Buffer Layer In Solar Cells Research Articles

Simultaneous engineering of the conductivity and work function of biphenylene via fluorine adsorption

Biphenylene (BP) is a new member of the two-dimensional C nanomaterial family, and successful fabrication of BP offers an excellent opportunity for developing innovative C-based electronics. However, its unusual metallicity critically restricts its applications in field-effect transistors (FETs) and photocatalysis. Simultaneously, its relatively low work function (ϕ, 4.33 eV) seriously restricts its applications in anode materials of electronic devices. Therefore, understanding the tunabilities of electronic properties and ϕ of BP-based nanomaterials is crucial to guide experimental exploration; nevertheless, to date, little attention has been paid to this area. Herein, we theoretically demonstrate that conductivity of fluorinated BP (Fn-BP) evolves in the order metallic → semimetallic → semiconductivity with increasing F concentration, attributed to a bonding transition of BP (sp2 → sp2 + sp3 → sp3). Particularly, ϕ of BP can be significantly improved (4.82–6.97 eV) by fluorination, approximately two-fold higher than that of Fn-graphene owing to p electron transfer between F and BP. Consequently, metallic F2D-BP and semimetallic F4S-BP with favorable ϕs can be utilized as substitutes for Au and Pt anodes, respectively. Specifically, F8D-BP, F16D-BP, and F24D-BP with exceptional band gaps of 0.40, 2.80, and 3.44 eV, respectively, exhibit high potentials for making channel materials in FETs, candidate materials in photocatalysis, and buffer layers in solar cells, respectively.

Numerical analysis of the thin film solar cell modelled based on In doped CdS semiconductor

In this study, pure and 1%, 2% and %3 In-doped CdS thin films were produced by spray pyrolysis method. CdS is an n-type (II-VI group) semiconductor material and used as a buffer layer in solar cells. By doping In into CdS thin film, it was investigated how optical and crystalline behavior of thin film are changed. Using Moss and Herve&Vandamme and Ravindra relations, refractive indices and dielectric coefficients were investigated depending on the band gap of the obtained CdS sample. It has been observed that In element decreases the band gap of CdS thin film, improved its crystal structure and reduced its roughness. Therefore, 3% In doped CdS has gained a more ideal feature for use as an n-type semiconductor in solar cells. CIGS/In doped CdS solar cell was modelled and analysed by SCAPS-1D simulation program by using the physical parameters of the semiconductor layers that make up solar cells as imputs of program. Photovoltaic parameters of solar cell based on donor defect density, the neutral interface defect density and Auger electron/hole capture coefficient which were calculated by using In %3 doped CdS thin film, which has the most ideal n-type semiconductor properties.

A synergistic approach in designing InP/ZnS quantum dot based CIGS solar cell

This research work investigates the implementation of non-toxic InP/ZnS quantum dot (QDs) buffer layer in solar cell. Due to its nontoxic behaviour, it is a better replacement of commonly used CdS buffer layer. InP/ZnS quantum dots buffer layer enhances light absorption, leading to a broader spectral response and improved power conversion efficiency. Graded CIGS (CuIn1-xGaxSe2) is used as absorber layer in this study for better utilization of solar spectrum. The combined utilization of an InP/ZnS QD buffer layer and a graded absorber layer results in a synergistic enhancement of the cell's performance. Further optimization of CIGS layers is achieved by varying the gallium content (x) in the Cu(In1−xGax)Se2. For the gallium content (x) in the range of 0.20 to 0.15, maximum efficiency is achieved which is 31.20 %. Numerical modeling is employed in this study to analyze how variations in thickness, doping concentration, and defect density impact the solar cell performances.

