Studies on electrochemical photovoltaic cells formed with as-deposited in-doped CdS films

Indium doped and undoped CdS films have been deposited on conducting substrates by a chemical bath deposition technique. The doping concentration was varied from 0.005 to 1.0 wt. % of indium. Electrochemical photovoltaic (ECPV) cells are formed with these films and their electrical properties are studied. It is observed that the performance of the cell measured in terms of open circuit voltage (Voc), short circuit current (Isc), efficiency (η), and maximum power output (Pm), is optimum for the cells formed with 0.01 wt. % In-doped CdS photoanode.     

Thickness dependent properties of electro-chemical-photovoltaic (ecpv) cells formed with chemically deposited CdS films

Thin polycrystalline cadmium sulphide photoelectrodes of various thicknesses have been deposited on polished stainless steel substrates by a chemical bath deposition technique. The electrochemical photovoltaic (ecpv) cells were formed with these photoanodes. Short circuit current (Isc) and open circuit voltage (Voc) are recorded under 100 mW/cm² light intensity. It is found thatIsc increases with increase in thickness of the photoanode whereasVoc remains more or less constant. The other cell parameters, maximum power output (Pm) and efficiency (η) are found to improve with increasing thickness, while fill factor (f.f.) varies slightly with the photoanode thickness. The semiconductor-liquid space charge region capacitances in the dark were measured. The variation of 1/C ² versus applied reverse biasV is nonlinear. The deviation from straight line behaviour is attributed to the existence of surface states and degeneracy of states. The flat band potential is determined from the extrapolation of the (1/C ²) −V plot to the voltage axis, and is found to vary with the thickness of the photoanode.     

Effects of copper doping on the electronic properties of CdS films sintered with CdCl2

Chlorine- and copper-doped polycrystalline CdS films were prepared by coating a slurry which consisted of CdS, CdCl₂, CuCl₂ and propylene glycol on a glass substrate and sintering in a nitrogen atmosphere, to investigate the effects of copper doping on the window properties of all-polycrystalline CdS/CdTe heterojunction solar cells. The variations of carrier concentration as a function of the amount of copper doping in CdS films which were doped with the order of 10¹⁸ cm^–3 chlorine have been explained in terms of electronic compensation of the copper impurity. The variations of optical transmission spectra as a function of copper doping have been correlated with the variations of photoconductivity spectra. Even 10 p.p.m. copper in the sintered CdS films degrades the window properties of the CdS films significantly. The degradation is caused by reduced optical transmission rather than by an increase in electrical resistivity.     

Reflection properties of oriented thin CdS films formed by laser ablation

Oriented thin (≈2 μm) films, CdS, prepared by laser ablation were characterized by the dependence of external and internal reflection on both the angle of incidence and the polarization of laser light. The samples exhibit perpendicular and parallel orientation of the crystallographic axis with respect to the surface of the glass substrate. The experiments were performed at 300 K using low intensity (<1 W/cm²) cw emissions at 476.5, 514.5 and 632.8 nm of argon and He–Ne lasers respectively. For blue and green light, the results are very well described by the theoretical models based on Fresnel reflection. In contrast to the external features, the internal reflectance exhibits dichroism and birefringence of the samples at 514.5 nm, revealing the sensitivity of the internal reflection technique to the optical anisotropy of the films. Considering multiple-beam interference, the model of Fresnel also describes satisfactorily the results for red light. However, a rather sensitive dependence on the incoming He–Ne laser intensity was observed. In fact, by increasing the intensity of 64 mW/cm² by about one order of magnitude, only the external reflectance shows good agreement with the theory, whereas the internal reflection properties are obviously influenced by additional effects, such as non-linear change of the optical constants, which are not included in Fresnel reflection considerations.     

Control of aluminum doping of ZnO:Al thin films obtained by high-power impulse magnetron sputtering

This work reports a method used to control Al doping of ZnO thin films deposited by high-power impulse magnetron sputtering of a pure Zn target in low-pressure Ar/O₂ gas mixture. The method uses sputtering of an electrically negative biased aluminum electrode placed in the proximity of the negative glow of the magnetron discharge. Resonant laser absorption measurements of Al atom concentration in vapor phase and the X-ray Photoelectron Emission Spectroscopy measurements of Al concentration in the deposited ZnO:Al films confirm that the electrode biasing potential is the key parameter that controls the Al doping process. Optically transparent ZnO:Al films with resistivity as low as 3.6 × 10^− 3 Ω × cm have been obtained at an optimum value of Al concentration of 1.5 at.%. It has been found that the film electrical conductivity is limited by the effect of decreasing of crystalline grain size in the films with the increased Al doping concentration.     

