CdS Layer Research Articles

Two dimensional CdS/ZnO type-II heterostructure used for photocatalytic water-splitting

The electronic structures of two dimensional (2D) CdS/ZnO heterostructure (CdZnHT) consisting of CdS singlelayer (SL) and ZnO SL are explored based on hybrid density functional calculation. The negative interface formation energies suggest the formation of CdZnHT is exothermic. The bandgap of CdZnHT is favorable for absorbing visible light, and the decent band edge position makes it thermodynamically feasible for spontaneous generation of oxygen and hydrogen. The formed electric field across the interface induced by charge transfer will reduce photogenerated carrier recombination and promote carrier migration. Particularly, CdZnHT is a type-II heterostructure. Oxygen generation takes place at ZnO layer and hydrogen production occurs at CdS layer, which will also promote the effective separation and migration of phogogenerated carriers and enhance photocatalytic performance. These findings suggest that 2D CdZnHTs are possible candidates as water-splitting photocatalysts.

A 9% efficiency of flexible Mo-foil-based Cu2ZnSn(S, Se)4 solar cells by improving CdS buffer layer and heterojunction interface* *Project supported by the National Natural Science Foundation of China (Grant Nos. 62074037, 61574038, 51961165108, and 51972332), the Natural Science Foundation of Fujian Province, China (Grant No. 2017J01503), the Education and Scientific Research Project of Fujian Province, China (Grant No. JAT190010), the

Flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells show great potential applications due to low-cost, nontoxicity, and stability. The device performances under an especial open circuit voltage (V OC) are limited by the defect recombination of CZTSSe/CdS heterojunction interface. We improve the deposition technique to obtain compact CdS layers without any pinholes for flexible CZTSSe solar cells on Mo foils. The efficiency of the device is improved from 5.7% to 6.86% by highquality junction interface. Furthermore, aiming at the S loss of CdS film, the S source concentration in deposition process is investigated to passivate the defects and improve the CdS film quality. The flexible Mo-foil-based CZTSSe solar cells are obtained to possess a 9.05% efficiency with a V OC of 0.44 V at an optimized S source concentration of 0.68 mol/L. Systematic physical measurements indicate that the S source control can effectively suppress the interface recombination and reduce the V OC deficit. For the CZTSSe device bending characteristics, the device efficiency is almost constant after 1000 bends, manifesting that the CZTSSe device has an excellent mechanical flexibility. The effective improvement strategy of CdS deposition is expected to provide a new perspective for promoting the conversion efficiency of CZTSSe solar cells.

Preparation and Characterization of CdS/CdTe Device for Radiation Sensing

Several Techniques had been applied to measure Ionizing Radiation. Majority of thistechniques are costly and very complicated. We focus on this research to chemically deposition of CdS to formwith CdTe junction x-ray sensor. CdTe has been electrodeposited onto CdS/FTO glass substrate to formwith previously fabricated CdS layer 4 µm thickness. The optimum potential for CdTe deposition hasbeen studied by potentiostat measurement, it shows that -1.3 is the optimum working potential. The XRDanalysis showed that the CdTe films have highly oriented crystallites with the cubic phase zinc blend withpreferred orientation (111). The band gap Eg extrapolated to be 1.4 eV. Four stacked sensors wereconnected in series to measure the device performance. It was observed that amplitude of the pulseformed due to exposed FTO/CdS/CdTe/Mo detector to X-ray of 33 keV and 1mA intensity is 1.03 V.

