Browsing by Author "Chakrabarti, S."

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Detection of acceptor-bound exciton peak at 300 K in boron–phosphorus co-doped ZnMgO thin films for room-temperature optoelectronics applications
(Elsevier B.V., 2021) Sushama, S.; Murkute, P.; Ghadi, H.; Pandey, S.K.; Chakrabarti, S.
It is well-known that the ZnMgO thin-film faces a roadblock in its potential applications for various optoelectronic devices due to the limitation imposed on achieving p-type conduction. The mono-acceptor doping of ZnMgO endures from the stern self-compensation by native donor defects and deep acceptor level formation advocating the need for alternate doping techniques like co-doping. In this paper, we report a detailed study on the improvement in structural, elemental, and optical properties of phosphorus-doped Zn0.85Mg0.15O thin films, with an aim to obtain enhancement in the signatures of acceptor-doped behavior, under the influence of boron implantation time. In addition, the paper also captures the behavior exhibited by the co-doped samples as a result of the variation in the annealing temperature. The solubility of the phosphorus atom (acceptor dopant) was observed to improve with boron (donor co-dopant) implantation as confirmed by the structural, elemental, and optical properties of co-doped ZnMgO thin films. It was also found that the acceptor level emissions got improved after boron implantation in phosphorus-doped ZnMgO thin films. Additionally, with co-doping, the sample showed the signature of acceptor-bound exciton peak till 300 K, evidencing the room-temperature operability of the films. Moreover, the fabricated film had a shallow acceptor energy level located at around 74 ± 0.45 meV above the valence band. Co-doped samples also showed stable acceptor based optical emission for more than a year. © 2020 Elsevier B.V.
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 600Â°C for four hours. The doped sample was annealed at temperature 700Â°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 34.173Â°, 34.624Â°, and 34.638Â° 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 âˆ¼134 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 (AXÂ°) peak around 3.588eV were found in photoluminescence spectra of sample B revels the phosphorus doping in ZnMgO. Â© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
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 800â„ƒ for 30 mins in Nitrogen (N2), and Oxygen (O2) ambient to achieve Î²-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 Î²-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. Â© 2022 SPIE.
Enhancement in structural, elemental and optical properties of boron–phosphorus Co-doped ZnO thin films by high-temperature annealing
(Elsevier B.V., 2021) Sushama, S.; Murkute, P.; Ghadi, H.; Pandey, S.K.; Chakrabarti, S.
The inherent n-type nature of zinc oxide (ZnO) and its unstable p-type behavior with single dopant species have encouraged researchers to explore the effect of multiple dopants as a viable solution for long-term stability and repeatability. Herein, we report boron (B) and phosphorus (P) co-doped ZnO thin films engineered through an optimized ion implantation technique followed by annealing at 1000 °C in oxygen ambiance. We investigated their structural, chemical, and optical properties to capture the effect of both boron implantation duration and annealing temperature. Co-doping with boron was observed to boost phosphorus incorporation in the film. Compared with P-doping, P–B co-doping increased the dominance of acceptor-bound exciton peak and also, suppressed non-radiative/visible emission which is due to reduced Madelung energy. After high-temperature annealing at 1000 °C, further narrowing of optical emission peaks generated due to acceptor incorporation was observed. Also, the co-doped samples showed stability in the acceptor behavior for more than one year. © 2021 Elsevier B.V.
Fabrication of 1T VS2 Electrode-Based In-Plane Micro-Supercapacitor Using a Cost-Effective Mask-Assisted Printing Technique
(John Wiley and Sons Inc, 2023) Mandal, A.; Yadav, A.K.; Pandey, S.K.; Chakrabarti, S.
Vanadium disulfide (VS2) is an important member of the transition-metal dichalcogenides (TMDs) family, which offers high conductivity. In nature, it can exist in two phases, i.e., 1T and 2H. Herein, the metallic 1T VS2-based in-plane micro-supercapacitor (MSC) is fabricated by a facile-mask-assisted printing technique. Initially, the 1T VS2 nanosheets are synthesized using a simple one-pot hydrothermal route. The material characterizations have claimed the formation of a 1T phase and the density of states (DOS) reveal that the 1T phase of VS2 is metallic in nature. After experimental and theoretical investigations of synthesized nanosheets, a VS2 electrode-based in-plane MSC is fabricated using a simple mask-assisted printing technique. The fabricated device demonstrates excellent capacitance retention of 97.6% after 1000 cycles of cyclic voltammetry measurement at a 100 mV s−1 scan rate. The device also shows an excellent areal capacitance of 212.7 mF cm−2 and a high areal energy density of 10.63 μWh cm−2 at a high-power density of 4.45 mW cm−2. This low-cost and simple fabrication process can produce high-performance in-plane MSC devices. © 2023 Wiley-VCH GmbH.
