Browsing by Author "Varadharajaperumal, S."

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A comprehensive study on effect of annealing on structural, morphological and optical properties of CdO and photodetection of heterojunction n-CdO/p-Si diode
(Elsevier GmbH, 2021) Poul Raj, I.L.P.; Chidhambaram, N.; Saravanakumar, S.; Sasikumar, S.; Varadharajaperumal, S.; Alagarasan, D.; Alshahrani, T.; Shkir, M.; AlFaify, S.
The present investigation reports the synthesis of CdO using the facile sol-gel technique. The CdO samples exhibit cubic structure and their crystalline quality increases with different sintering temperatures (550, 650, and 750 °C). The maximum entropy method (MEM) was applied to calculate the charge density distribution of the CdO samples and the two-dimensional charge density maps showed a slight enlargement in the cell volume of the CdO with sintering temperatures. The bandgap of the CdO samples varied from 2.89 to 2.66 eV with increasing sintering temperature. Heterojunction n-CdO/p-Si photodiodes were constructed (using CdO samples) on silicon wafers using the spin coating procedure. The ideality factor of the diodes is found to decrease from 5.2 to 4.2 with sintering temperatures of the CdO. The heterojunction diode constructed using the CdO sample sintered at 750 °C exhibited the highest responsivity and external quantum efficiency values of 0.34 A/W and 109 %, respectively. Improved crystallinity, responsivity, and quantum efficiency make the developed CdO device useful for optoelectronics. © 2021 Elsevier GmbH
Controlled growth of 1D-ZnO nanotubes using one-step hot plate technique for CZTS heterojunction solar cells
(2020) Varadharajaperumal, S.; Alagarasan, D.; Ganesan, R.; Satyanarayan, M.N.; Hegde, G.
Present work reports a simple, rapid, one-step hot plate technique for systematic growth transformation of highly oriented ZnO nanorods (ZNRs) into ZnO nanotubes (ZNTs). The controlled growth of ZnO nanostructures (nanorods and nanotubes) was achieved at low temperature (90 C) in a short time (1hr) in a sealed weighing bottle (100 ml). It is observed that as the Zinc precursor concentration increases, a vertically grown ZnR morphology evolves into ZNT. The crystal structure of as-grown ZnO nanostructures, surface morphology, phase, and optical energy gap were respectively characterized by XRD, FESEM, Raman, XPS, CL and UV Vis spectroscopy. Grown nanostructures are further explored for their application in CZTS based heterojunction photovoltaics. 2019
Controlled growth of 1D-ZnO nanotubes using one-step hot plate technique for CZTS heterojunction solar cells
(Elsevier Ltd, 2020) Varadharajaperumal, S.; Alagarasan, D.; Ganesan, R.; Satyanarayan, M.N.; Hegde, G.
Present work reports a simple, rapid, one-step hot plate technique for systematic growth transformation of highly oriented ZnO nanorods (ZNRs) into ZnO nanotubes (ZNTs). The controlled growth of ZnO nanostructures (nanorods and nanotubes) was achieved at low temperature (90 °C) in a short time (1hr) in a sealed weighing bottle (100 ml). It is observed that as the Zinc precursor concentration increases, a vertically grown ZnR morphology evolves into ZNT. The crystal structure of as-grown ZnO nanostructures, surface morphology, phase, and optical energy gap were respectively characterized by XRD, FESEM, Raman, XPS, CL and UV–Vis spectroscopy. Grown nanostructures are further explored for their application in CZTS based heterojunction photovoltaics. © 2019
Effect of CuPc and PEDOT:PSS as hole transport layers in planar heterojunction CdS/CdTe solar cell
(2019) Varadharajaperumal, S.; Ilango, M.S.; Hegde, G.; Satyanarayan, M.N.
