Centre for Nanosciences
Amrita Institute of Medical Sciences,
Amrita Vishwa Vidyapeetham
AIMS Ponekkara P. O., Kochi, Kerala - 682 041, India.

0484 285 8750
researchsecretary@aims.amrita.edu
 

 

Dr. Mariyappan joined as an Assistant Professor at Amrita Center for Nanosciences and Molecular Medicine in June 2016. He obtained his PhD from South Dakota State University, USA in 2011. He has developed advanced gas-phase surface passivation schemes for nanostructured electron acceptors using atomic layer deposition at The Minnesota Nano Center, University of Minnesota. He was a postdoctoral researcher at the College of Nanoscale Science and Engineering, State University of New York, USA, during 2011-2014 and then worked in Worcester Polytechnic Institute for a year. In 2015, he established a research and development division in a Silicon Valley-based startup company, Macromolecular Inc., to develop photovoltaic materials and devices for space PV applications.  

He has published over 20 journal papers including in Nanoscale, ACS Nano and Nano Energy, 20 peer-reviewed conference proceeding papers (IEEE and MRS) and a book chapter. He has been serving as an invited reviewer for 10 journals including ACS Applied Materials & Interfaces, Journal of Applied Physics, Solid State Electronics and AIP Advances.  

Dr. Mariyappan’s research explored various issues in semiconductor materials and devices. His major research areas are defect passivation in semiconductors, device fabrication/characterization, studies on charge transport, bulk and interfacial recombination. His current research includes developing energy harvesting technologies and other opto-electronic devices using emerging nanostructured materials.

Extra Mural Research Funding: "Transformative Approaches for Design and Development of 2-D Carbon Photovoltaics" Awarded by Science and Engineering Research Board (SERB)-2018, Status: Principal Investigator.

Early Career Award: "Chemical Vapor Deposition Assembled 2D Layered Semiconductors Enabled Electrochemical Solar Cells" Science and Engineering Research Board (SERB)-2018.Status: Principal Investigator.

Publications

Publication Type: Journal Article

Year of Publication Title

2021

N. Suresh Powar, Ramanathan, K. Velu, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Structural, nanomorphological and optical characteristics of self-assembled 2D-layered WS2-CdTe quantum dot heterostructure”, Materials Letters, vol. 285, p. 129139, 2021.[Abstract]


Self-assembled heterostructure of 2D-layered tungsten disulfide (WS2) with Cadmium telluride (CdTe) quantum dots is reported. CdTe quantum dots (8 nm–10 nm) were intercalated into 2D-layered WS2 which showed an approximate lateral length distribution of 1 µm. X-ray photoelectron spectroscopic studies confirmed Cd (3d5/2, 3d3/2), Te (3d5/2, 3d3/2), W (4f7/2, 4f5/2) and S (2p3/2, 2p1/2) in the WS2-CdTe heterostructure which exhibited an optical absorption in the spectral range of 200 nm–550 nm. The dominant optical absorption around 250 nm is attributed to the quantum size effects occurred on both WS2 and CdTe. A sharp photoluminescence emission at 600 nm was further observed to be tunable with respect to concentration of CdTe quantum dots into the WS2 layers.

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2021

D. Krishnan, Powar, N. Suresh, Vasanth, A., Ramanathan, K. Velu, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Graphene oxide enabled hole transport characteristics in iodide/tri-iodide for improved dye sensitized solar cell performance”, Materials Letters, vol. 285, p. 129176, 2021.[Abstract]


Adding 6 wt% of graphene oxide (GO) into iodide-triiodide (I−/I−3) electrolyte improved dye sensitized solar cell (DSSC) performance by a factor of 100% (from 3.5% to 7.0%) by achieving effective hole transport. Performance of DSSCs was suppressed by a factor of 17% (from 3.5% to 2.9%) due to the GO more than 6 wt%. GO improved the hole transport for an optimum concentration in the I−/I−3 while impeded the same for higher concentration due to the reduction in diffusivity. The presented work established a simple and straight forward approach to improve the performance of DSSCs by improving hole transport.

