Transparent CdS Research Articles

Structural, morphological, optical analyses of Ni-doped CdS thin films and their photovoltaic performance in hybrid solar cells

This work reports influences of variation in Ni-doping on structural, morphological, and optical properties of CdS thin films and in their hybrid solar cell applications. X-ray diffraction data showed that increase of Ni-doping in CdS structure caused not only a broadening in CdS peak but also a decrease in the intensity of main cubic CdS peak. Morphological studies illustrated that lower amount of Ni-doping treatment firstly reduced the grain size of CdS thin films, whereas higher concentration of Ni-doping led to bigger grains. The best transparent CdS sample was achieved for 1 at% Ni-doping as 95% at 675 nm. Compared with CdS thin films (2.98 eV), bandwidths of Ni-doped CdS samples gradually increased and reached to 3.39 eV, which is due to the existence of strong quantum confinement effect. Photoluminescence (PL) data of the device demonstrated that the most efficient electron transfer was accomplished at CdS/P3HT interface for 1 at% Ni-doping because this device demonstrated the lowest PL peak intensity. Current density–voltage (J–V) characteristics of CdS-based device exhibited a power conversion efficiency (PCE) of 0.296% and it enhanced to 0.663% for device including 1 at% Ni atoms, which is most probably due to achievement of most efficient exciton dissociation between CdS and P3HT layers as approved by PL results. However, with increasing Ni-doping amount up to 3 at% and 5 at%, PCE values were in turn obtained as 0.131% and 0.208%, indicating a deterioration in PCE value of cells, which might be due to the less efficient exciton dissociation at the interface. Further increase of Ni-doping to 7 at% led to an efficiency value of 0.417%, which is still lower than that of 1 at% Ni-doped CdS-based device.

A novel synthesis and characterization of transparent CdS thin films for CdTe/CdS solar cells

We demonstrate the direct synthesis of CdS thin films by spin coating method with thiol-amine co-solvents system. Annealing of the films at various temperatures has been performed in the air using simple glass protector. The XRD patterns show a strong peak along (110) plane related to cubic lattice while two weak peaks at (002) and (100) planes indicate the hexagonal symmetry for the CdS thin films. The Raman peak at 305 cm−1 also confirms the formation of crystalline CdS thin films. The FTIR study also reveals the formation of CdS thin films. The SEM images reveal the surface uniformity and homogeneity of the CdS thin films. The EDX results indicate nearly stoichiometric CdS thin films. The optical band gap of CdS thin films is ~ 2.4 eV when coated at 2000 rpm and annealed at 300 °C for 5 min. These findings indicate that synthesized CdS films are potential candidates for solution-processed CdTe/CdS solar cells.

A research on growth and characterization of CdS:Eu thin films

Chemical spray pyrolysis-grown CdS thin films including various quantities of Eu atoms (from 0 to 10 at.%) were synthesized on glass slides. The detailed physical properties of the produced CdS and CdS:Eu thin films were explored. Structural analysis showed that Eu-doping enhanced the crystal quality of CdS thin films until 10 at.% Eu-doping and further Eu-doping treatment led to a distortion in the CdS structure. In addition, the crystallite sizes of CdS thin films dropped from 36.2 to 32.4 nm as Eu-doping level increased to 10 at.%. Morphological data showed that increasing Eu-doping remarkably varied the surface morphology of CdS thin films forming smaller grains. Chemical content examinations approved the presence of Eu atoms in CdS structure. From the optical measurements, it was obtained that more transparent CdS thin films with a maximum transmittance of 68% at 820 nm were created after 10 at.% Eu-doping and bandgap values of samples reduced from 2.58 to 2.47 eV with rising of Eu-doping from 0 to 10 at.%. Room temperature photoluminescence data demonstrated the formation of two essential peaks for all the samples, which are in turn related to green and yellow bands. Electrical investigation pointed out that Eu-doping enhanced the carrier density of CdS thin films from 4.38 × 1013 cm− 3 to 2.46 × 1014 cm− 3 and dropped the resistivity of CdS samples from 2.59 × 104 Ω cm to 5.85 × 103 Ω cm until 6 at.% and further increment of Eu-doping paved the way to get worse electrical data. Thus, it can be brought a conclusion that Eu-doping not only improved the optical properties of CdS thin films, but also restored the electrical properties, which are able to use in the opto-electronic devices.

