Conference Papers
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/28506
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Item Numerical analysis of CZTSSe solar cell with different BSF layers for performance improvement(SPIE, 2021) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.This work reports the performance improvement of the CZTSSe solar cell by using a back surface field (BSF) layer between the back contact and absorber layer. Firstly, a cell model with Cadmium (Cd) free buffer structure (Mo/CZTSSe/Zn(O, S)/ZnO/ITO) is developed using SCAPS-1D software. To improve the performance, thickness and composition ratio of the absorber (CZTSSe) and buffer (Zn(O, S)) layer are optimized through simulations. The efficiency of 14.39% is achieved for a Sulphur content of 40% and 70% in CZT(SxSe1-x)4 and Zn(O1-x Sx) respectively. Further performance improvement is attempted by using a back surface field (BSF) layer between the back contact and the CZTSSe absorber layer. The P+-MoSe2, P+ - Si0.75Ge0.25, and SnSe layers are used as BSF layers to investigate their effects on performance improvement. Inclusion of the BSF layer gives further scope for optimization of the absorber layer thickness. It is observed that the use of SnSe as a BSF layer produces maximum power conversion efficiency of 17%. These findings will be helpful for the research community working in the area of high-performance and low-cost CZTSSe based solar cells. © 2021 SPIE.Item Doping of ZnMgO with phosphorus by spin-on dopant technique(SPIE, 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.Zinc magnesium oxide is a ternary compound wide bandgap semiconductor. Incorporation of Mg into ZnO helps in increasing the of p-type conductivity by affecting the background n-type nature of ZnO. This is possible because Mg incorporation in ZnO elevates the conduction band edge which in turn increases the distance between the shallow donor level and conduction band minima, resulting increase of activation energy for background donor. In this work, we report Spin-on Dopant technique to dope phosphorus in Zn0.85Mg0.15O lattice. The undoped ZnMgO thin film (sample A) was deposited using RF sputtering. The SOD sample (sample B) was prepared using P509 spin on dopant and kept approximate 1cm above ZnMgO film at 600°C for four hours. The doped sample was annealed at temperature 700°C (sample C) in oxygen ambient to see the high temperature annealing effect on doping. In studies of high-resolution x-ray diffraction, a dominant (002) peak was observed in sample A, B, and C at 34.173°, 34.624°, and 34.638° respectively. The shifting of (002) peak at higher angle for doped samples indicates the phosphorus doping in film. The XPS spectra of phosphorus 2p peak are appears at ∼134 eV indicates the presence of P atoms as P-O bonds in ZnMgO lattice. The Donor-Acceptor pair (DAP) transition peak around 3.473eV and free Acceptor (AX°) peak around 3.588eV were found in photoluminescence spectra of sample B revels the phosphorus doping in ZnMgO. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.Item Improvement in optical and elemental properties of spin-on phosphorus doped ZnO film(SPIE, 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.SOD is a type of conventional doping technique where diffusion of dopant atom takes place from the liquid source to film by thermal annealing of sample. The study shows the SOD process is a cost effective, less destructive and an efficient way to dope ZnO film. We have doped ZnO films with phosphorus atom by simply annealing it in atmospheric furnace up to 600°C for 4 hrs. After in-situ annealing SOD process, sample has also been ex-situ annealed at 900°C in oxygen ambient for 10 secs. The elemental analysis of phosphorus 2p peak at 132.62 eV ensures the existence of P-O bond for doped sample which shows phosphorus replacing Zn and bonding with oxygen in to the lattice in order to make Pzn-2Vzn an acceptor complex. The doped samples showed the photoluminescence peak at 3.32eV and 3.35eV, which attributed to free electron to acceptor (FA) and acceptor-bound exciton (A0X) energy as an evidence of acceptor doping in ZnO film. The ex-situ annealing of doped sample further improves in passivation of deep level defects of film. All sample has (002) orientation, and a compressive stress to be found in the doped sample due to phosphorus replacing Zn, are confirmed by analysis of XRD results. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.Item Improvement in performance of CZTSSe solar cell by using cadmium free buffer layers(SPIE, 2021) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.Cadmium Sulphide(CdS) has been the most preferred n-type buffer layer and Indium Tin Oxide(ITO) is the popular window layer in kesterite solar cells. Cadmium being toxic and Indium being a rare earth element, continuous efforts are being made to replace these materials from kesterite solar cells structure. In this work, ZnS, ZnSe, and Zn0.8Sn0.2O are considered as possible alternatives for CdS. Similarly, Aluminium doped Zinc Oxide(AZO) is considered as an alternative for ITO. Firstly, a cell model with CdS and ITO (Mo/CZTSSe/CdS/ZnO/ITO) is developed using SCAPS-1D software. To optimise the performance parameters namely open-circuit voltage(Voc), short-circuit current density(Jsc), fill factor(FF), and the power conversion efficiency (PCE) for irradiation under normal working conditions, thickness and the composition ratio of the absorber layer(CZTSSe) are evaluated through numerical simulations. PCE of 14.51% is achieved for a 40% of Sulphur content and 2 um thickness of Cu2ZnSn(SxSe1-x)4 when CdS is used as the buffer layer. For the same structure, replacing ITO with AZO results in a PCE of 14.62%. Use of Cadmium-free buffer layers ZnS, ZnSe, and Zn0.82Sn0.18O with ITO as window layer result in PCE of 13.98%, 14.28%, and 14.53%, respectively. For the Cadmium-free buffer layers, an improvement in PCE is achieved when ITO is replaced by AZO, with the highest being 14.62% for Zn0.82Sn0.18O. This can be attributed to the smaller conduction band offset, which reduces the recombination of photogenerated carriers and improves the carrier transport in the solar cell. The above results indicate that the Zn0.8Sn0.2O and AZO can be potential candidates for the buffer layer and window layer, respectively, for high-performance and cheap kesterite solar cells. © 2021 SPIE.Item Simulation and optimization of nanostructure incorporated CZTS solar cell towards higher performance(SPIE, 2022) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.Kesterite solar cells require a novel high-research implementation to replace the costlier Copper Indium Gallium Selenide (CIGS) solar cells. This study, attempts to demonstrate the performance improvement of kesterite solar cells using multiple quantum wells (MQWs). A numerical simulation approach using Atlas software from Silvaco is used. Firstly, a baseline model of the best performing Cu2ZnSnS4(CZTS) solar cell Mo/CZTS/CdS/i-ZnO/ITO with 11% power conversion efficiency (PCE) is implemented. Further, to exploit the use of MQWs, Cu2ZnSn(SxSe1-x)4 (CZTSSe) with 40% sulfur content is added as well material in a series of wells while keeping the CZTS as the barrier material. This structural modification facilitates the absorption of lower energy photons by the lower bandgap well material. Further, MQW induced quantized energy levels and higher electric fields help to increase the carrier collection, thereby increasing the solar cell's short circuit current density (Jsc) and overall power conversion efficiency (PCE). A detailed study on the effect of well and barrier thickness on the solar cell performance is done, and a well thickness of 5 nm and a barrier thickness of 10 nm was chosen for further optimization. The number of wells is also optimized to 70, which results in the highest performance of the solar cell. This structural modification and optimization remarkably improved Jsc by 48.76% (rel.) and PCE by 34.72% (rel.) compared to solar cells without nanostructures. Moreover, with an optimized structure, an external quantum efficiency (EQE) of over 95% is achieved with the optimized structure. © © 2022 SPIE.Item Effect of post-deposition annealing ambient on Gallium Oxide (Ga2O3) films(SPIE, 2022) Mishra, M.; Saha, R.; Bhowmick, S.; Pandey, S.K.; Chakrabarti, S.Gallium Oxide (Ga2O3) is an emerging wideband semiconductor which can be utilize in solar-blind photodetector and high power electronics application. Having a large bandgap and high breakdown field makes Ga2O3 material suitable for these device applications. However, the physical and the optical properties of Ga2O3 can be tailored by