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2020

G. Gopakumar, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Assessing the role of plasma-engineered acceptor-like intra- and inter-grain boundaries of heterogeneous WS2–WO3 nanosheets for photocurrent characteristics”, Nanoscale Adv., vol. 2, pp. 2276-2283, 2020.[Abstract]


High-temperature annealing in tungsten disulfide resulted in heterogeneous WS2–WO3 in which intra- (within WS2 and WO3) and inter- (between WS2 and WO3) grain boundaries were observed, which were highly critical for charge transport and recombination. The heterogeneous WS2–WO3 phase was evidenced by observing the coexistence of d-spacing values of 0.26 nm (WS2) and 0.37 nm (WO3) in transmission electron microscopic (TEM) studies. Further systematic high-resolution TEM studies elucidated that intra-grain boundaries separated crystallites within WS2 and WO3, while inter-grain boundaries separated WS2 from WO3. As WS2 and WO3 are both n-type, these defects are acceptor-like in the grain boundaries and they actively participate in the capture (trapping) process, which impedes charge transport characteristics in the heterogeneous WS2–WO3 films. Plasma treatment in the heterogeneous WS2–WO3 film, for 60 minutes using argon, energetically modulated the defects in the intra/inter-grain boundaries, as evidenced from detailed comparative photocurrent characteristics obtained individually in (i) pristine WS2, (ii) heterogeneous WS2–WO3 and (iii) Ar plasma-treated heterogeneous WS2–WO3 films under blue and green lasers, along with AM1.5 (1 sun) illumination. Detrimental roles (trapping/de-trapping and scattering) of grain boundary states on photoelectrons were seen to be significantly suppressed under the influence of plasma.

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2020

P. Mani, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Thickness-dependent hole-blocking capability of RF-sputtered nickel oxide compact layers in dye-sensitized solar cells”, vol. 3, no. 2, pp. 117 - 124, 2020.[Abstract]


Photo-generated charge carrier recombination in dye-sensitized solar cells (DSSCs) is observed to be suppressed significantly at the interface between transparent fluorine-doped tin oxide (FTO) and titanium dioxide (TiO2) by coating nickel oxide (NiO) thin film by RF sputtering. UV-Visible optical absorption spectroscopic measurements performed in the wavelength window of 300–800 nm showed ~ 60% average transmittance for NiO thin films coated for 10 min. The calculated optical bandgap value for NiO was 3.4 eV. The RF-sputtered NiO films were thoroughly characterized by X-ray photo-electron spectroscopy to examine Ni 2p3/2 and Ni 2p1/2 along with O 1s. The present study assessed the effect of 5, 10, and 15 min RF-sputtered NiO thin films at the interface between FTO and mesoporous TiO2. Results showed that charge transport in DSSCs is highly sensitive to NiO thickness at the interface between FTO and TiO2. It was specifically noticed that 10 min coating of NiO on FTO yielded DSSCs with photo-conversion efficiency (η) of ~ 6.8% while DSSCs with no NiO on FTO showed only 4.9%. Further increase in NiO thickness affected the performance of DSSCs due to the significant reduction in tunneling probability from TiO2 to FTO.

