Window Layer In Solar Cells Research Articles

Annealing temperature assisted microstructural and optoelectrical properties of CdSe thin film grown by RF magnetron sputtering

Abstract Cadmium selenide (CdSe) thin films are widely used in electronic devices as well as a potential window material in solar cell applications. In this study, 100 nm CdSe thin films were grown on borosilicate glass substrates by using Radio Frequency (RF) magnetron sputtering technique at room temperature (25 °C). Deposited films were annealed in a vacuum furnace at 100 °C, 200 °C, 300 °C, 400 °C and 500 °C for 10 min, respectively. In-depth analysis of the microstructural and optoelectrical properties of annealed films were performed using X-ray diffraction (XRD), UV–Vis spectrometry and Hall Effect measurements. From XRD results, the films illustrated hexagonal structure with preferred orientation (002) at 2θ = 24.12°. UV–Vis study indicated that the transmission ranges were from 75% to over 85% for annealed samples and the calculated optical band gap was in the range 1.65 eV–1.73 eV. Optical properties demonstrated that CdSe had the potential to be incorporated as a window layer in solar cells. Meanwhile, the electrical measurements showed n-type conductivity with the carrier concentration of 1014 cm−3 for all the annealed films. The optimized results recommend sputtered CdSe thin films annealed at 400 °C as a possible window layer to the Cd-based solar cells.

Experimental and theoretical studies of the solid-state performance of electrodeposited Yb2O3/As2Se3 nanocomposite films

The influence of the rare-earth oxide (Yb2O3) on arsenic selenide (As–Se) host is currently investigated and documented in this study. Nanocomposite films were grown using the electrodeposition (ED) technique with the addition of 1 – 4 mol% Yb2O3. The film’s optical structural, optical, morphological, and electronic features were studied. The host matrix presents the monoclinic structure whereas the composite films present two phases –cubic and orthorhombic crystal structure. Crystallites within nano sizes (36.2 nm) were recorded for the pristine film while the composite films showed sizes ranging from 37.2 to 48.1 nm. Moreover, the Raman spectra revealed low energy Raman phonons characteristic of Se8 rings, As4Se4 cages, As–Se hetero-polar bonds whose cleavage was due to the diffusion of the Yb ions into the host matrix as shown by the Raman shift. More so, the refractive index peaked at n = 2.66 in the λ interval of 350–600 nm, while the SEM images showed nano-balls and nanoclusters which are fairly homogeneous. PL studies exhibited multimode emission bands spanning the UV–Vis–NIR regions. First-principles calculations were employed to investigate the structural properties and electronic structure of the pristine (As–Se) film, as well as Yb contribution. It was found that Yb addition leads to reduce the bandgap energy and consequently the lone pair p-states of Se contribute nearby to Fermi energy level. Hence, the experimental and theoretical results of films afford potential applications in phase-change memory (PCM) and downconverting solar cell window layer.

Structural, optical and optoelectrical analysis of a new window layer based on ZnAl2S4 thin films

In this work, we report the manufacturing of neoteric window layers based on ternary chalcogenide ZnAl2S4 films utilizing an inexpensive spray pyrolysis method for the first time. Three films (228 nm, 262 nm, and 319 nm) have been prepared. The X-ray diffraction was applied to check the cubic phase of the ZnAl2S4 films. The morphology analysis depicted that the 262 nm film has the lowest porosity and roughness as compared with other films. This affects its refractive index values which correspondingly sheds an impact on its optical/optoelectrical parameters. ZnAl2S4 films revealed the n-type conductivity and this has been confirmed via the hot-probe experiment. Furthermore, our results displayed that the ZnAl2S4 thin films exhibited a wide energy gap in the extent of 3.68–4.01 eV along with good optical conductivity. Hence, the ZnAl2S4 films could be a suitable new economic window layer in solar cells. Besides, the 319 nm film has presented a prominent enlargement in the nonlinear optical parameters as compared to other inspected films which could be a good sign of utilizing this material in nonlinear optical devices.