RF/DC Magnetron Sputtering Deposition of Thin Layers for Solar Cell Fabrication

Thin film Cu(In,Ga)Se2 (CIGS)-based solar cells with relatively high efficiency and low material usage might become a promising alternative for crystalline silicon technology. The most challenging task nowadays is to decrease the PV module fabrication costs by application of easily scalable industrial process. One of the possible solutions is the usage of magnetron sputtering system for deposition of all structures applied in CIGS-based photovoltaic device. The main object of these studies was fabrication and characterization of thin films deposited by sputtering technique. Structural and electrical properties of the sputtered films were analyzed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray Powder Diffraction (XRD), and four-point probe resistivity measurements. The presented findings revealed technological parameters for which sheet resistance of molybdenum (Mo) back contact decreased up to 0.3 Ω/□ and to even 0.08 Ω/□ in case of aluminum layer. EDS analysis provided evidence for the appropriate stoichiometry of CIGS absorber (with CGI and GGI equal to 0.96 and 0.2, respectively). XRD characterization confirmed high-quality chalcopyrite polycrystalline structure of Cu(In,Ga)Se2 film fabricated at relatively low substrate temperature of 400 °C. Characteristic XRD peaks of hexagonal-oriented structures of sputtered CdS and i-ZnO layers were noticed.

Superstrate type CZTS solar cell with all solution processed functional layers at low temperature

A new molecular precursor for Cu2ZnSnS4 (CZTS) has been explored for the fabrication of efficient superstrate type solar cells with all solution processed functional layers at low temperature. The CZTS film made at low temperature (250 °C), without sulfurization was employed in the heterojunction device with a thin interface layer of CdS and the one-step hydrothermally processed rutile TiO2 nanorod arrays. The quality of the CZTS film was optimized by varying the composition of Cu and Zn in the precursor solution. Initial devices with (FTO/TiO2/CdS/CZTS/Au) structure exhibited the power conversion efficiency up to 1.04%, on par with the best in the relevant literature.

MORPHOLOGICAL, STRUCTURAL AND OPTICAL CHARACTERIZATIONS OF Zn-DOPED CdS BUFFER LAYER ELABORATED BY CHEMICAL BATH DEPOSITION

Zn-doped CdS layers, with various percentage ratios [Formula: see text] (= [Zn[Formula: see text]]/[Cd[Formula: see text]]%) were grown on glass substrates by chemical bath deposition (CBD). The effect of Zn-doping on different properties of CdS is studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis and UV-visible diffuse reflectance. The XRD patterns indicated polycrystalline films with (111) orientation and the insertion of Zn does not change the crystallinity of CdS. The Raman spectra show one major peak centered around 300[Formula: see text]cm[Formula: see text] assigned to the first-order longitudinal optic (LO) phonon modes of CdS. The surface morphology visualized by AFM and SEM analysis showed the influence of the Zn-doping on the morphology of the films, the surface roughness is found to decrease from 16.5 to 8.9[Formula: see text]nm with augmenting the ratio [Formula: see text] from 0 to 6%. In regard to the SEM analysis, the increase of [Formula: see text] yielded a lower porosity of the film and voids, and the films become more homogeneous. The EDAX spectra confirmed the existence of Zn in the doped samples. The bandgap decreases from 2.44 to 2.37[Formula: see text]eV, while the transmittance increases from 76 to 86% with augmenting the ratio [Formula: see text].

Improvement of conduction band offset and efficiency of Cu2ZnSn(S,Se)4 thin film solar cells by Cd alloying

In this study, a novel strategy for achieving flexible Cd-alloyed Cu2ZnSn(S,Se)4 thin film solar cells is demonstrated by evaporating a CdS layer with different thickness on Cu2ZnSnS4 precursor followed by selenization process. Improved crystalline quality with enlarged grain size was observed through XRD, Raman and SEM measurements. For Cu2CdxZn1-xSn(S,Se)4 thin film with 50 nm CdS alloying layer, a smallest conduction band offset with −0.20 eV was obtained, which relieved the band mismatching problem between CZTSSe and buffer CdS. Besides, the contact angle of absorber showed a clear difference after Cd alloying, decreasing from 67.8° to 41.2° with the gradual increase in x. Finally, the best device performance benefited from the optimal 50 nm CdS alloying layer, featuring a PCE of 4.01%, Voc of 346.30 mV, Jsc of 24.23 mA/cm−2 and FF of 47.71%, which showed a PCE increase of 1.73% than that without Cd alloying.

Microscopic Analysis of Interdiffusion and Void Formation in CdTe(1-x)Sex and CdTe Layers.