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2020

A. Vasanth, Powar, N. Suresh, Krishnan, D., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Electrophoretic graphene oxide surface passivation on titanium dioxide for dye sensitized solar cell application”, Journal of Science: Advanced Materials and Devices, vol. 5, pp. 316-321, 2020.[Abstract]


A dominant interfacial recombination pathway in the dye sensitized solar cell (DSSC) was suppressed by coating graphene oxide (GO) on the titanium dioxide (TiO2) nanoparticle layer via the electrophoretic deposition (EPD) method. DSSC utilizing 5 min coating of GO by EPD on TiO2 nanoparticle layer showed 5% enhancement in the photo-conversion efficiency (from 5.7% to 6.0%), and 5% enhancement in the short circuit current density (from 11.4 mA/cm2 to 12.0 mA/cm2) in comparison with reference DSSCs which did not use GO on TiO2. GO coating on TiO2 is attributed to the efficient suppression of the photo-generated electron–hole recombination at the TiO2/dye/electrolyte interfaces. The further increase in the thickness of GO (10- and 20-min EPD coating) on the TiO2 nanoparticle layer impeded the charge transport as the performance of the respective DSSCs was significantly affected. It suggested that the probability of photo-generated electron tunneling from dye to TiO2 was suppressed by increasing the thickness of the GO layer. Presented results assure that GO can be considered as a competitive surface passivation candidate for nanostructured excitonic solar cells.

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2020

K. Velu Ramanathan, Shankar, B., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Grain/grain-boundary mediated dispersive photo-current characteristics in close space sublimated micro-granular CdTe films”, IET Optoelectronics, vol. 14, pp. 252-255, 2020.[Abstract]


Photo-current characteristics in close space sublimation processed multi-facetted Cadmium Telluride (CdTe) micro-granular films were studied under AM1.5, blue and green laser illuminations to assess the energy dependent charge transport characteristics. Photo-current under AM1.5 illumination (100 mW/cm2) resulted in three times more than dark current while it was observed 2.4 and 2.5 times more in case of blue and green laser illuminations, respectively. While all the three illuminations (AM1.5, blue and green lasers) were capable to generate photo-electrons in CdTe, the variation in magnitude was articulated to the effect of grain boundaries present across the charge transport pathways as evidenced from the surface morphology examined by scanning electron microscopic studies which asserted that CdTe films were micro-granular in nature separated by grain boundaries. It is elucidated in the measurements that charge carriers under the illumination of AM1.5 light, acquired energy to overcome the grain boundaries easily compared to the charge carriers produced by blue and green light sources as evidenced from the photo-current measurements.

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2020

L. Srinivasan, Ramanathan, K. Velu, Gopakumar, G., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “RF-sputtered tungsten enabled surface plasmon effect in dye sensitised solar cells”, IET Optoelectronics, vol. 14, pp. 274-277, 2020.[Abstract]


This work examined the possibility of overcoming narrow band optical absorption of organic dyes in the range of 350–700nm via surface plasmon effect mediated by RF-sputtered tungsten (W) thin film on mesoporous TiO2 for dye-sensitised solar cells (DSSCs) application. The UV–visible spectroscopic measurement showed optical absorption of W-film in the spectral range of 350–700nm with a dominant characteristic feature in the range of 350–550nm. W-thin film-coated TiO2 was used as an electron acceptor in DSSCs and observed ∼28% enhancement in short circuit current density compared to that of in a pristine TiO2-based DSSC which did not use W-thin film on TiO2. It is attributed to the local field-induced enhancement in optical absorption which resulted in improved exciton generation and effective charge transport in DSSCs enabled by W-thin film coating onto mesoporous TiO2.

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2020

K. Velu Ramanathan, Shankar, B., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Effects of gas-phase and wet-chemical surface treatments on substrates induced vertical, valley–hill & micro-granular growth morphologies of close space sublimated CdTe films”, Nanoscale Adv., vol. 2, pp. 4757-4769, 2020.[Abstract]


We implemented gas-phase (argon plasma) and wet-chemical (HNO3) surface treatments on close space sublimated (CSS) Cadmium Telluride (CdTe) thin films exhibiting morphologies of (i) vertically aligned walls on copper (Cu) and stainless steel (SS) substrates, (ii) valley–hills on aluminum (Al) substrates and (iii) micro-granules on nickel (Ni). As all the growth conditions (temperature, pressure, duration and source/substrate distance) were exactly the same in the CSS process to coat CdTe films, it is asserted that the various microstructures were raised only on Cu, Al, Ni and SS substrates. Plasma and HNO3 surface treatments on metal substrates did not affect the CdTe morphologies in terms of specific structures but it was observed that structural, optical and electrical charge transport characteristics were highly tunable by the two surface treatments. Thus, substrate driven morphological evaluation followed by surface treatments was enabled. The present study demonstrated various microstructures of CdTe films on metallic thin foil substrates to attempt the establishment of flexible opto-electronics based on CdTe.