Exploring the effects of ultra-low loading level of silver oxide nanoparticles on the dielectric, I-V characteristics and optical energy band gap of thermoplastic polyurethane and poly-aniline blend nanocomposites

This study deals with the exploration of ultra-low loading levels of Silver oxide (Ag2O) nanoparticles on the materials properties such as dielectric, I-V characteristics, and optical energy band gap of thermoplastic polyurethane (TPU) and Polyaniline (PANI) blend nanocomposites. The nanocomposites with varying loading levels of Ag2O nanoparticles have been fabricated using the most simplified solvent casting technique. The dispersion pattern of the Ag2O phase in the vicinity of the TPU and PANI Matric has been observed from the high-resolution transmission electron microscopic (HRTEM) analysis. The dielectric properties like dielectric permittivity(εʹ), AC conductivity (σac), Nyquist plot, etc., of the fabricated nanocomposites have been explored in a wide range of frequency of the applied electric field (1 -106Hz). The significant improvement in εʹ with a 3 wt% loading level of Ag2O is one of the outstanding findings of today’s research work. The obtained I-V characteristics indicate the formation of dielectric materials with pseudo-metallic behavior. The decrease in optical energy band gap with the addition of Ag2O ensures the suitability of the fabricated nanocomposites to be used in the construction of the solar cell. Dielectric properties ensure the suitability of the materials to be used in the construction of the buffer layer of solar cells and the fabrication of EMI shielding panels to be used in heavy electronics where radiation leakage is very frequent.

Characterization and optimization of ZnS thin film properties synthesis via chemical bath deposition method for solar cell buffer layer

Zinc Sulphide is one of most studied semiconductor with wide band gap (3.5–3.9 eV) versatile material due to its physical and chemical properties. ZnS is a non-toxic material and a suitable candidate to be a buffer layer for heterojunction solar cells. In this study, Zinc Sulphide (ZnS) thin films were deposited by chemical bath deposition technique using Zinc Acetate Dihydrate [Zn (CH3COO)2. 2H2O] and Thiourea [CH4N2S]. The ZnS thin films samples were characterized by UV-Vis NIR Spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDX), Fourier-Transform Infrared Spectroscopy (FTIR) and Thin-Film Measurement Instrument. FTIR spectra confirmed the presence of ZnS bond in the crystalline thin film. XRD data confirmed the cubic structure of the deposited thin film only when the amount of Thiourea was increased and the complexing agent Hydrazine Hydrate was replaced with Tri-Sodium Citrate. Crystallite size and strain were estimated using Debye-Scherrer model and Williamson-Hall model and lattice constant was estimated using Nelson-Riley plot. Otherwise, XRD showed the amorphous phase. UV-Vis data confirmed ZnS thin films as enough transmittive and it showed higher bandgap. Thin-Film Measurement Instrument was used to measure the thickness of the ZnS thin films. Synthesized ZnS thin films exhibited promising characteristics for using as the buffer layer of the heterojunction solar cells. Highlights • ZnS thin films were prepared successfully by simple, low cost and environment friendly chemical bath deposition method. • XRD measurement confirmed both Amorphous and Crystalline phase of ZnS thin films. • By changing the precursor only can be achieved crystalline phase from amorphous phase of ZnS thin film. • The amount of precursor and deposition conditions can be optimized to produce crystalline ZnS thin film.

Controllable and innovative preparation of Zn(O,S) buffer layers for CIGS thin film solar cells

The band gap of CdS (Eg = 2.4 eV) was narrow, which made it unable to transmit short-wave sunlight through the CIGS absorber layer. Zn(O,S) thin film, prepared by doping O into ZnS, had a wider band gap, and the raw material was green and non-toxic, making it suitable as a buffer layer for solar cells. However, CBD-Zn(O,S) usually takes longer than CdS deposition. In this work, By shortening the deposition time through the fast hydrolysis of TAA. Na3NTA was added in the solutions to improve the quality of Zn(O,S) thin films. The effect of Na3NTA concentration on the complex ion contents was investigated. When Na3NTA was added at a concentration of 0.04 M along with TAA (0.04 M), the film had a high T% of 88.6%, Eg of 3.76 eV, and a dense grain distribution. ZnS and ZnO grew at (111) and (100) crystals, respectively. Raman and XPS analyses showed the existence of Zn–S and Zn–O bonds, indicating the high crystalline quality of the Zn(O,S) thin films prepared with CBD. Finally, when the optimal concentrations of ZnSO4, NH4OH, Na3NTA, and TAA were 0.04 M, 0.48 M, 0.04 M, and 0.04 M, respectively, the prepared Zn(O,S) thin films could be used as a cadmium-free buffer layer for solar cells.