Annealing effects on the chemical deposited CdS films and the electrical properties of CdS/CdTe solar cells

CdS layers grown by chemical bath deposition (CBD) are annealed in the oxygen and argon-hydrogen atmosphere respectively. It has been found that the open circuit voltage of the CdS/CdTe solar cell increases when the CBD CdS is annealed with oxygen before the deposition of CdTe by close spaced sublimation (CSS), while the performance of the solar cell decreases when the CBD CdS is annealed with argon-hydrogen. Electronic properties of the CdS films are investigated using X-ray photo-electron spectroscopy (XPS), which indicates that the Fermi level is shifting closer to the conduction band after annealing in the oxygen and consequently a higher open circuit voltage of the solar cell can be obtained.     

Effect of Al doping on structural and dielectric properties of PLZT ceramics

Polycrystalline samples of Al modified lead lanthanum zirconate titanate [PLZT] with Zr = 55% and Ti = 45%, have been synthesized by a high-temperature solid-state reaction technique. X-ray diffraction analysis of the compounds suggests the formation of a single-phase compound with tetragonal structure. Dielectric studies of the compounds as a function of temperature (from 30 to 350°C) at frequency (1, 10 and 100 kHz) show that the compounds undergo a phase transition of diffuse type.The transition temperature shifts towards higher side with increase in frequency a typical characteristic of a relaxor material. Diffusivity (γ) study of phase transition of these compounds provided its value between 1 and 2, indicating the variation of degree of disordering in the system. Measurement of dc resistivity (ρ) as a function of temperature (Room temperature, RT to 350°C) at a constant biasing field suggests the compounds have negative temperature coefficient of resistance (NTCR).     

Effect of thermal treatment on some properties of electrodeposited CdS thin films

An analysis of the influence of the temperature of thermal treatment on the properties of electrodeposited thin films of CdS has been carried out. The transition from cubic to hexagonal phase, and the changes of grain size and resistivity are studied.     

Effects of aluminum doping on lanthanum oxide gate dielectric films

This work reports a novel method for improving the electrical properties of lanthanum gate oxide (La₂O₃) by using aluminum doping and rapid thermal annealing (RTA) techniques. In the bulk of the Al-doped La₂O₃ film together with 600 °C RTA, we found that the aluminum atoms were incorporated into the oxide network and the film was transformed into lanthanum aluminate complex oxide. At the interface, a thin Al₂O₃ layer was formed. This interfacial Al₂O₃ layer suppressed the out-diffusion of substrate Si, the formation of interfacial silicate layer and silicide bonds. These effects resulted in a significant reduction on the bulk and interface trap densities and hence the gate leakage current.     

Effect of doping on properties of Zno:Cu and Zno:Ag thin films

ZnO:Cu and ZnS thin films were grown by metal-organic chemical vapour deposition (MOCVD) under atmospheric pressure onto glass substrates. The ZnO:Ag films were fabricated from ZnS films by non-vacuum method that consists of simultaneous oxidation and Ag-doping by the close spaced evaporation (CSE) of silver at the temperature of 500–600 °C. Photo-assisted rapid thermal annealing (PARTA) at ambient air during 10–30 s at the temperature of 700–800 °C was used for the ZnO:Cu films. The samples were studied by X-ray diffraction technique (XRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The grain size of ZnO:Cu films increased with an increase of Cu concentration. PL spectra of as-deposited ZnO:Cu films depended on Cu concentration and contained the bands typical for the copper. After PARTA at high temperature the emission maximum shifted towards the short-wave region. During the fabrication of ZnO:Ag films the grain growth process was strongly affected by the Ag loading level. The grain size increased with an increase of Ag concentration and ZnO:Ag films with surface roughness of 8 nm were obtained. Observed 385 nm PL peak for these samples can be attributed to the exciton–exciton emission that proves the high quality of the obtained ZnO:Ag films.     

Effect of the europium doping on the structural and luminescent properties of yttrium aluminum garnet

Europium activated yttrium aluminate (YAG:Eu) phosphors were synthesized using urea by wet chemical synthesis route. The luminescent behavior and the microstructural changes are monitored, depending on the amount of europium. The luminescent spectra of YAG:Eu phosphors possess four major emission bands in the range of 570–700 nm with maxima situated at 592 nm 598 nm, 611 nm and 631 nm. The intensity ratio between the 611 nm band as red component (⁵D₀ → ⁷F₂) and 592 nm band as orange component (⁵D₀ → ⁷F₁) is discussed, in order to obtain information about the chemical surroundings of the luminescent centers and their symmetry. X-ray diffraction showed that the main crystalline phase of the phosphors is yttrium aluminum garnet Y₃Al₅O₁₂ with cubic structure. Monoclinic Y₄Al₂O₉ phase was also found as impurity. The effect of the europium content on the microstructural parameters is revealed. The luminescent characteristics depend strongly on the structural purity, activator concentration and incorporation of europium ions in the host lattice. Additional investigations as FT-IR, BET, ICP-OES were performed for a better understanding of the luminescent and structural characteristics of YAG:Eu phosphor.     