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. Â© 2023 SPIE.
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 600Â°C for 4 hrs. After in-situ annealing SOD process, sample has also been ex-situ annealed at 900Â°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. Â© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.
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. Â© 2021 SPIE.
Improvement in Performance of InAs Surface Quantum Dot Heterostructure-Based H2S Gas Sensor by Introducing Buried Quantum Dot Layer
(Institute of Electrical and Electronics Engineers Inc., 2023) Mantri, M.R.; Panda, D.P.; Punetha, D.; Pandey, S.K.; Singh, V.P.; Pandey, S.K.; Chakrabarti, S.
In this work, we have demonstrated InAs surface quantum dot (SQD)-based H2S gas sensors. The epitaxial growth of the strain-coupled and uncoupled InAs/GaAs QD heterostructures is done using the solid-source molecular beam epitaxy (MBE) tool. For both types of heterostructures, the coverage of the InAs monolayer (ML) for the SQD layer varies from 0.9 to 2 ML. The ML coverage of the buried quantum dots (BQDs) layer for the coupled heterostructures is kept constant (2.7 ML). The atomic force microscopy (AFM) results demonstrated that the coupled heterostructures have higher quantum dot (QD) density in the SQDs layer in comparison to the uncoupled one due to strain propagation from the BQDs toward the SQD layer. The sensor fabricated using the coupled heterostructure with 2 ML SQDs has demonstrated better performance than the uncoupled one for various concentrations (1-1000 ppm) of hydrogen sulfide (H 2S) gas due to inter-dot carrier tunneling between BQDs and SQDs layer. The coupled InAs gas sensor showed the best sensing properties at room temperature (45.9% sensor response at 100 ppm H2S ). We have demonstrated the selectivity of the sensor toward H 2S among various target gases like CO, CO2 , N2O , and NO 2 and the stability over a longer period of time with only 3% deviation (within acceptable limit). These findings have the potential to promote the fabrication of high-performance gas sensors using SQDs-based coupled heterostructures. © 2001-2012 IEEE.
Innovative structural engineering of sustainable and environment-friendly Cu2ZnSnS4 solar cell for over 20% conversion efficiency
(John Wiley and Sons Ltd, 2022) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.
Kesterite Cu2ZnSnS4(CZTS) thin-film technology has been comprehensively investigated over the last decade as a promising candidate in the field of photovoltaic technologies. However, despite numerous strategies to improve the performance, the efficiencies remain stagnant at around 11%. Poorly optimized absorber/buffer interface, non-absorption of higher wavelength photons, and non-ohmic back contact are the primary reasons for the poor performance of the CZTS solar cell. The authors of this paper propose a cadmium-free buffer layer, multiple quantum wells (MQWs) structure, and a back surface field (BSF) layer to overcome these issues, respectively. In this study, the buffer layer, zinc oxysulfide (Zn[O1−xSx]) is considered as an alternative to toxic Cadmium Sulfide (CdS) for better band alignment with the CZTS absorber layer. Cu2ZnSn(SxSe1−x)4 (CZTSSe) is used as a quantum well material in MQWs to increase photon absorption in CZTS solar cells. Tin selenide (SnSe) is used as the BSF layer to reduce the effect of non-ohmic back contact and to improve the open-circuit voltage (Voc) of MQW incorporated CZTS solar cells. Detailed analysis and optimization of the modified structure with higher performance are presented. The simulation results obtained provide imperative guidelines for the fabrication of high-efficiency CZTS solar cells using non-toxic and earth-abundant materials. © 2022 John Wiley & Sons Ltd.
Investigation of phosphorus-doping of MgZnO thin films using efficient spin-on dopant process
(Elsevier B.V., 2023) Mishra, M.; Saha, R.; Tyagi, L.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.
