     

Cd0.5Zn0.5S/Ni2P noble-metal-free photocatalyst for high-efficient photocatalytic hydrogen production: Ni2P boosting separation of photocarriers

Establishing efficient co-catalytic loaded semiconductors for efficient charge separation is a hopeful way for enhance photocatalytic water splitting hydrogen evolution. Herein, we successfully constructed the Cd_0.5Zn_0.5S/Ni₂P (CZS/Ni₂P) nanocomposites via two-step hydrothermal method. The CZS/Ni₂P composites show much improved activity than the origin CZS for photocatalytic H₂ generation. When the content of Ni₂P loaded on the Cd_0.5Zn_0.5S (CZS) is 0.3 mol%, the photocatalyst achieves the highest photocatalytic hydrogen generation rate of 41.26 mmol g⁻¹ h⁻¹ under visible light. The Ni–S bonds on the close contact interface between CZS and Ni₂P can be act as electron-bridge to provide a channel for electron transfer. During the photocatalysis processing, Ni₂P can be used as electron traps to attract electrons from CZS, resulting in the improvement of the photocatalytic performance.