In2S3 vacuum pressure sensor through a simple two-step process

We demonstrate here an In2S3 based vacuum pressure sensor that can operate over a vacuum range, 103–10−3 mbar at room temperature. It is shown that vacuum pressure has a significant electrical impact on the sensitivity and the sensor response of the device. The sensor response of the device in terms of the rate of resistance change is 183 with a quick rise/fall time of 3.3/1.7 s. Even after being exposed to ambient conditions for 8 weeks, the device displays a consistent and periodic sensor response for 100 consecutive vacuum on/off cycles, demonstrating its durability. X-ray photoelectron spectroscopy was used to identify the surface adsorbed/chemisorbed groups, which are responsible for vacuum sensing properties. These surface effects were further confirmed by exposing the device to different environments such as humidity, high temperature, and high purity oxygen. Though In2S3 is known for its properties as a buffer layer in solar cells, this study reveals another potential application of In2S3 thin films as a vacuum pressure sensor.

Extreme learning machine computational method of modeling energy gap of doped zinc selenide nano-material semiconductor

Zinc selenide (ZnSe) semiconductor belongs to a class of wide energy gap material with low visible region optical absorption, high optical coefficient (nonlinear) and fascinating optoelectronic as well as photocatalytic features which foster and strengthen its applications in resisting thermal shock, photoelectric fields (which include dielectric mirrors, shot wavelength lasers and light emitting diode), buffer layer of solar cell and many photocatalytic environmental cleanliness applications. Nanostructured ZnSe semiconductors occupy a special place in application domain due to the characteristic features attached to the crystallite size of the material which include high fluorescence quantum yields, solvent dispersibility and adjustable emission color among others. Effective utilization of nanostructured ZnSe semiconductor involves tuning of its energy gap through doping mechanisms which is accompanied with distortion in the parent lattice structure. In this contribution, extreme learning machine (ELM) computational intelligent method is proposed for predicting the band gap energy of doped ZnSe nanostructured semiconductor using the material crystallite size and lattice parameter as descriptors to the models. The developed ELM based model using sine (Sine), sigmoid (Sig) and transig (Trang) activation functions were compared with the existing SVR-GA and SPR models in the literature using various performance metrics. The developed Sine-ELM model shows superior performance over Sig-ELM, Trang-ELM, SVR-GA (2021) and SPR (2021) models with performance improvement of 12.74%, 64.89%, 68.87% and 75.62% using mean squared error (MSE) metric for testing data samples. The superiority of the model developed was further justified through validation with external set of data. The precision and superiority of the ELM based models developed would eventually ease quick characterization and tuning of energy gap of ZnSe nanostructured semiconductors for various applications.

Analysis of different vacuum annealing levels for ZnSe thin films as potential buffer layer for solar cells

Analysis of different vacuum annealing levels for ZnSe thin films as potential buffer layer for solar cells

Effect of concentration of cadmium sulfate solution on structural, optical and electric properties of Cd1–x Zn x S thin films

Cd1– x Zn x S thin films were deposited by chemical bath deposition (CBD) on the glass substrate to study the influence of cadmium sulfate concentration on the structural characteristics of the thin film. The SEM results show that the thin film surfaces under the cadmium sulfate concentration of 0.005 M exhibit better compactness and uniformity. The distribution diagrams of thin film elements illustrate the film growth rate changes on the trend of the increase, decrease, and increase with the increase of cadmium sulfate concentration. XRD studies exhibit the crystal structure of the film is the hexagonal phase, and there are obvious diffraction peaks and better crystallinity when the concentration is 0.005 M. Spectrophotometer test results demonstrate that the relationship between zinc content x and optical band gap value E g can be expressed by the equation E g(x) = 0.59x 2 + 0.69x + 2.43. Increasing the zinc content can increase the optical band gap, and the absorbance of the thin film can be improved by decreasing the cadmium sulfate concentration, however, all of them have good transmittance. At a concentration of 0.005 M, the thin film has good absorbance in the 300–800 nm range, 80% transmittance, and band gap value of 3.24 eV, which is suitable for use as a buffer layer for solar cells.