Phosphorus doped MgZnO thin films were prepared using the RF sputtering technique on a Si wafer, followed by spin-on doping (SOD) and annealing. The SOD is a cheap and non-destructive process in which the dopant film is spun on a Si wafer and placed in the vicinity of deposited undoped MgZnO thin film at a high temperature to perform doping. After doping, the MgZnO thin films were annealed at temperatures such as 700, 800, and 900°C, which significantly improved morphological, structural, and optical properties. The atomic force microscopy and scanning electron microscopy measurements revealed that phosphorus-doped MgZnO thin films annealed at 800–900°C have good morphology and large grains. X-ray diffraction spectra demonstrated the (002) orientation of MgZnO thin films. The photoluminescence spectra measured at 20 K demonstrated the acceptor bound exciton peak at 3.47 eV and acceptor binding energy of around 64.34 meV, indicating the formation of shallow acceptor levels by phosphorus doping of MgZnO thin films using the SOD process. In Raman spectroscopy measurement, the peak of E2high phonons mode of MgZnO wurtzite structure was observed around 436 cm−1. The FWHM value of this peak reduces with augmentation annealing temperature, demonstrating improvement in crystallinity. X-ray photoelectron spectroscopy measurement demonstrated the presence of phosphorus atoms in the SOD processed MgZnO thin films, which is again verified by Fourier-transform infrared spectroscopy measurement showing vibration modes of P–O bonds. It was observed that the different properties of SOD-prepared phosphorus-doped MgZnO films were superior to the film prepared using the alternate costly and destructive ion-implantation technique. These findings have revealed that high-quality phosphorus-doped p-type MgZnO thin films by the SOD process are very suitable for UV optoelectronic device applications. © 2023 Elsevier B.V.
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. Â© 2021 SPIE.
Phosphorus doping of ZnO using spin-on dopant process: A better choice than costly and destructive ion-implantation technique
(Elsevier B.V., 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.
Radio frequency sputtered ZnO thin films doped with phosphorus (ZnO:P) have been prepared employing spin-on dopant process. In the SOD process, the dopant film has been spin-coated on a silicon substrate and positioned close to the as-deposited undoped ZnO film at high temperature to perform the phosphorus doping. The high-resolution X-ray diffraction measurement reveals that the prepared ZnO:P films are good in crystalline quality which improves further by annealing. It is found that the full-width half-maximum corresponding to (002) peak of SOD processed thin films is much narrower than previously reported ion-implanted thin films, indicating the better crystalline quality of SOD processed phosphorus-doped ZnO thin films. The X-ray photoelectron spectroscopy measurement signifies that the P2O5 decomposes into two phosphorus atoms behaving like an acceptor dopant and five oxygen atoms which may fill in oxygen vacancies at high-temperature annealing. The photoluminescence spectra discover the acceptor bound exciton peak at 3.35 eV and free electron to acceptor level transitions at 3.31 eV. The calculated acceptor binding energy is 127 meV for the phosphorus dopant which works as a shallow acceptor level. It is found that the phosphorus-doped ZnO thin films prepared using the SOD process have much superior structural and optical properties in comparison to previously reported ion-implanted film. This study demonstrates that the SOD process is much superior than the ion-implantation process to produce high-quality ZnO:P thin films for very stable p-type conduction. © 2021 Elsevier B.V.
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 800Â°C, and phosphorus doped ZnO film by using spin-on dopant method at an elevated temperature of 800Â°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. Â© 2022 SPIE.
Room-temperature ultraviolet-ozone annealing of ZnO and ZnMgO nanorods to attain enhanced optical properties
(Springer, 2020) Alam, M.J.; Murkute, P.; Sushama, S.; Ghadi, H.; Mondal, S.; Paul, S.; Das, D.; Pandey, S.K.; Chakrabarti, S.
ZnO and ZnMgO nanorods have proven to be promising materials for sensing, UV and deep UV based optoelectronic applications. A major drawback of ZnO and ZnMgO based thin films and nanorods is the presence of native point defects which deteriorates their optical efficiency and becomes an impediment to their efficient device applications. The furnace and rapid thermal annealing processes have overcome this up to a great extent but being high temperature processes, they put many fabrication and technological limits in device fabrication. Especially keeping an eye on the future flexible devices, herein we report ultraviolet-ozone (UVO) annealing as a room-temperature, simple and cost-effective annealing method to improve the optical efficiency of ZnO and ZnMgO nanorods along with control of defect states. The ZnO and ZnMgO nanorods were grown by hydrothermal method and annealed in UVO irradiation. UVO annealing substantially improved near band emission and suppressed defect band emissions. It is found that zinc interstitial atoms migrate from the top portion of ZnO nanorods towards the bottom of nanorods after UVO annealing, resulting in reduced zinc interstitial defects in the top portion of nanorods. X-ray diffraction results showed improvement in structural properties. XPS results confirmed suppression of oxygen vacancies and zinc interstitials and improvement in lattice oxygen in the ZnO nanorods after UVO annealing. Optimum times of UVO annealing for ZnO and ZnMgO nanorods were 30 and 50 min respectively. These findings will be helpful for the further development of ZnO and ZnMgO nanorods based high performance optoelectronic devices and sensors. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.