Realizing near stoichiometric and highly transparent CdS:Mo thin films by a low‐cost improved SILAR technique

Undoped and molybdenum doped CdS thin films were deposited on glass substrates using Improved Successive Ionic Layer Adsorption and Reaction (ISILAR) technique. The Mo doping level was varied from 0 to 15 at.% in steps of 5 at.%. The XRD analysis shows that all the films are polycrystalline with cubic structure and grow preferentially along the (111) plane. The crystallite size increases gradually with the increase in Mo doping level up to 10 at.% and decreases with further doping. The morphological studies reveal that Mo doping significantly affects the grains size. Qualitative and quantitative compositional analysis show that near stoichiometric undoped and Mo doped CdS thin films can be achieved using this ISILAR technique. All the films exhibit high transparency in the visible region with an average transmittance in the range of 85–95%.

High-efficiency, flexible CdTe solar cells on ultra-thin glass substrates

Flexible, high-efficiency, low-cost solar cells can enable applications that take advantage of high specific power, flexible form factors, lower installation and transportation costs. Here, we report a certified record efficiency of 16.4% for a flexible CdTe solar cell that is a marked improvement over the previous standard (14.05%). The improvement was achieved by replacing chemical-bath-deposited CdS with sputtered CdS:O and also replacing the high-temperature sputtered ZnTe:Cu back contact layer with co-evaporated and rapidly annealed ZnTe:Cu. We use quantum efficiency and capacitance-voltage measurements combined with device simulations to identify the reasons for the increase in efficiency. Both device simulations and experimental results show that higher carrier density can quantitatively account for the increased open circuit voltage (VOC) and Fill Factor (FF), and likewise, the increase in short circuit current density (JSC) can be attributed to the more transparent CdS:O.

In-situ growth of a CdS window layer by vacuum thermal evaporation for CIGS thin film solar cell applications

Highly crystalline and transparent CdS films are grown by utilizing the vacuum thermal evaporation (VTE) method. The structural, surface morphological, and optical properties of the films are studied and compared with those prepared by chemical bath deposition (CBD). It is found that the films deposited at a high substrate temperature (200 °C) have a preferential orientation along (002) which is consistent with CBD-grown films. Absorption spectra reveal that the films are highly transparent and the optical band gap values are found to be in a range of 2.44 eV–2.56 eV. CuIn1−xGaxSe2 (CIGS) solar cells with in-situ VTE-grown CdS films exhibit higher values of Voc together with smaller values of Jsc than those from CBD. Eventually the conversion efficiency and fill factor become slightly better than those from the CBD method. Our work suggests that the in-situ thermal evaporation method can be a competitive alternative to the CBD method, particularly in the physical- and vacuum-based CIGS technology.

A steady blue-emitting CdS nanocrystals-polystyrene composites

CdS nanocrystals with narrow size distribution were synthesized in an organic solution and transparent CdS nanocrystals/polystyrene composite films were fabricated. Transmission electron microscopy, energy dispersive X-ray spectroscopy, photoluminescence and Raman spectra were adopted to investigate these samples. The result of photoluminescence measurement shows that the composite films exhibit distinct luminescence properties of more stable emission and a narrower full-width at half-maximum than that of CdS nanocrystals in solution. Detailed analysis of the Raman spectra has enabled us to identify the origin of the optimized optoelectronic properties of the CdS nanocrystals-polystyrene composites films.

The influence of the substrate temperature on the photovoltaic properties of spray-deposited CdS:In thin films

Polycrystalline and highly transparent CdS:In thin films were produced by the spray pyrolysis (SP) technique at different substrate temperatures ranging from 350 to 490 °C on glass substrates. The effect of the substrate temperature on the photovoltaic properties of the films was investigated by studying the transmittance measurements, X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) observations and the I– V plots. The transmittance measurements were used to estimate the band gap energy by the linear fit of ( αhν) 2 versus hν. The band gap energy was found to be slightly increasing with the substrate temperature. XRD diffractograms show that a phase transition from the cubic to the hexagonal phase occurs by increasing the substrate temperature, beside more orientation of crystal growth. Also they show that complex cadmium compounds are still present till T s ≈ 460 °C after which they practically disappear. From the linear I– V plots the resistivity was estimated and found to be strongly decreasing with the substrate temperature.