The use of CdSe layers has recently emerged as a route to improving CdTe photovoltaics through the formation of a CdTe(1–x)Sex (CST) phase. However, the extent of the Se diffusion and the influence it has on the CdTe grain structure has not been widely investigated. In this study, we used transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD) to investigate the impact of growing CdTe layers on three different window layer structures CdS, CdSe, and CdS/CdSe. We demonstrate that extensive intermixing occurs between CdS, CdSe, and CdTe layers resulting in large voids forming at the front interface, which will degrade device performance. The use of CdS/CdSe bilayer structures leads to the formation of a parasitic CdS(1–x)Sex phase. Following removal of CdS from the cell structure, effective CdTe and CdSe intermixing was achieved. However, the use of sputtered CdSe had limited success in producing Se grading in CST.

A comparative study on generation and recombination process of kesterite CZTS based thin film solar cells for different designs

In this paper, a comparative study on generation and recombination process in different CZTS designs has been carried out in which their performances and band alignment are invistigated. Firstly, CdS/CZTS design has been modeled using the SCAPS-1D. Secondely, new designs have been proposed in which a back surface field (BSF) layer is inserted and CdS layer is replaced by ZnS. The obtained results exhibit a boosted efficiency from 12.03 % to 14.14 % by inserting a BSF layer with a ZnS buffer layer. The analysis of generation and recombination reveals a high recombination in CdS/CZTS interface in comparaison with ZnS/CZTS due to the high density of defect states at the CdS/CZTS interface. BSF increases recombination in P-region. Whereas, it fairly impacts generation process. ZnS/CZTS/BSF design enhances the collection efficiency in short and long wave length regions resulting in higher solar cell performances (VOC =0.89 V, JSC =25.38mA/cm2, FF=62.44 %, η=14.14 %).

Impact of CdS layer thickness on the composition, structure and photovoltaic performance of superstrate CZTSSe solar cells

In this article, we present a systematic investigation of the influence of CdS layer thickness on the structural and compositional properties of CZTSSe films and photovoltaic performance of superstrate solar cell devices. The selenization of the CZTS films results in Cd diffusion into the absorbing layer. This leads to a significant change in the lattice parameters and crystallinity, and also causes the inhomogeneous distribution of S and Se ions along the thickness of the CZTSSe layer and formation of CZCTSSe kesterite phase. Alternatively, an increase in Cd content for a certain amount also leads to the enhancement of the device performance parameters of CZCTSSe films which are attributed to the improved crystallinity, morphology and, possibly, graded band-gap. The achieved power conversion efficiency of 3.3% is among the highest for the spray pyrolysis deposited solid-state CZTSSe solar cells of superstrate architecture.

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.

Absorber composition: A critical parameter for the effectiveness of heat treatments in chalcopyrite solar cells

AbstractPost‐device heat treatment (HT) in chalcopyrite [Cu (In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown under Cu‐poor conditions but not under Cu excess. We present a systematic study to understand the effects of HT on CuInSe2 and CuInS2 solar cells. The study is performed for CuInSe2 solar cells grown under Cu‐rich and Cu‐poor chemical potential prepared with both CdS and Zn(O,S) buffer layers. In addition, we also study Cu‐rich CuInS2 solar cells prepared with the suitable Zn(O,S) buffer layer. For Cu‐poor selenide device, low‐temperature HT leads to passivation of bulk, whereas in Cu‐rich devices, no such passivation was observed. The Cu‐rich devices are hampered by a large shunt. The HT decreases shunt resistance in Cu‐rich selenides, whereas it increases shunt resistance in Cu‐rich sulfides. The origin of these changes in device performance was investigated with capacitance–voltage measurement, which shows the considerable decrease in carrier concentration with HT in Cu‐poor CuInSe2, and temperature‐dependent current–voltage measurements show the presence of barrier for minority carriers. Together with numerical simulations, these findings support a highly doped interfacial p+ layer device model in Cu‐rich selenide absorbers and explain the discrepancy between Cu‐poor and Cu‐rich device performance. Our findings provide insights into how the same treatment can have a completely different effect on the device depending on the composition of the absorber.

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.