CdS多晶薄膜的制备及性质研究

分别采用近空间升华法和电子束蒸发法在透明导电玻璃和普通载玻片上制备了硫化镉(CdS)多晶薄膜.对制备样品的表征结果表明:(1)两种方法制备样品都沿(002)晶向择优生长,属于六方相多晶结构,但择优取向度不同;(2)CdS薄膜表面连续而致密,粒径均匀,但两种工艺制备样品的S:Cd原子比有较大差异;(3)CdS薄膜的光能隙在2.39～2.44eV之间,电子束蒸发制备样品光能隙稍小.分析认为,两种方法制备样品的上述差异可能与衬底温度、沉积时间及成膜机制的不同相关.     

Photoelectronic properties of (Cu, Fe, Al) incorporated CdS thin films

CdS films, undoped and doped with Al, Cu, and Fe were prepared by the spray pyrolysis technique. The films have a polycrystalline hexagonal structure as shown from their XRD patterns. The crystallinity of pure CdS film is highly distorted by the addition of Al, or Fe, or Cu. The a.c. photoconductivity for the prepared samples was measured. The photoconductivity response spectra show two distinct peaks independent of the incorporated element. The position and intensity of these peaks are affected by the type and concentration of the elements incorporated. The optical absorption coefficient for the samples investigated, as calculated from transmission and reflection spectra, was studied as a function of photon energy. The pure CdS sample shows a sharp absorption edge while the incorporated films show a less sharp curve. The incorporation of Al enhances the d.c. photosensitivity response.     

Effect of Bi3+ doping on the properties of chemically deposited GdS films

CdS films were prepared by a chemical bath deposition technique with different Bi concentrations (0.01 to 5 wt %) on glass substrates. Optical and electrical properties were studied with these films. It was observed that the absorption coefficient of the CdS film increases with Bi-doping up to 2 wt % and then decreases. These results are explained in terms of the crystallanity of the film. The optical band gaps (E_g) were determined and found to decrease with Bi-doping. The conductivity and thermoelectric power are higher for doped films than undoped CdS films. These results are explained by considering the existance of Cd²⁺ ions as donor centres in Bi-doped CdS films.     

Electrical properties of vacuum annealed CdS films

Cadmium sulphide (CdS) films were evaporated in vacuum on glass substrates maintained at room temperature. These films were later annealed in vacuum at temperatures in the range 30 to 300° C. The variation of d.c. electrical conductivity was studied in the temperature range 100 to 300 K. While the conductivity data in the range 100 to 150 K were observed to follow Mott's variable range hopping process, the conductivity in the high-temperature region (150 to 300 K) could be explained by Seto's model.     

The properties of bismuth-doped vacuum-evaporated CdS films

The effect of doping with bismuth on various properties of vacuum-evaporated CdS films was studied. The properties specifically studied were (1) the dark conductivity and photoconductivity as functions of the temperature and doping concentration, (2) the Hall mobility and carrier concentration at room temperature, (3) the thermally stimulated current and (4) the optical absorption and spectral response. It was found that on doping with bismuth the dark conductivity decreases and the photosensitivity increases significantly. These phenomena probably arise from the formation of cadmium vacancies due to bismuth doping. Studies of the Hall effect show that the carrier concentration is reduced by doping with bismuth. Investigations of thermally stimulated currents for both pure and doped films show that the trap concentrations are reduced by doping.     

Effect of platinum doping on the structural and electrical properties of SnO2 thin films

The investigation of Pt doping effect on the structural and electrical properties of SnO₂ thin films was aimed in this study. For this purpose, the polycrystalline pure and Pt-doped SnO₂ thin films were deposited onto n-type silicon substrate and the Pt sputter power was varied as 0 (un-doped), 2, 5 and 7 W by using radio frequency confocal sputtering system. The structural properties of the samples were analysed by X-ray diffraction measurements. The structural results show that the 5 W Pt-doped SnO₂ sample has better crystallinity than the other samples. The results of the electrical measurements as current–voltage, capacitance–voltage and conductance–voltage were also obtained and discussed in detail for fabricated diodes. The analysis of electrical characteristics shows that the use of different Pt doping has significant effect on electrical properties of such devices. The study also provides an improved supplemental understanding to the related technologies which use Pt-doped SnO₂ materials.