Cadmium sulfide thin films prepared by chemical bath deposition method

The properties of chemical bath deposited CdS thin films were investigated. It was found that the thickness and crystallinity of the films were affected by the pH value and temperature of the solutions. Transparent CdS films with thickness of around 40 nm were obtained within 5 min. deposition when the conditions of the solution were controlled to pH 8–10 and 80–90°C. Some CdS/semiconductor (Si or CIS) junctions were made, tentatively. A linear relation between 1/ C 2 and V was observed for these junctions.

Effects of Cadmium Particle Size on Properties of Sintered CdS/CdTe Thin Film Solar Cells

Transparent CdS films with low electrical resistivity have been prepared by coating a CdS slurry on a glass substrate followed by sintering in nitrogen. CdTe slurries consisting of Te powder, Cd powders of various particle sizes, and an appropriate amount of propylene glycol were coated on the sintered CdS films and were sintered in nitrogen to prepare sintered CdS/ CdTe solar cells. The efficiency of a sintered CdS/ CdTe solar cell increases with increasing Cd particle size up to 3–4 μm and then decreases with a further increase in the Cd particle size. The microstructures of the sintered CdTe layer and of the cross-section of the CdS/CdTe solar cell show that the structures are the most compact in a solar cell which started with a Cd particle size of 3–4 μm. A sintered CdS/CdTe solar cell that was fabricated by using a Cd powder with an average particle size of ∼ 4 μm shows a solar efficiency of 12% when measured under a solar intensity of 80 mW cm−2. PM/0575

Synthesis of porous quantum-size cadmium sulfide membranes: photoluminescence phase shift and demodulation measurements

Optically transparent CdS membranes have been synthesized. Colloidal Q-CdS particles (particle diameter d{sub p} < 40 {angstrom}) carrying short phosphate chains and excess Cd{sup 2+} ions have been directly converted into a microporous membrane form. By controlling ionic strength and particle concentrations, one can link self-organized fusion-free aggregates and avoid formation of powder-like flocculation products. The resultant unsupported membranes exhibit different mechanical properties (e.g., rigidity, delayed elasticity, and solubility) in the presence of water depending upon the preparation method employed. The membrane form of CdS has distinctively different photophysical properties than the precursor colloidal form. Conversion of weakly red luminescent colloids (broad band at 700 nm) into membranes activated an intense room temperature band edge luminescence (BEL) (narrow bands between 450 and 500 nm) attributed to the recombination of excitons and/or shallowly trapped electron/hole pairs.

Photovoltaic properties of CdS/CdTe solar cells sintered with CdCl 2

Transparent CdS films on glass substrates were prepared by coating with a CdS slurry which contained 10 wt% CdCl 2 followed by sintering in nitrogen. All-polycrystalline CdS/CdTe solar cells have been fabricated by coating the CdS layer with a CdTe slurry, which contained various amounts of CdCl 2, and sintering at 625° C for 1 h in nitrogen. The amount of CdCl 2 was varied from 1 wt% to 10 wt%. The presence of CdCl 2 is the CdTe layer before sintering improves the micostructures of the sintered CdTe layer and the junction. Both of these effects lead to improved solar cell efficiency. When the amount of CdCl 2 is large, it causes a dreduction in the hole concentration of the CdTe layer. This is presumably caused by chlorine doping and the formation of a thick layer of CdS 1−x Te x at the compositional interface which degrades the efficiency of the solar cell. A solar efficiency of 12.5% under 85 mW/cm 2 of solar illumination was observed in a CdS/CdTe solar cell that was fabricated by coating a sintered CdS film with a CdTe slurry, which contained 4.5 wt% CdCl 2, and by sintering the CdS-CdTe composite at 625°C in nitrogen.

On the dispersion of the refractive index in AIIBVI thin films

AbstractWe propose a new calculation following traditional methods for deducing refractive index from the fringe pattern of the transmission spectrum of a thin transparent CdS, ZnS, and ZnxCd1−xS film surrounded by nonabsorbing media. The error in the refractive index measurements is 4–5%. We have found that polycrystalline CdS, ZnS, and ZnxCd1−xS evaporated films have refractive index different from those of single crystal material.