Band structure controlled solid solution of spray deposited Cd1-x ZnxS films: Investigation on photoluminescence and photo response properties

Nano crystalline Cd1-xZnxS (x = 0.00–1.00 at. %) films were deposited on glass substrates through conventional chemical spray pyrolysis method at different temperatures. The films with x < 0.70 have exhibited hexagonal phase beyond which cubic phase was noticed. The shifting of XRD peaks with higher Zn content, confirmed the formation of Cd1-xZnxS solid solutions. The film crystallinity improved at higher deposition temperatures, while it decreased with increasing x. SEM images showed nearly spherical granular shapes for x = 0, which gradually deteriorate in size at higher x and changed to fibrous structure for x > 0.60. Further the films with x = 0.40–0.60 seem to be porous and well-suited for gas sensing applications. The EDS confirmed the presence of Cd, Zn and S with expected stoichiometry. The optical transmittance and the energy band gap increased with increasing temperature and x. The shift of absorption edge to the shorter wavelength with Zn content has made film high transparent in blue region. The extinction coefficient reduced with x and Urbach energy has shown the formation of defects. Photoluminescence spectra exhibited broad emission bands which could be deconvoluted to multiple peaks attributable to defect states. The film resistivity increased with x that resulted in decrease of carrier concentration which was determined through Hall Effect measurements. The crystallinity was found to influence the photo-response of the films. The films with high Cd contents showed excellent photo response which can be used as photo-detector due to its rapid decline of resistance in the band edge region. The smaller grain and fibrous structured films with large open surface area obtained here, can be used in gas sensing while, the films with x > 0.60 are well-suited for the fabrication of window layers of solar cells.

Exploring the direct effect of intermediate band semiconductor materials on the structural, thermal and optical properties of PMMA nanocomposite

In this work, polymethylmethacrylate (PMMA) doped with SnS2, Sn0.75Fe0.25S2, and Sn0.75Cr0.25S2 nanoparticles films were prepared using both thermolysis and casting procedures. The purity, structural and shape of the nanofillers were confirmed by Rietveld refinement method. The compositional changes for nanocomposite films were studied by energy dispersive spectrometry technique. Nanoparticles morphology and particle size were examined by transmission electron microscopy (TEM) technique. Proper interactions between added nanofillers and the polymer matrix were discussed in detail by Fourier transform infrared spectroscopy technique (FTIR). The variations in the FTIR absorption bands position and their shape proved the effect of doping on the composite films. The effect of dopant elements on the thermal properties of PMMA polymer matrix has been investigated by thermogravimetric analysis (TGA). Results showed an improvement in the degradation temperature of doped polymers compared to undoped ones. Clear regular arrangements of images for nanoparticles and composite films have been represented by scanning electron microscopy (SEM). Different optical parameters have been examined using UV–vis spectroscopy technique. Due to the high transmittance values in the wavelength range of 320–800 nm, the formed composite films could be used as protective window layers for solar cells. The energy gap values decreased from 4.3 eV for undoped PMMA polymer to 4, 3.85, and 3.16 eV depending on the doping element.

Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method

The CdS nanostructure thin films have been deposited on glass substrates the usage of dip coating method. The structural, optical and surface morphologies of CdS nanostructure thin film were investigated by XRD, SEM, TEM, EDAX, UV–Vis and PL spectra. The outcomes indicated the films were hexagonal shape and the grains are spherically formed and allotted uniformly over the complete surface of the glass substrate. The impact of quantum confinement and the shifts in optical band gap had been calculated. The results indicated CdS nanostructure thin film is appropriate for solar cell window layer application and the solar cell conversion efficiency was calculated.

Effect of synthesis parameters on the structural, optical, morphological and electrical properties of n-type CTS nanostructures

In this work we have prepared n-type copper tin sulphide (CTS) quantum dot thin films for efficient window layers of solar cells. The change in type of CTS was achieved by the use of Triethanolamine (TEA) as the complexing agent. Studies were made on CTS thin films by changing the amount of complexing agent and also by changing the Cu:Sn and S:Sn ratios. All the samples showed low absorbance and high transmittance in the visible and infra red regions. The bandgaps are high enough to be used in buffer layers. Increasing the amount of TEA increased the crystallite size and thereby decreased the bandgap. Presence of excess copper in the material enhanced the conductivity of the material largely and also lead to the formation of Schottky barriers making Cu rich samples useful in rectification too. Increased sulphur content has been found to improve the crystallinity of CTS thin films.