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2020

A. Vasanth, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Post-annealing effect on the structural and optical properties of electrophoretically coated 2D-Layered MoSe2”, Journal of Science: Advanced Materials and Devices, 2020.[Abstract]


Temperature dependent changes in the structural, nanomorphological and optical characteristics of the 2D layered molybdenum diselenide (MoSe2), processed by electrophoretic coating (EPC) method, were examined. EPC processed MoSe2 was subjected to Raman spectroscopy confirming distinct active modes of A1g, E11g and E22u at 240.9 cm−1, 282.53 cm−1 and 337.7 cm−1, respectively. The in- and out-of plane vibrational modes observed in the Raman spectra were asserted as the 2H–MoSe2 phase which was not affected by the post annealing temperature. X-ray photoelectron spectroscopic measurements confirmed the states of Mo 3d at 228.9 eV and 232.1 eV, and of Se 3d at 54.5 eV and 55.3 eV. Studies on the surface morphology of the EPC processed MoSe2 showed significant changes due to the post-annealing treatment performed at 150 °C, 250 °C and 350 °C in terms of morphology, flake-size distribution and compactness of the film. The samples annealed at 150 °C and 250 °C showed a better optical absorption in the visible and the near infrared spectral regions with dominant characteristic peaks at 691.2 nm and 801.6 nm. Further studies assured that the EPC process yielded good quality and large area MoSe2 films with exotic structural, optical and nanomorphological characteristics that are highly suitable for functional devices.

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2020

G. Gopakumar, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Plasma Driven Nano-morphological Changes and Photovoltaic Performance in dye Sensitized 2D-layered Dual Oxy-sulfide Phase WS2 Films”, Nanoscale, vol. 12, no. 1, pp. 239-247, 2020.[Abstract]


The present work examined dye sensitized 2D layered tungsten disulfide (WS2) as a photo-anode in solar cells with no use of nanocrystalline metal oxides as electron acceptors such as titanium dioxide. It is observed that coating WS2 directly onto a fluorine doped tin oxide (FTO) transparent conductor, annealed at 530 °C, resulted in a mixed oxy-sulfide dual phase as confirmed by transmission electron microscopy and X-ray diffraction studies. Further studies on the surface morphology of the dual phase WS2–WO3 film showed a random distribution of platelets which further shaped into precisely regulated hexagonal platelets upon plasma treatment. High resolution transmission electron microscopic studies elucidated two different phases, WS2 and WO3, with d-spacing values of 0.26 nm and 0.37 nm, respectively. A well-defined grain boundary was also observed which separated the oxy-sulfide phase in the sample. The dual WS2–WO3 phase films showed optical absorption in the wavelength range of 350 nm–800 nm with a systematic increase in plasma exposure duration. Photovoltaic devices fabricated using the WS2–WO3 mixed phase photo-anodes resulted in 0.61% efficiency (η) which further was observed to be sensitive to the plasma exposure as it was observed that the 20 minute plasma treated sample increased the η value to 0.67%. Plasma treatment on the dual-phase samples orients and modifies the shapes of the platelets with a significant change in the surface which eventually influences the charge transport in resulting photovoltaic devices and thus the variation with respect to exposure duration.