This paper presents the fabrication and photovoltaic performance of new architecture based planar heterojunction CdS/CdTe thin film solar cells which were employed with two hole transport layers (PEDOT:PSS as HTL1 and CuPc as HTL2). The reported solar cells were fabricated through various deposition techniques such as sputtering, thermal evaporation, spin coating and characterized by FESEM, AFM, XPS, UPS and AM 1.5 solar simulator. The interfacial layer growth and chemical state identification of the deposited thin films were studied by cross-sectional FESEM and XPS techniques. The band bending occurs between absorbing and transporting layer helps to inject the excited charge carriers effectively into electrode that was explained using UPS analysis. The present work intends to explain the role of additional window layer (TiO2), buffer layer (CdS) and hole transporting layers (PEDOT:PSS and CuPc) in the novel device architecture. Further, these findings will offer new research directions to address the double hole transport (back contact) layers selection concept in CdS/CdTe heterojunction based solar cells. 2019 IOP Publishing Ltd.
Effect of CuPc and PEDOT:PSS as hole transport layers in planar heterojunction CdS/CdTe solar cell
(Institute of Physics Publishing helen.craven@iop.org, 2019) Varadharajaperumal, S.; Ilango, M.S.; Hegde, G.; Satyanarayan, M.N.
This paper presents the fabrication and photovoltaic performance of new architecture based planar heterojunction CdS/CdTe thin film solar cells which were employed with two hole transport layers (PEDOT:PSS as HTL1 and CuPc as HTL2). The reported solar cells were fabricated through various deposition techniques such as sputtering, thermal evaporation, spin coating and characterized by FESEM, AFM, XPS, UPS and AM 1.5 solar simulator. The interfacial layer growth and chemical state identification of the deposited thin films were studied by cross-sectional FESEM and XPS techniques. The band bending occurs between absorbing and transporting layer helps to inject the excited charge carriers effectively into electrode that was explained using UPS analysis. The present work intends to explain the role of additional window layer (TiO2), buffer layer (CdS) and hole transporting layers (PEDOT:PSS and CuPc) in the novel device architecture. Further, these findings will offer new research directions to address the double hole transport (back contact) layers selection concept in CdS/CdTe heterojunction based solar cells. © 2019 IOP Publishing Ltd.
Enriched optoelectronic properties of cobalt-doped ZnO thin films for photodetector applications
(Springer, 2021) Vinoth, S.; Arulanantham, A.M.S.; Saravanakumar, S.; Rimal Isaac, R.S.; Soundaram, N.; Chidhambaram, N.; Alagarasan, D.; Varadharajaperumal, S.; Shkir, M.; AlFaify, S.
Cobalt-doped ZnO (ZnO:Co) thin films were synthesized using the chemical bath deposition technique for their potential application in ultraviolet (UV) photosensing. All the prepared samples were characterized using XRD, FESEM, EDX, PL, XPS, and UV–Vis absorption techniques. The UV photosensing property of the thin films was examined under the illumination of UV light (365 nm). The structural and morphological investigations reveal that the ZnO:Co samples have a hexagonal wurtzite crystal structure with nanowire morphology. An increase in crystallite size and a decrease in the bandgap of the samples were observed owing to the replacement of the Co2+ ions in the regular sites of Zn2+. The PL spectra show some defect emission peaks in the visible region because of the occurrence of oxygen vacancies, which suggests a high photoabsorption property of the samples. The XPS study was performed to understand the existence of elements and their binding states in the fabricated thin films. The UV photosensing studies reveal that the highest responsivity of 0.918 AW?1 was achieved for the ZnO:Co (1%) sample. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Morphology controlled n-type TiO2 and stoichiometry adjusted p-type Cu2ZnSnS4 thin films for photovoltaic applications
(2017) Varadharajaperumal, S.; Sripan, C.; Ganesan, R.; Hegde, G.; Satyanarayan, M.N.