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. Â© Â© 2022 SPIE.
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 10.2Â°, which implies the interlayer spacing in GO of 8.7 Ã…. After reduction and doping with nitrogen (N), two peaks are obtained at 24.7Â° (d=3.6 Ã…), and 42.3Â° (d=2.1 Ã…) 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. Â© 2023 SPIE.
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 400Â°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 1000ÂºC. 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 1000ÂºC 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. Â© 2023 SPIE.
Theoretical investigations of band alignments and SnSe BSF layer for low-cost, non-toxic, high-efficiency CZTSSe solar cell
(Elsevier Ltd, 2021) Prabhu, S.; Pandey, S.K.; Chakrabarti, S.
In this work, a numerical simulation approach is utilized using SCAPS-1D software to model, modify, optimize, and evaluate the CZTSSe solar cell structure. For the CZTSSe solar cell, one possible reason hindering the performance is improper band alignment between the absorber and the buffer layers. With conventional CdS as a buffer layer, having a fixed bandgap, tuning the band alignment is impossible. To overcome this issue, Cd-free zinc oxide-based compounds Zn(O1-xSx), Zn1-xSnxO, and Zn1-xMgxO are explored as buffer layers, and their performance is evaluated. Using their composition-dependent tunable bandgap as an advantage, suitable band alignment with the absorber layer is evaluated for equal or higher performance when compared to CdS. Further performance improvement is attempted by using SnSe as the back surface field (BSF) layer. Band alignment evaluation is also extended to the back contact (Mo)/SnSe interface, whereby an attempt is made to replace Mo with a suitable metal. The Ni is found as a good candidate to replace Mo to achieve high-efficiency solar cell. The same approach is repeated with the transparent conducting oxide layer, and aluminum doped zinc oxide (AZO) is found as a suitable material in place of ITO for optimized solar cell structure. A maximum power conversion efficiency of 17.55% is achieved with an optimized structure. It is also observed that the external quantum efficiency (EQE) of the solar cell is improved significantly in the blue photons region in comparison to the EQE of the champion solar cell. The optimized structure Ni/SnSe/CZT(S0.4Se0.6)/Zn(O0.3S0.7)/i-ZnO/AZO in this work will be very useful to fabricate low-cost and Cd-free high-efficiency kesterite solar cells. © 2021
Unfolding the conductivity reversal n- to p-type in phosphorus-doped ZnO thin films by spin-on dopant (SOD) process
(Institute of Physics, 2022) Mishra, M.; Saha, R.; Bhowmick, S.; Pandey, S.K.; Chakrabarti, S.
Phosphorus doping induced p-type doping in ZnO thin films based on spin-on dopant (SOD) process is reported in this article. Owing to the reduced dependence on the conventional amenities for diffusion/ion-implantation doping, the SOD process provides a simple and cheap doping method. The effect of SOD process temperature on conductivity ZnO thin films is investigated by altering the temperature from 700°C to 1000°C. Systematic field emission scanning electron microscopy analysis demonstrates the impact of doping temperature on the morphological properties of SOD. The x-ray diffraction measurements reveal that the p-type ZnO thin films had (002) preferred crystal orientation. At the same time, x-ray photoelectron spectroscopy validated the formation of the PZn-2VZn complex, which was responsible for the acceptor behaviour of films. Moreover, the photoluminescence spectra tracked down that the origin of 3.35 and 3.31 eV emission peaks is due to the acceptor bound exciton and free-electron to acceptor level transitions, respectively. Finally, an elevated hole concentration of 2.09 × 1016 cm-3 is achieved with a resistivity of 1.14 ω-cm at 800°C doping temperature. However, the film doped at 900°C and 1000°C showed n-type behaviour due to the generation of high concentration donor defects. Here, we successfully demonstrate that the SOD process has great potential to produce high-quality p-type ZnO thin films suitable for optoelectronic devices applications. © 2022 IOP Publishing Ltd.