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2020

N. S. Powar, Gopakumar, G., Ramanathan, K. V., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Chemical Bath Deposited WS2 Quantum Dots on TiO2 for Dye Sensitized Solar Cell Applications ”, Optical and Quantum Electronics, vol. 52, no. 2, p. 65, 2020.[Abstract]


Tungsten disulphide (WS2) quantum dots, coated on titanium dioxide (TiO2) by chemical bath deposition, increased the photovoltaic performance of dye sensitized solar cells (DSSCs) by ~ 11%. WS2 quantum dots exhibited a dominant optical absorption in a spectral range of 350–800 nm with its characteristics peaks at 550 nm and 620 nm corresponding to the direct bandgap optical transition at the K-point. X-ray photoelectron spectroscopic measurement was performed to study W 4f and S 2p peaks assured the presence of phase-pure WS2 quantum dots. Further, transmission electron microscopic studies showed a distribution of 8.5–20 nm quantum dots with d-spacing of 0.33 nm confirming the WS2. Photovoltaic characteristics of DSSCs with WS2 quantum dots asserted the additional photo-electrons generated by WS2 via the increment in photocurrent density and overall performance. This study demonstrated the possibility of integrating 2D-layered quantum dots into DSSCs as an additional photo-absorbing material candidate along with organic photo-sensitizer such as Ruthenium based N719.

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2020

A. Vasanth, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Microwave Engineered Structural, Nano-morphological and Photo-responsive Characteristics in 2D-layered Dual-phase MoO3-MoSe2 Films”, Applied Surface Science, vol. 519, p. 146263, 2020.[Abstract]


Microwave treatment in 2D-layered molybdenum diselenide (MoSe2) nanoflakes effectively changed structural, optical and charge transport characteristics at the nanoscale level due to the formation of MoO3-MoSe2 dual-phase. The co-existing MoO3-MoSe2 dual-phase, enabled by microwave treatment in pristine MoSe2, was highly sensitive to microwave thermal energy which caused significant shifts in Raman characteristic peaks due to the formation of dual phase which further confirmed in X-ray diffraction. It was also asserted by X-ray photoelectron spectroscopic studies which showed the effects of microwave induced changes on surface chemical characteristics of pristine MoSe2. Specifically, the loosely packed van der Waals sheet-like layers in pristine MoSe2 were engineered by microwave treatment and resulted in platelet-like nanostructures as evidenced in scanning electron microscopic studies. Further, charge transport characteristics in MoSe2 films were examined under dark, AM1.5, blue and green laser illuminations. Microwave treated MoSe2 showed a greater enhancement in photo-response than pristine MoSe2 due to the co-existing MoO3-MoSe2 dual-phase. Thus, microwave treatment can be considered for the development of 2D-optoelectronics as a feasible method to tune the physical properties according to requirements.

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2019

G. Gopakumar, Ashok, A., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Atomically Thin 2D Layered MoS2-enabled Photo-Current Characteristics in TiO2 Nanoparticle Films”, Applied Nanoscience (In Press), 2019.[Abstract]


The present study examines photo-current characteristics of 2D layered molybdenum disulfide (MoS2) incorporated titanium dioxide (TiO2) nanoparticle films at different illumination conditions established using while light (AM1.5), blue (406 nm), and green (525 nm) lasers. Photo-current values, measured from a two-terminal device configuration fabricated using TiO2 nanoparticle films with different weight % of MoS2, were observed to be sensitive to the quantity of MoS2 in the bulk TiO2. It is observed that incorporation of 30 wt% of MoS2 in TiO2 enhanced photo-current up to 48.3% compared to that of pristine TiO2 nanoparticle film under AM1.5 illumination. Blue and green laser-based measurements show that the photo-current is highly sensitive to the weight fraction of MoS2 in TiO2 and incident energy used to generate excitons. The variation observed in the measured photo-current is directly attributed to the optical responsivity of MoS2 to the incoming photons