This paper presents the fabrication and characterization of stoichiometry adjusted Cu2Zn1.5Sn1.2S4.4 thin film (FTO/TiO2/CdS/CZTS/Au) photovoltaic (PV) devices. The PV devices were developed using the window layer of rutile TiO2 nanoarchitecture arrays, i.e., one-dimensional (1D) nanorods and three-dimensional (3D) combined/ hierarchical structures (nanorods with microspheres). Onedimensional (1D) nanorods and 3D combined structures of TiO2 window layers were synthesized by a hydrothermal method with different solvents without any assistance of surfactants and templates. We achieved two kinds of TiO2 nanostructures by tuning the precursor concentrations and volume by keeping a constant growth time and temperature. The detailed structural properties were studied using X-ray diffraction and high resolution transmission electron microscopy. Phase formation and chemical state of the prepared samples were examined by Raman spectroscopy and X-ray photoelectron spectroscopy. The surface morphology and luminescence studies of TiO2 nanostructures were analyzed using field emission scanning electron microscopy and cathodoluminescence techniques. The current-voltage performance of fabricated devices were measured under an AM 1.5 solar simulator. It is observed that combined structure PV device shows better efficiency (1.45%) than the nanorods alone structure (0.55%). Present work is a first attempt made to construct the inverted CZTS based solar cells. This study establishes the window layer of hierarchical TiO2 nanostructures based morphology that offers a great potential for the development of high-efficiency nonstoichiometric CZTS based solar cells. 2017 American Chemical Society.
Morphology controlled n-type TiO2 and stoichiometry adjusted p-type Cu2ZnSnS4 thin films for photovoltaic applications
(American Chemical Society, 2017) Varadharajaperumal, S.; Sripan, C.; Ganesan, R.; Hegde, G.; Satyanarayana, M.N.
This paper presents the fabrication and characterization of stoichiometry adjusted Cu2Zn1.5Sn1.2S4.4 thin film (FTO/TiO2/CdS/CZTS/Au) photovoltaic (PV) devices. The PV devices were developed using the window layer of rutile TiO2 nanoarchitecture arrays, i.e., one-dimensional (1D) nanorods and three-dimensional (3D) combined/ hierarchical structures (nanorods with microspheres). Onedimensional (1D) nanorods and 3D combined structures of TiO2 window layers were synthesized by a hydrothermal method with different solvents without any assistance of surfactants and templates. We achieved two kinds of TiO2 nanostructures by tuning the precursor concentrations and volume by keeping a constant growth time and temperature. The detailed structural properties were studied using X-ray diffraction and high resolution transmission electron microscopy. Phase formation and chemical state of the prepared samples were examined by Raman spectroscopy and X-ray photoelectron spectroscopy. The surface morphology and luminescence studies of TiO2 nanostructures were analyzed using field emission scanning electron microscopy and cathodoluminescence techniques. The current-voltage performance of fabricated devices were measured under an AM 1.5 solar simulator. It is observed that combined structure PV device shows better efficiency (1.45%) than the nanorods alone structure (0.55%). Present work is a first attempt made to construct the inverted CZTS based solar cells. This study establishes the window layer of hierarchical TiO2 nanostructures based morphology that offers a great potential for the development of high-efficiency nonstoichiometric CZTS based solar cells. © 2017 American Chemical Society.
Toxic-free surface level sulphur doped 1D Ti-Ox-Sy nanorods for superstrate heterojunction CZTS thin-film solar cells
(Elsevier Ltd, 2021) Varadharajaperumal, S.; Alagarasan, D.; Sripan, C.; Ganesan, R.; Satyanarayan, M.N.; Hegde, G.
Surface level sulphur (S) doped TiO2 nanorods (S-TNRs) were fabricated via toxic-free novel three-step processes such as low-temperature hydrothermal method followed by thermal evaporation (S layer) and post-annealing (350 °C, 450 °C and 550 °C) techniques. Present work focuses on the comprehensive studies of surface level doping, structure, morphology and compositional properties of different temperature annealed S-TNRs for CZTS thin-film (Au/CZTS/S-TNRs/TNRs/FTO) solar cells. The oxidation states of incorporated S atoms in the TiO2 matrix were identified from X-ray photoelector spectroscopy (XPS) analysis. A reduction in bandgap for 350 °C annealed S-TNRs film was observed from UV-Vis spectroscopy. The electrical characteristics showed the fabricated solar cells strongly depend on the S-TNRs annealing temperature. Proposed technique would be useful in effective and controlled (surface level) doping of S atoms into any desired nanostructured metal oxides for optoelectronic applications and, further useful in fabricating cadmium (Cd) free buffer layer in chalcogenide solar cells. © 2020 Elsevier Ltd