Investigation on nebulizer spray coated Nd-doped SnS2 thin films for solar cell window layer application

Economic nebulizer spray pyrolysis (NSP) technique has been employed to deposit Neodymium (Nd) doped Tin disulfide (SnS2) thin films at 325 °C by varying the doping concentration of Nd (0%, 2%, 4% and 6%). The impact of Nd concentration on crystalline structure, morphology and opto-electronic properties of films were studied using X-ray diffraction (XRD), FT-Raman spectrophotometer, atomic force microscope (AFM), energy-dispersive X-ray spectroscope, scanning electron microscope (SEM), UV–Visible spectrometer and Hall Effect measurements. Structural parameters such as lattice constants, texture orientation factor, micro strain, dislocation density and crystallite size were estimated using XRD data. The SEM and AFM images of films displayed an exceptional morphology. The surface roughness of the films was found to increase with the increase of dopant concentration. Optical analysis done on the films revealed variation in band gap from 2.75 to 2.92 eV as the Nd doping concentration is increased from 2 to 6%. SnS2 thin film exhibited n-type conductivity as, confirmed from Hall Effect studies. The resistivity and concentration of the carrier in the film were found to be 4.17 × 10−2 Ω cm and 4.06 × 1017 cm−3 respectively which were then correlated to the deposition parameters. Furthermore, FTO/n-Nd-SnS2/p-SnS hetero-junction based solar cells were prepared and their current voltage curve in dark condition was obtained.

Gadolinium doping effect on SnO2 thin films optical and electrical properties

Undoped SnO2 thin films, as well as Gd-doped SnO2 thin films, were deposited on glass substrate by spray pyrolysis technique. The effect of gadolinium concentration and substrate annealing on structural, optical and electrical properties of SnO2 films are investigated. The structural properties of these thin films were analyzed using x-ray diffraction (XRD). XRD analysis confirmed the polycrystalline tetragonal crystalline structure of the films with mainly (110) preferential growth plane. The crystallite size has been reduced from 35 nm to 15 nm with increasing Gd dopant concentration. The films optical transmittance spectra exhibit high transparency of about 76%–87% in visible region. The films optical gap is enlarged from 3.43 eV in the un-doped films to 3.71 eV when Gd doped. The films figure of merit revealed a maximum value of about 8.2 × 10–3(Ω/sq)−1 at 550 nm wavelengths. The highest conducting and transparency are obtained in the film prepared with 3 wt% Gd doping ratio. Hence, we conclude that 3 wt% ratio is the optimal one required for Gd:SnO2 film production that may found optoelectronic applications, in particular, as window layer in solar cells.

Thickness and gamma-ray effect on physical properties of CdO thin films grown by pulsed laser deposition

Polycrystalline Cadmium Oxide (CdO) thin films were preparedusing pulsed laser deposition onto glass substrates at roomtemperature with different thicknesses of (300, 350 and 400)nm,these films were irradiated with cesium-137(Cs-137) radiation. Thethickness and irradiation effects on structural and optical propertieswere studied. It is observed by XRD results that films arepolycrystalline before and after irradiation, with cubic structure andshow preferential growth along (111) and (200) directions. Thecrystallite sizes increases with increasing of thickness, and decreaseswith gamma radiation, which are found to be within the range(23.84-4.52) nm and (41.44-4.974)nm before and after irradiation forthickness 350nm and 400nm respectively, The dislocation density,microstrain and number of crystallites per unit surface area,decreases with increasing of thickness, while they increases withgamma radiation. From the atomic force microscope (AFM), thegrain size of CdO films decrease from 96.69nm before radiation to89.49 nm after gamma radiation and RMS roughness increases forthe irradiated sample from 4.26nm to 4.8nm, increase in the surfaceroughness is advantages as it increases the efficiency of the CdOsolar cells. The optical properties for thin CdOfilms with differentthickness before and after gamma irradiation have been determinedand reveals direct energy gap. It is decrease with the increase ofthickness, while it is increase after gamma irradiation. These films apromising candidate for the window layer in solar cells and otherpossible optoelectronic application.

Optical properties of ZnO/MgF2 bilayer thin films prepared by PVD technique

Zinc Oxide (ZnO) is considered as one of the best materials already used as a window layer in solar cells due to its antireflective capability. The ZnO/MgF2 bilayer thin film is more efficient as antireflective coating. In this work, ZnO and ZnO/MgF2 thin films were deposited on glass substrate using pulsed laser deposition and thermal evaporation deposition methods. The optical measurements indicated that ZnO thin layer has an energy gap of (3.02 eV) while ZnO/MgF2 bilayer gives rise to an increase in the energy gap. ZnO/MgF2 bilayer shows a high energy gap (3.77 eV) with low reflectance (1.1-10 %) and refractive index (1.9) leading to high transmittance, this bilayer could be a good candidate optical material to improve the performance of solar cell window.