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2019

A. Ashok, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Spray Pyrolysis-Coated Nano-Clustered CdTe on Amorphous Si Thin Films for Heterojunction Solar Cells”, Applied Nanoscience (Switzerland) (In Press), 2019.[Abstract]


Heterojunction solar cells are demonstrated employing spray pyrolysis-processed nano-clustered cadmium telluride (CdTe) on DC-sputtered amorphous silicon (a-Si) as p- and n-type layers, respectively. CdTe and a-Si films were subjected to X-ray photoelectron spectroscopic measurements showing Cd 3d (404.9 eV) and Te 3d (575.8 eV) peaks corresponding to CdTe while the peaks Si 2p (98.3 eV) and Si 2 s (148.3 eV) represent a-Si. Heterojunction solar cells with a stacked structure of FTO/a-Si/CdTe/Al resulted in a photo-conversion efficiency of 2.7% for an optimized thickness values of a-Si (1 µm) and CdTe (6 µm) films. © 2019, King Abdulaziz City for Science and Technology.

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2018

S. H, Dr. Mariyappan Shanmugam, M, M., and J.H., M., “Review on Dye-sensitized Solar Cells based on Polymer Electrolytes”, International Journal of Engineering and Technology(UAE), 2018.

2018

S. N. Vijayaraghavan, Ashok, A., Gopakumar, G., Menon, H., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “All Spray Pyrolysis-coated CdTe–TiO2 Heterogeneous Films for Photo-Electrochemical Solar Cells”, Materials for Renewable and Sustainable Energy, vol. 7, p. 12, 2018.[Abstract]


Cadmium telluride (CdTe) thin films of different thicknesses deposited onto titanium dioxide (TiO2) nanoparticle layer by spray pyrolysis deposition (SPD) are demonstrated as major photo-active semiconductor in photo-electrochemical solar cell configuration using iodide/triiodide (I−/I3−) redox couple as a hole transport layer. The CdTe–TiO2 heterogeneous films were characterized by X-ray photoelectron spectroscopy which identified doublet split of Cd 3d and Ti 2p which confirms CdTe and TiO2. Optical absorbance and transmittance of CdTe and TiO2 films which were examined by UV–Vis spectroscopy confirm that the optical bandgap of CdTe is 1.5 eV with a dominant photo-absorption in the spectral window of 350–800 nm, while TiO2 showed a bandgap of 3.1 eV and is optically transparent in the visible spectral window. The present work examined photo-anodes comprising 1, 3, 5, and 10 SPD cycles of CdTe coated on TiO2 nanoparticle layer. The solar cell with 5 SPD cycles of CdTe resulting in 0.4{%} efficiency. Results can be articulated to the CdTe deposited by 5 SPD cycles provided an optimum surface coverage in the bulk of TiO2, while the higher SPD cycles leads to agglomeration which blocks the porosity of the heterogeneous films.

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2018

G. Gopakumar, Menon, H., Ashok, A., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Two Dimensional Layered Electron Transport Bridges in Mesoscopic TiO2 for Dye Sensitized Solar Cell Applications”, Electrochimica Acta, vol. 267, pp. 63 - 70, 2018.[Abstract]


The present work demonstrates the possibility of facilitating electron transport in mesoscopic titanium dioxide (TiO2) by incorporating nanoflakes of layered molybdenum disulfide (MoS2) as an alternate electron transport bridge. Results suggest that performance of dye sensitized solar cells (DSSCs) can be increased up to ∼16% (from 7.39% to 8.55%) by incorporating 0.2 wt % of MoS2 into the bulk of TiO2, due to the significant improvement in electron lifetime from 8 ms to 23 ms. The nanoflakes of MoS2 form alternate electron transport bridges in the bulk TiO2 nanoparticle film through which photo-injected electrons travel more efficiently to reach transparent electrode compared to DSSCs utilize only TiO2 without MoS2. Presence of atomically thin layered MoS2 nanoflakes in the bulk of TiO2 assist the photo-electrons to skip electron-hole capture processes occur through TiO2 surface states to avoid the interfacial recombination. Further increment in the concentration of MoS2 suppresses the resulting DSSC performance by blocking the porosity which results in less dye adsorption and hence lower photocurrent values