Facile fabrication of well-performing CdS/CdSe quantum dot sensitized solar cells through a fast and effective formation of the CdSe nanocrystalline layer

In this study a co-sensitization strategy is utilized for fabrication of a simple type of quantum dot sensitized solar cells (QDSCs) with high power conversion efficiency. A transparent layer of hydrothermally grown TiO2 nanocrystals (NCs) was sensitized with CdS and CdSe QDs layers and applied as the photoanode of the cells. The CdS layer was deposited through a successive ionic layer adsorption and reaction (SILAR) approach with optimized number of cycles. The CdSe nanocrystalline layer was also formed by a fast and effective chemical bath deposition (CBD) method for co-sensitization. The CBD time was altered in a short range of 6–15 min while the deposition was well-performed and quality of the CdSe layer was quite acceptable. The ZnS passivating layer was finally over-deposited and photoanodes were applied in conventional structure of QDSCs using polysulfide electrolyte and CuS counter electrodes. The CBD time was optimized to find the best bandgap energy/band edge positions and deposition amount of the CdSe layer for higher energy conversion efficiencies. The best photovoltaic performance was achieved for the QDSC with CdSe co-sensitizing layer deposited at 12 min of the CBD process. This optimized cell demonstrated the photovoltaic parameters of Jsc = 22.2 mA/cm2, Voc = 628 mV, and power conversion efficiency of 6.8%. This efficiency was increased about 172% compared to that of reference cell with just CdS QDs as the light sensitizing layer.

Studying the effect of deposition time on physical properties of CdTe thin films; Influence of CdTe electrical properties on CdS/CdTe heterojunction rectifying behavior

CdTe nanostructured thin films were grown on glass substrates by RF-magnetron sputtering at different deposition time periods (10, 20 and 30 min). The layers were characterized by FESEM, EDAX, XRD, Raman, UV–vis., PL spectra, also Seebeck effect and I–V-T measurements. It is found with increasing the deposition time: the size of cubic phase CdTe nano-grains were gradually increased and the stoichiometry of the layers improved, as consistent with the PL spectra of layers. The synthesized CdTe layers were then put in contact with an optimized CdS layer. The analysis of dark I–V data showed that the electrical properties of CdTe layer has crucial impact on rectifying ration (RR) of the prepared CdS/CdTe heterojunction diodes.

A potential alternative deposition technology for CdS buffer layer in kesterite solar cells via intermittent photochemical deposition

In this work, we have developed a novel intermittent photochemical deposition (IPCD) method to prepare CdS buffer layer on Cu2ZnSn(S,Se)4 (CZTSSe) absorber. Results show that the optimized IPCD-CdS buffer layer is compact and uniform, ensuring a perfect contact with the CZTSSe absorber. Our experiments confirm that CdS can nucleate and grow on conducting substrates via IPCD method with controllable particle sizes. Based on the analyses, an electron assisted deposition mechanism is proposed to give a comprehensive insight into the IPCD process. Furthermore, the assembled CZTSSe solar cells with CdS layers deposited via IPCD deliver a highest photoelectric conversion efficiency (PCE) of 5.82%, which is improved by 22% compared to the ones with CdS layers via continuous PCD. Further analyses suggest that the efficiency improvement could be attributed to the improved band alignment at the heterojunction interface between CdS and CZTSSe layers. Our research provides a new way to improve the PCE for CZTSSe based solar cells via optimized deposition process.

Defect limitations in Cu2ZnSn(S, Se)4 solar cells utilizing an In2S3 buffer layer

Alternative n-type buffer layer such as In2S3 has been proposed as a Cd-free alternative in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this study, optical and electronic characterization techniques together with device analysis and simulation were used to assess nanoparticle-based CZTSSe absorbers and solar cells with CdS and In2S3 buffers. Photoluminescence spectroscopy indicated that CZTSSe absorbers with In2S3 buffer had a lower density of detrimental non-radiative defects and a higher concentration of copper vacancies VCu+, responsible for p-type conductivity in CZTSSe, in comparison to the absorber with CdS buffer. Capacitance–voltage (C–V) measurements revealed that the In2S3 buffer-based CZTSSe devices had a three times higher apparent doping density and a consequently narrower space charge region than devices with a CdS layer. This resulted in poorer collection of photo-generated charge carriers in the near-IR region despite a more favorable band alignment as determined by x-ray photoelectron and inverse photoelectron spectroscopy. The presence of interfacial defect states in In2S3 devices as determined by C–V and biased quantum efficiency measurements is also responsible for the loss in open-circuit voltage compared with reference devices with CdS.