The Effect of the Deposition Method on the Structural and Optical Properties of ZnS Thin Films

ZnS is a wide band gap material which was proposed as a possible candidate to replace CdS as a buffer layer in solar cells. However, the structural and optical properties are influenced by the deposition method. ZnS thin films were prepared using magnetron sputtering (MS), pulsed laser deposition (PLD), and a combined deposition technique that uses the same bulk target for sputtering and PLD at the same time, named MSPLD. The compositional, structural, and optical properties of the as-deposited and annealed films were inferred from Rutherford backscattering spectrometry, X-ray diffraction, X-ray reflectometry, Raman spectroscopy, and spectroscopic ellipsometry. PLD leads to the best stoichiometric transfer from target to substrate, MS makes fully amorphous films, whereas MSPLD facilitates obtaining the densest films. The study reveals that the band gap is only slightly influenced by the deposition method, or by annealing, which is encouraging for photovoltaic applications. However, sulphur vacancies contribute to lowering the bandgap and therefore should be controlled. Moreover, the results add valuable information towards the understanding of ZnS polymorphism. The combined MSPLD method offers several advantages such as an increased deposition rate and the possibility to tune the optical properties of the obtained thin films.

Reduction of bandgap of ITO film and possibility of use as a window layer by incorporation of copper

We report on reduction of the bandgap energy of ITO films by incorporation of copper along with thermal annealing for use as a window layer in optoelectronic applications such as solar cells. Using a conventional solid state reaction method, high purity In2O3 and SnO2 (99.99%) powders were mixed in a mass ratio of 75:25 in a ball milling for about one hour to fabricate ITO alloys. Electron beam evaporation was used to prepare an an ITO film with thickness of about 165 nm on a glass substrate. By immersing the films in a solution of Cu(NO3)2 (1g/1000ml) for 30 min, the prepared films were doped by ion exchange with Cu. Furthermore, the doped films were annealed in air at different temperatures for the diffusion of dopant Cu content (100, 150, 200, 250 and 300 oC) for 30 min. The (EDAX) was used to set the initial treatment composition. The XRD pattern was used to identify the cubic phase of the ITO films. Using spectroscopic ellipsomerty, the film thickness, refractive index as well as extinction coefficient of the film was determined in terms of a three layers model. We show that the refractive index and extinction coefficient increase with incorporation of Cu and the annealing temperature. The possible transition in the as deposited and annealed films were found to allow direct transitions with reduction of the band gap energy from 3.50 to 2.75 eV with the increase of the annealing temperature. This means that the lower layer of ITO behaves as a window layer and is a shallow layer available as a buffer layer of solar cell.

Tuning the electronic band structure and optoelectrical characteristics of ALD-grown Zn(O,S) buffer layers for SnS solar cells

Conduction band offset (CBO) is an important aspect in the development of SnS-based solar cells. Studies on buffer layers are needed to obtain a CBO that matches the SnS absorber layer. Zn(O,S) is a promising cadmium sulfide replacement for a thin film solar cell buffer layer due to its non-toxicity and large band gap, and its film characteristics can be optimized by adjusting the oxygen and sulfur ratio. However, very few studies have been conducted on processed Zn(O,S) film’s electronic band structure, and the absence is more serious for the case of atomic layer deposition (ALD) method. In this study, we deposited Zn(O,S) films with various ZnO/ZnS cycle ratios using the ALD supercycle method and identified their film characteristics and electronic band structures. Results showed that the Zn(O,S) films had high concentrations of ZnS compared to the ZnS cycle fraction. Mixing the ZnO and ZnS cycles reduced the film’s crystallinity and affected the Zn(O,S) films characteristics. Further, the electronic band structures were identified using UV–vis and UPS analysis. The Zn(O,S) films using 14:1 and 19:1 ZnO/ZnS cycle ratios showed an ideal flat CBO with SnS absorber.

Enhanced electrical properties of Te-enriched ZnTe thin films for buffer layer in solar cell