The Effects of Sputtering Time on Cds Thin Film Solar Cell Deposited by DC Plasma Sputtering Method

CdS thin films of different thickness have been prepared by dc sputtering technique on glass slides for a window layer of solar cells. The CdS target were sputtered in different sputtering times (1,1.5,2.5,3) hrs, working pressure (2×10-2) mbar and discharge voltage(2) kV.The structure of the nanoparticles films was investigated of CdS thin films by X-ray diffraction (XRD).The XRD patterns showed that the films were hexagonal (wurtzite) structure having strong preferential orientation along the (002) plane with particle size in the range of (41.04-41.46-41.88-42.53) nm, the peak at (002) preferred orientations of the films are shifted a little from left to right side and films converted to crystalline form. The morphology of the nanoparticles films was studied by atomic force microscopy (AFM) which indicates that the average grain size of CdS thin film is in the range of (41.3-44.2-51.6-50.08) nm. The roughness of films surface increases with increasing the sputtering time, which can be useful for the solar cell.

Structural, morphological, electrical and optical properties of amorphous InxAl1-xN thin films for photovoltaic applications

The indium and aluminum nitride (InxAl1-xN) semiconductor material was postulated in 2008 as an excellent candidate to produce solar cells. In this research, amorphous layers of InxAl1-xN (0.55 ≤ x ≤ 0.60) were synthesized using the RF sputtering magnetron technique, and then studied for their possible use in photovoltaic applications. Physical, structural, morphological, optical, and electrical properties were studied. The amorphousness was checked by XRD difractograms. Samples have very smooth surfaces, with very low roughness values, according to AFM and SEM techniques.Electrical properties of the InAlN films were studied using Van Der Pauw technique and Hall Effect parameters. The volumetric carrier concentration decreases when InN fraction mole increases. The mobility values range between 6 × 10−2 and 5 × 10−1 cm2 V−1 s−1, which are lower than those obtained for crystalline and polycrystalline samples. The obtained band gap values could be used in both the absorbing layer and the window layer in solar cells (1.9 eV–2.3 eV). Interestingly, this figures of Eg are very close to the previously obtained values for polycrystalline samples. The optical absorption coefficients were high compared to the materials currently used in solar cells (~105 cm−1). This implies the possibility of using thinner layers in photovoltaic devices based on InxAl1-xN.

Deposition and characterization of spin-coated n-type ZnO thin film for potential window layer of solar cell

Spin-coating technique has been utilized to deposit ZnO thin films on ITO substrates. The dependence of the structural, optical, and electrical properties of the prepared films on both the sol–pH values and annealing temperatures has been investigated. X-ray diffraction analysis has revealed that the optimal sol–pH value was found to be 8 at annealing temperature 450 °C. At these conditions, the optical transmission and reflection data have also shown a clear enhancement in both the morphology and the grain size of the films. In addition, the analysis of I–V and C–V measurements of the Schottky Au/ZnO diode has shown a high agreement with both the investigated structural and optical properties. Furthermore, a new empirical method based on the calculated electrical parameters in the context of both the thermionic emission and Mott–Schottky models has been proposed to evaluate the approximate value of the electron effective mass in the conduction band of the ZnO (m* = 0.224 mo).

Analysis of spray pyrolysed copper zinc sulfide thin films using photoluminescence

Copper zinc sulfide (CuZnS) is an upcoming photovoltaic material. The room temperature photoluminescence (PL) study of thin films of this material synthesized using automated chemical spray pyrolysis (CSP) is reported. The PL spectra from CuZnS comprises of a broad emission constituted by multiple peaks. In this work, ratio of intensities of peaks around 660 nm and 550 nm (I660/I550) as a function of copper ion concentration and deposition temperature is studied. The nature of spectra at lower and higher deposition temperatures seem to be significantly different. Existence of mutually interacting but independent Cu and Zn related phases are evident from PL spectra. Lower deposition temperatures favor copper related phases and higher deposition temperatures promote zinc related emissions. PL technique is used as a non-destructive tool in bringing out the potential of the material to be used as an absorber and p-type window layer in solar cell.