Contribution to sustainable and environmental friendly non-toxic CZTS solar cell with an innovative hybrid buffer layer

Due to non-toxicity and earth abundancy of raw materials, CZTS grabbing the attention of researchers to make it highly efficient and cost-effective solar cell harvesting. Thin-film CZTS based solar cell of higher efficiency reported with conventional CdS layer. Toxicity of Cd influences to reduce the thickness of the CdS buffer layer without compromising with the efficiency. The present paper deals with CdS/In2S3 and CdS/ZnS hybrid buffer layer which is more efficient than the solar cell using only the CdS buffer layer. The reduced thickness of the CdS layer in CZTS/CdS/In2S3/ZnO: Al and CZTS/CdS/ZnS/ZnO: Al structures have been optimized by using SCAPS-1D simulation software. This study reveals that there is an enhancement in the performance of solar cells from η = 15.68% with CdS to η = 16.52% with CdS/In2S3 and η = 15.81% with CdS/ZnS hybrid buffer layer. Variation in PV parameters with a variation of the thickness of the buffer and absorber layer has been optimized. The acceptor density of CZTS/CdS/In2S3 and CZTS/CdS/ZnS was varied and results have been optimized. A numerical study of both structures on the photovoltaic performance of CZTS solar cells has been done by using SCAPS-1D simulation software.

Numerical investigation of CIGS thin-film solar cells

The high efficiency of thin Cu(In1−xGax)Se2 solar cells is investigated using the Atlas SILVACO-TCAD tools. The CIGS model is based on an experimental study and takes into account the physical properties, dimensions, and thicknesses of the different layers. The main features model used consists of the thermionic emission concept that was used to describe the carrier transport model across the buffer/absorber heterojunction. Thermionic emission was found to be an important mechanism for carrier transport across the hetero-interface since it produced a matching behaviour for the cell under study with experimental behaviour, thus validating the considered CIGS model for further investigation. To improve efficiency, magnesium fluoride (MgF2) is used as the preferred anti-reflective coating to maximize the photocurrent from the incident light intensity. The effect of varying the single-layer antireflective coating thickness variation, surface recombination velocity at the hetero-interface between CdS and CIGS layers, absorber thickness variation, and gallium content in the Cu(In1−xGax)Se2 on cell performance are studied under AM 1.5G, 1 sun illumination. The novelty of this research includes the configuration of the p-CIGS/n-CdS cells with thin CIS material used for the back surface field layer to improve efficiency. The result has shown that a cell performance of 25% efficiency can be achieved using a 1 µm thick absorber and an MgF2 anti-reflective layer. This result can further aid the development of ultrathin, flexible, and tandem solar cell devices.

Fabrication of Nanosticks-Like CdS Sensitizer for the Application of Solar Cells.

The novelty of this work is to fabricate the Nanosticks (NSs) like CdS sensitizer on the surface of TiO₂ electrode by chemical bath deposition (CBD) method with a very high vacuum annealed at 350 °C for 30 min. Whereas, nanocrystalline TiO₂ electrodes have been prepared on FTO (SnO₂: F) glass by a spin-coating method with high purity (99.99%, Degussa P25) TiO₂ powder. The surface of the CdS layer has been covered by NSs like structures which are confirmed by the scanning electron microscope image. The 100 nm of platinum-coated FTO substrate and polysulfide-based electrolyte are used to assemble the Grätzel Solar cell (GSC). The performance of solar cell (SC) based on NSs like CdS has been compared with the nanoparticles (NPs) based CdS sensitized SC, where CdS NPs has synthesized by CBD without any post-annealing. The efficiency of NSs like CdS sensitized SC exhibits 2.44%, which is 2 folds of the efficiency of the CdS NPs sensitized SC. The NSs like CdS sensitized SC shows the highest photocurrent 20.24 mA/cm² compared to CdS NPs based SC.