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2018

A. Ashok, Vijayaraghavan, S. N., Unni, G. E., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “On the Physics of Dispersive Electron Transport Characteristics in SnO 2 Nanoparticle-based Dye Sensitized Solar Cells”, Nanotechnology, vol. 29, p. 175401, 2018.[Abstract]


The present study elucidates dispersive electron transport mediated by surface states in tin oxide (SnO 2 ) nanoparticle-based dye sensitized solar cells (DSSCs). Transmission electron microscopic studies on SnO 2 show a distribution of ∼10 nm particles exhibiting (111) crystal planes with inter-planar spacing of 0.28 nm. The dispersive transport, experienced by photo-generated charge carriers in the bulk of SnO 2 , is observed to be imposed by trapping and de-trapping processes via SnO 2 surface states present close to the band edge. The DSSC exhibits 50% difference in performance observed between the forward (4%) and reverse (6%) scans due to the dispersive transport characteristics of the charge carriers in the bulk of the SnO 2 . The photo-generated charge carriers are captured and released by the SnO 2 surface states that are close to the conduction band-edge resulting in a very significant variation; this is confirmed by the hysteresis observed in the forward and reverse scan current–voltage measurements under AM1.5 illumination. The hysteresis behavior assures that the charge carriers are accumulated in the bulk of electron acceptor due to the trapping, and released by de-trapping mediated by surface states observed during the forward and reverse scan measurements

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2018

G. Gopakumar, Ashok, A., Vijayaraghavan, S. N., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “MoO3 Surface Passivation on TiO2: An Efficient Approach to Minimize Loss in Fill Factor and Maximum Power of Dye Sensitized Solar Cell”, Applied Surface Science, vol. 447, pp. 554 - 560, 2018.[Abstract]


The present study demonstrates the possibility for improving the performance of dye sensitized solar cell (DSSC) only by minimizing the loss in fill factor (FF) and maximum power point (PMAX) which can be achieved by passivating the nanocrystalline titanium dioxide (TiO2) using physical vapor deposited molybdenum trioxide (MoO3) thin films. The effect of MoO3 coated TiO2 on charge carrier transport was examined in resulting DSSCs and observed that  ∼14% enhancement in efficiency is possible for 5 min passivation of MoO3 on TiO2. The physical vapor deposited MoO3 films were  ∼75% transparent in the spectral range of 350–800 nm with an optical bandgap of  ∼3.1 eV. The wide bandgap MoO3 films facilitate the incoming photons to reach the sensitizing dye to generate excitons. The 14% enhancement in the performance of DSSC by MoO3 passivation is observed through improving only the FF and PMAX while it does not contribute anything significantly to current density and open circuit voltage. Electrochemical impedance spectroscopic studies further confirmed these observations through photo-electron lifetime, which remains constant both in the bulk of pristine TiO2 and MoO3 passivated TiO2 and it further confirms the effect of MoO3 passivation on FF and PMAX in DSSCs.

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2018

A. Ashok, Gopakumar, G., Vijayaraghavan, S. N., Shantikumar V. Nair, and Dr. Mariyappan Shanmugam, “Understanding Hysteresis Behavior in SnO2 Nanofiber Based Dye Sensitized Solar Cell”, Journal of Photovoltaics , 2018.[Abstract]