Thermal annealing evolution to physical properties of ZnS thin films as buffer layer for solar cell applications

The conventional CdS window layer in solar cells is found to be hazardous for the environment due to toxic nature of the cadmium. Therefore, in order to seek an alternative, a study on effect of post-annealing treatment on physical properties of e-beam evaporated ZnS thin films has been carried out where films of thickness 150 nm were deposited on glass and indium tin oxide (ITO) substrates. The post annealing treatment was performed in air atmosphere within the temperature range from 100 °C to 500 °C. X-ray diffraction analysis reveals that the films on glass substrate are found to be amorphous at low temperature annealing (≤300 °C) while have α-ZnS hexagonal phase (wurtzite structure) at higher annealing. The patterns also show that the possibility of oxidation is increased significantly at temperature 500 °C which leads to decrease in direct band gap from 3.28 eV to 3.18 eV except films annealed at 300 °C (i.e. 3.39 eV). The maximum transmittance is found about 95% as a result of Doppler blue shift while electrical analysis indicated almost ohmic behavior between current and voltage and surface roughness is increased with post-annealing treatment.

Influence of a novel co-doping (Zn + F) on the physical properties of nano structured (1 1 1) oriented CdO thin films applicable for window layer of solar cell

Un-doped and co-doped (Zn + F) cadmium oxide (CdO) thin films were prepared by modified spray pyrolysis technique using a nebulizer on glass substrates kept at 200 °C. They were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), UV-vis spectroscopy, Hall Effect and photoluminescence (PL) respectively. The thin films were having thickness in the range of 520–560 nm. They were well crystalline and displayed high transparency of about >70% in the visible region. It was clearly seen from the SEM photographs that co-doping causes notable changes in the surface morphology. Electrical study exhibited the resistivity of co-doped CdO thin films drastically fell to 1.43 × 10−4 Ω-cm compared with the un-doped CdO thin film. The obtained PL spectra were well corroborated with the structural and optical studies. The high transparency, wide band gap energy and enhanced electrical properties obtained infer that Zn + F co-doped CdO thin films find application in optoelectronic devices, especially in window layer of solar cells.

Growth of nanocrystalline Zn0.75Mg0.25S thin film by solution growth technique and their characterization as a window layer for solar cell

ABSTRACTZn0.75Mg0.25S thin film was grown by solution growth technique. The as-grown thin film was examined to study its structural and optoelectronic properties. The formation of pure ZnMgS/O phase with wurtzite structure was confirmed by XRD. Optical bandgap (∼3.69 eV) was estimated through Tauc's plot obtained from UV-Vis spectroscopic data analysis. The existence of ZnMgS/O phonons was confirmed from the peaks obtained in Raman spectra. The PL spectrum shows band edge near UV emission. Decrease in resistance after light illumination was observed in I-V characteristics results in 98% photosensitivity.

Effect of iron doping on structural and optical properties of TiO2thin film by sol–gel routed spin coating technique

Thin films of iron (Fe)-doped titanium dioxide (Fe:TiO[Formula: see text] were prepared by sol–gel spin coating technique and further calcined at 450[Formula: see text]C. The structural and optical properties of Fe-doped TiO2thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–vis) and atomic force microscopic (AFM) techniques. The XRD results confirm the nanostructured TiO2thin films having crystalline nature with anatase phase. The characterization results show that the calcined thin films having high crystallinity and the effect of iron substitution lead to decreased crystallinity. The SEM investigations of Fe-doped TiO2films also gave evidence that the films were continuous spherical shaped particles with a nanometric range of grain size and film was porous in nature. AFM analysis establishes that the uniformity of the TiO2thin film with average roughness values. The optical measurements show that the films having high transparency in the visible region and the optical band gap energy of Fe-doped TiO2film with iron (Fe) decrease with increase in iron content. These important requirements for the Fe:TiO2films are to be used as window layers in solar cells.

Highly transparent ZnS buffer layer prepared by ultrasonic spray pyrolysis for photovoltaic applications

Zinc sulfide thin films are deposited by ultrasonic spray pyrolysis. The substrate temperature and sulfur concentrations are varied to attain suitable property for the application as window layer in solar cells. Films prepared at lower temperature have traces of ZnO phase together with the dominant cubic ZnS phase. At 400°C with Zn/S ratio of 1/1.5, sample exhibited higher transmittance (∼86%) consistently in the visible region. With an increase in the sulfur concentration transmittance reduced to ∼50%. Band gap varied from 3.5 to 3.8eV in the films. The existence of single phase ZnS is confirmed through XPS analysis of the optimized sample. 0.5% efficiency is obtained for AgInS2/ZnS solar cells with the optimized ZnS film.