changing the annealing ambient and temperature, and understanding how the annealing atmosphere can affect these properties is crucial for designing a next generation optoelectronic devices. Moreover, the presence of defects and impurities can also affect the device parameters. Thus, in this work, we have investigated the influence of post deposition annealing atmosphere on the morphological, structural, and optical properties of Ga2O3 films. The prepared samples were further went through thermal annealing at 800℃ for 30 mins in Nitrogen (N2), and Oxygen (O2) ambient to achieve β-phase of Ga2O3. The structural properties of all the samples were studied by Atomic force microscopy, and X-ray diffraction while the optical properties were studies by UV-Visible, and photoluminescence spectroscopy. We have found monoclinic β-phase in the polycrystalline annealed Ga2O3 samples. The optical band gap of films were increased after annealing and highest band gap is obtained to 5.44eV in N2 annealed sample as compared to as-deposited sample (4.56eV). A broad photoluminescence spectrum ranged from 350 to 480 nm was observed, which further deconvoluted in three peaks at around 378 nm, 399 nm, and 422 nm in as-deposited sample. The same peaks with broad photoluminescence spectrum was found to be blue shifted for annealed samples as compared to the as-deposited. This study will open a new direction in future deep-UV photodetector fabrication. © 2022 SPIE.Item Reduction of oxygen vacancy related defects in RF sputtered deposited ZnO films by impurity (Phosphorus) incorporation(SPIE, 2022) Mishra, M.; Saha, R.; Bhowmick, S.; Pandey, S.K.; das Gupta, K.D.; Chakrabarti, S.ZnO is a fascinating wide gap (3.37 eV) semiconductor due to its tunable optical and electrical properties, which can be utilized for several nanodevices such as nanogenerators, photodetectors, sensors, lasers, and TFTs. In this study, we have investigated the effect of the incorporation of dopants on the native defects and corresponding optical properties of ZnO. We have prepared three samples for the current study and such samples are named samples Z-0, Z-1, and Z-2 for undoped ZnO film, undoped ZnO film annealed at 800°C, and phosphorus doped ZnO film by using spin-on dopant method at an elevated temperature of 800°C, respectively. The XRD results show a dominant peak along the (002) plane for all samples. The Room-temperature photoluminescence spectra reveal that the broad peak around 542 nm for sample Z-0 gradually shifts towards the UV region for samples Z-1 and Z-2 and appears around 509 nm and 413 nm, respectively. Significantly, such blue emission is associated with the transitions from oxygen vacancies to valence band or zinc interstitial to valance band. Also, relatively huge reductions in oxygen vacancies are observed in phosphorus doped ZnO films as compared with undoped and undoped-anneal films. Further, we have verified such reductions in oxygen vacancies with XPS O-1s spectra-related peaks (~531-532 eV) with high-temperature annealing and phosphorus doping. Therefore, such a type of oxygen vacancy reduction in ZnO films by cost-effective SOD doping technique is highly essential for developing several ZnObased functional devices. © 2022 SPIE.Item Temperature Induced Conductivity Reversal in ZnO Thin Films(SPIE, 2023) Mishra, M.; Bhowmick, S.; Saha, R.; Pandey, S.K.; Chakrabarti, S.ZnO is a fascinating large gap (3.37 eV) semiconductor, which exhibits intrinsically n-type conductive due to its native defects such as zinc interstitials and oxygen vacancies and such n-type related defects tend to compensate the p-type acceptor defects. However, the generation process of p-type defects is more challenging for developing a good quality homojunction optical device. Here we have studied the effect of ex-situ atmospheric annealing on conductivity of ZnO films. The ZnO films were deposited using RF sputtering on Si substrate temperature at 400°C substrate temperature and 2.2E-2 mbar gas pressure. The films were deposited in oxygen-rich ambient to achieve less oxygen vacancy defects in the film. The ex-situ atmospheric annealing is performed at higher temperature of 900 and 1000ºC. The effects of this post-deposition annealing on the electrical, structural, elemental and optical properties of ZnO thin films were investigated in detail. The X-ray Diffraction (XRD) results exhibited the hexagonal wurtzite structure (002) orientation. After annealing, the XRD peak is shifted at higher 2-thetha value, which indicates a reduction in lattice constant. Further, X-ray photoelectron spectroscopy (XPS) had been done and such XPS results confirmed that simultaneous generation of acceptor defects and reduction of oxygen vacancy related donor concentrations. The electrical properties of films were studied using hall measurement system. These electrical parameters were purposive to inspect the effect of ex-situ atmospheric annealing temperatures on conductivity of films. The Hall measurement confirmed that 1000ºC annealed films achieve p-type conductivity with high reproducibility and such p-type behavior exhibits high mobility. Thus, temperature induced conductivity reversal could be a potential and cost-effective technique to achieve highly stable p-type ZnO films. © 2023 SPIE.Item Facile hydrothermal synthesis of vanadium disulfide nanomaterial for supercapacitor application(SPIE, 2023) Mandal, A.; Pandey, N.; Pandey, S.K.; Yadav, A.K.; Chakrabarti, S.Vanadium disulfide (VS2) is a prominent metallic member of transition metal dichalcogenides (TMDs) family and has already demonstrated its flair in energy storage device applications such as supercapacitors and batteries. In this work, we have synthesized hexagonal shape VS2 nanomaterial using a facile one step hydrothermal route and investigated the phase, morphology and structural properties of the material. The formation of phase has been confirmed from the X-ray diffraction (XRD) plot by correlating with the database of Joint Committee on Powder Diffraction Standards (JCPDS) 00-036-1139 of 1T VS2. Further, the crystalline behavior of VS2 nanomaterial can be seen from the high resolution transmission electron microscopy (HRTEM) measurement. Moreover, the morphology of the synthesized material is obtained from the field emission gun-scanning electron microscopy (FEG-SEM). Also, the characteristic Raman peaks of 1T VS2 at 140.3 cm-1 and 192.3 cm-1 have been observed from the Raman spectrum indicating the metallic behavior of synthesized material. The peak at 281.8 cm-1 is attributed to the in-plane vibrational mode (E2g1) while the peak at 404.5 cm-1 represents the out-of-plane vibrational mode (A1g) of V-S bond. The Fourier transform infrared (FTIR) spectrum shows the V-S-V and V=S vibrational modes around 534 cm-1 and 982 cm-1 respectively. The study introduces a low cost, large scale, highly crystalline, and metallic VS2 nanomaterial with potential application for next generation supercapacitors and other energy storage devices. © 2023 SPIE.Item Synthesis of VS2/N-rGO nanocomposite material for energy storage application(SPIE, 2023) Mandal, A.; Pandey, S.K.; das Gupta, K.; Chakrabarti, S.Vanadium disulfide (VS2), which belongs to transition metal dichalcogenides (TMDs) group, is a prominent material for energy storage application. On the other hand, graphene like carbon-based nanomaterials offer improved electrochemical performance due to high specific surface area, excellent conductivity, good chemical, and mechanical stability. Therefore, composite of graphene like material with TMD have shown better electrochemical performance till date. In this work, we have synthesized VS2/N-rGO composite material, which can be applicable for energy storage device. At first, we have synthesized graphene oxide (GO) using Tour method. Then we reduced GO along with nitrogen doping using hydrothermal route. After that, we have synthesized VS2/N-rGO by hydrothermal method. The X-ray diffraction (XRD) spectrum of GO shows a prominent peak at 10.2°, which implies the interlayer spacing in GO of 8.7 Å. After reduction and doping with nitrogen (N), two peaks are obtained at 24.7° (d=3.6 Å), and 42.3° (d=2.1 Å) in the XRD pattern which corresponds to N-rGO. RAMAN spectrum of composite shows the characteristics peaks of VS2 at 141.6, 194.5, 286.4, 404.1, 680.1 and 997.2 cm-1 along with D and G bands coming from the N-rGO. We have also performed the Fourier-transform infrared-spectroscopy (FTIR) and Field-emission gun-scanning electron-microscopy (FEG-SEM) characterizations to investigate the bonding vibration and surface morphology of the materials. The synthesized material is suitable for energy storage applications. © 2023 SPIE.