Zinc Telluride (ZnTe) powder of 99.9% purity was used to deposit ZnTe thin films on ultra-sonically cleaned slides of glass. A locally manufactured Closed Space Sublimation (CSS) technique was used to deposit these thin films. As-deposited ZnTe thin films were further exposed to tellurium (Te) for different deposition times under high vacuum. Annealing was carried out after the deposition of Tellurium (Te) on as-deposited ZnTe thin films for diffusion of Te into ZnTe thin films. Cubic phases were found before and after enrichment of Te into as-deposited ZnTe thin films via X-ray Diffraction (XRD) studies. Preferred orientation was [111] and the crystallite size increased after enrichment of Te. The surface morphology was studied using scanning electron microscopy (SEM) which confirmed that grain sizes significantly increased after the enrichment of Te into ZnTe thin films. Energy dispersive X-rays (EDX) confirmed the elemental composition of zinc (Zn) and tellurium (Te). The transmittance decreased after the enrichment of Te into ZnTe thin films. A small change in energy band gap was calculated using Tauc relation. Hall measurement was carried out to study the electrical behavior of Te-enriched ZnTe thin films and found that electrical resistivity of as-deposited ZnTe thin films was of the order of 106 Ω-cm. The electrical resistivity reduced to 104 Ω-cm after Te enrichment. X-rays photoelectron spectroscopy (XPS) study was carried out to check the chemical bonding and states before and after Te-enrichment. Te-enriched ZnTe thin films showed better properties and found suitable for buffer layer of II generation solar cells.

Features of a ZnxCd1 – xS Buffer Layer for Use in Thin-Film Solar Cells in the Context of a Literature Review

The paper presents a literature review of the latest achievements in the creation of highly efficient thin-film solar cells (SCs) based on multicomponent polycrystalline materials: semiconductors of the AIIBVI groups of the periodic table, cadmium telluride (CdTe) and a three-component compound AIBIIICVI copper–indium–gallium and selenium (Cu (In, Ga)Se2). The main criteria for the selection of the buffer layer material for thin-film SCs based on CdTe and Cu (In, Ga)Se2 are analyzed. The values of the main output parameters of the load current–voltage characteristic (short-circuit current, open-circuit voltage, fill factor of a light current–voltage characteristic, efficiency) of high-performance SCs based on CdTe and Cu(In, Ga)Se2, which have been achieved to date, are presented. The spectral photosensitivity of a SC in the short-wave region of the electromagnetic spectrum is determined by the band gap width and thickness of the p–n transition frontal–buffer layer. An increase in the photosensitivity in the short-wave spectrum part of electromagnetic radiation is achieved by an increase in the band gap of the buffer layer. In this case, it is necessary to take into account the important energy (energy of electron affinity) and crystallographic (crystal lattice parameter) parameters of the semiconductor material. As one of the promising materials for the buffer layer, semiconductor polycrystalline layers from the AIIBVI class, semiconductor chemical ternary compounds ZnxCd1 – xS, in which Eg varies from 2.4 eV (x = 0, CdS) to 3.6 eV (x = 1, ZnS) are proposed. An analysis of the compatibility of ZnxCd1 – xS layers with different x values, as a buffer layer for SCs based on CdTe and Cu(In, Ga)Se2, is carried out. Possible scenarios of variation in the main output parameters of SCs, such as short-circuit current and open-circuit voltage, are analyzed.

Impact of different annealing conditions on physical properties of ZnSe thin films for ecofriendly buffer layer applications

In Cd-based and CIGS solar cells, the CdS is used as optical window to ensure maximum transmittance of the incident irradiance towards absorber-layer while Cadmium free viable alternative is required to replace toxic CdS layer. Herein, ZnSe films of thickness 200 nm were prepared by electron-beam evaporation followed by annealing in air ambient and vacuum within temperature range 100−300 °C and then subjected to various characterization tools to optimize physical properties for buffer layer applications. The structural properties demonstrate Zinc blende cubic structure with preferred reflection corresponding to (111) plane. The optical properties reveal to high transmittance in visible and nearly IR regions and direct energy band-gap is estimated within 2.53–2.65 eV range. The surface morphology indicates uniform deposition with grain-growth, EDS analysis confirms deposition of films and current-voltage relation indicates ohmic behavior. The findings warrant for applying films air annealed at 300 °C as potential buffer-layer in solar cells.

Achieving desired quality of ZnS buffer layer by optimization using air annealing for solar cell applications

The possibility of maximum transmittance at lower thickness of light transmitting ZnS layer and its optimization by air-annealing as an alternative to hazardous and expensive CdS is reported in this communication in order to achieve better buffer layer for solar cells. Thin films of ZnS were deposited using e-beam evaporation on glass and ITO substrates and subjected to air-annealing followed by characterizations for physical properties. XRD patterns revealed amorphous behavior which transformed into cubic (111) plane with change of substrate and annealing whereas surface topography reveals hill and deep valley like structures. Optimal transmittance of maximum 95% in visible region, direct band gap of 3.38 eV and maximum electrical conductivity were observed for 200°C annealed films. The study refers that films annealed at 200°C are claimed to be suitable for buffer layer applications.

Impact of Hydrogen flow rate on physical properties of ZnS thin films: As potential buffer layer in solar cells

The exceptional need of potential Cd-free buffer layer in thin film solar cell devices motivated us to study the role of post-deposition Hydrogen annealing for the optimization of physical properties of ZnS thin films. The deposited films of thickness 200 nm were hydrogenated within the flow rate range of 50.0–150.0 sccm at 200 °C. XRD analysis revealed transformation of amorphous into cubic phase with maximum crystallinity at 150.0 sccm for films deposited on glass substrate while into wurtzite structure for films on ITO substrate with enhanced crystallinity. A mixed phase (cubic and hexagonal) at 150.0 sccm also appeared. Electrical behaviour (I–V) exhibits ohmic nature with maximum carrier concentration at 100.0 sccm. The blue shift in absorption edge and maximum of 95% transmittance were recorded in the visible region with optical energy band gap of 3.41 eV at 150.0 sccm. The reduction in surface roughness is observed in surface topographical analysis while the photoluminescence (PL) study indicated a sharp peak at 2.95 eV with strongest emission for 150.0 sccm attributed to reduction of defects at interstitial sites and passivation of grain boundaries. These results are useful to understand the Hydrogen related impurities in ZnS films and the improvement caused by hydrogenation to physical properties suited for buffer layer in solar cells.

Characterization of spray deposited ternary ZnSxSe(1-x) thin films for solar cell buffers

This paper reports on cadmium free, environment friendly, industrially beneficial, chemically sprayed ZnSxSe(1-x) (ZSS) thin films with tunable band gap which is suitable for various optoelectronic applications including buffer layer in solar cells. Chemically sprayed ZSS thin films with x ranging from 0 to 1 were studied extensively by adopting the characterization techniques like X-ray diffractometry (XRD), Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDAX), Ultraviolet – visible (UV–VIS), Photoluminescence (PL) and Raman spectroscopies in order to assess the suitability of the formed thin film for the buffer layer applications. XRD analysis was done to determine various parameters like lattice constant, crystallite size, strain and dislocation density. From lattice constant, Vegard's law was also verified and compared the composition estimation with EDAX data. Refractive index was compared using Vandemme model with the values obtained using reflectance data. Photoluminescence and Raman spectra were analyzed to get an insight on structural defects, which have major role in deciding the electrical properties. Electrical properties were assessed by estimating carrier concentration, carrier mobility and electrical resistivity by adopting Van der Pauw technique. Based on structural, optical and electrical properties, sample with x = 0.4 is suggested for the buffer layer application in CIGS based solar cells, which produces minimum lattice mismatch with considerably high optical transmittance and electrical conductance.

Comparative studies of CdS thin films by chemical bath deposition techniques as a buffer layer for solar cell applications

Cadmium sulfide (CdS) buffer layer that decouples the absorber layer and window layer in thin-film solar cells was synthesized by two different chemical bath deposition (CBD) techniques with varying deposition parameters. X-ray diffraction (XRD) revealed that the CdS thin film crystallizes in a stable hexagonal wurtzite structure having a preferential orientation along (002) reflection plane with a crystallite size varying from 20 to 40 nm. First longitudinal optical phonon mode was identified at Raman shift of 305 cm−1. Uniform, granular, continuous, and smooth surface with an average grain sizes (< 100 nm) as well as small roughness (< 9 nm) was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The symmetric composition of cadmium and sulfur along with larger grains (20 nm) was observed at higher deposition temperatures and times. The optical band gap of CdS samples obtained from process one was in the range of 2.3–2.35 eV, while the band gap by the second CBD process lay in between 2.49 and 2.65 eV, showing the most stable compound of CdS. The presence of a green emission band in photoluminescence spectra (PL) demonstrated that the CdS material has better crystallinity with minimum defect density. Hall effect studies revealed the n-type conductivity of CdS thin films with a carrier concentration values in the order of 1016 cm−3. Furthermore, CdS thin films fabricated by CBD process exposed better quality that might be more suitable material as a buffer layer for thin-film solar cells.