Tin oxide (SnO2) nanofiber-based dye-sensitized solar cell (DSSC) exhibits an anomalous hysteresis effect on its current–voltage characteristics. While the one-dimensional nature of SnO2 nanofibers is considered facilitating effective charge transport in DSSCs, the surface states present in the SnO2 bandgap are observed to be playing an influential role in trapping and detrapping of charge carriers in the bulk as confirmed by electrochemical impedance spectroscopic studies. Forward and backward electrical bias sweeps identify the hysteresis effect in the performance of resulting DSSCs due to which 43% difference was observed in the photovoltaic performance. Charge carriers generated in the dye utilize the SnO2 nanofiber as a transport medium to reach electrode through energetically active SnO2 surface states which effectively trap and detrap the photogenerated charges during the transport resulting in the hysteresis effect. The observed hysteresis effect varies the maximum power density (PMAX) and fill factor (FF) of the resulting DSSC by 35% and 25%, respectively, between forward and backward scans. The significant change in PMAX and FF asserts that trapping and detrapping mediated charge transport process contributed to the variation in overall performance by 43%.

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2018

A. Ashok, Mathew, S. E., Shivaram, S. B., Dr. Sahadev Shankarappa, Shantikumar V. Nair, and Dr. Mariyappan Shanmugam, “Cost Effective Natural Photo-sensitizer from Upcycled Jackfruit Rags for Dye Sensitized Solar Cells”, Journal of Science: Advanced Materials and Devices, p. -, 2018.[Abstract]


Abstract Photo-sensitizers, usually organic dye molecules, are considered to be one of the most expensive components in dye sensitized solar cells (DSSCs). The present work demonstrates a cost effective and high throughput upcycling process on jackfruit rags to extract a natural photo-active dye and its application as a photo-sensitizing candidate on titanium dioxide (TiO2) in DSSCs. The jackfruit derived natural dye (JDND) exhibits a dominant photo-absorption in a spectral range of 350 nm-800 nm with an optical bandgap of ∼1.1 eV estimated from UV-Visible absorption spectroscopic studies. The \{JDND\} in \{DSSCs\} as a major photo-absorbing candidate exhibits a photo-conversion efficiency of ∼1.1 % with short circuit current density and open circuit voltage of 2.2 mA.cm-2 and 805 mV respectively. Further, the results show that concentration of \{JDND\} plays an influential role on photovoltaic performance of the \{DSSCs\} due to the significant change in photo-absorption, exciton generation and electron injection into TiO2. The simple, high throughput method used to obtain \{JDND\} and the resulting \{DSSC\} performance can be considered as potential merits establishing a cost effective excitonic photovoltaic technology.

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2018

H. Menon, Gopakumar, G., Vijayaraghavan, S. N., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “2D Layered MoS2 Incorporated TiO2 Nanofiber Based Dye Sensitized Solar Cells”, ChemistrySelect , 2018.

2017

A. Ashok, Vijayaraghavan, S. N., Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Molybdenum Trioxide Thin Film Recombination Barrier Layers for Dye Sensitized Solar Cells”, RSC Advances , vol. 7, pp. 48853-48860, 2017.[Abstract]


A physical vapor deposition based molybdenum trioxide (MoO3) thin film is demonstrated as an efficient reverse-electron recombination barrier layer (RBL) at the fluorine doped tin oxide (FTO)/titanium dioxide (TiO2) interface in dye sensitized solar cells (DSSCs). Thin films of MoO3 show an average optical transmittance of ∼77% in a spectral range of 350–800 nm with bandgap value of ∼3.1 eV. For an optimum thickness of MoO3, deposited for 5 minutes, the resulting DSSCs showed 15% enhancement in efficiency (η) compared to the reference DSSC which did not use MoO3 RBL; this suggests that MoO3 is effectively suppressing interfacial recombination at the FTO/TiO2 interface. Further, increasing the thickness of MoO3 RBL at the FTO/TiO2 interface (20 minutes deposition) is observed to impede charge transport, as noticed with 55% reduction in η compared to the reference DSSC. Thin film MoO3 RBL with an optimum thickness value at the FTO/TiO2 interface efficiently blocks the leaky transport pathways in the mesoporous TiO2 nanoparticle layer and facilitates efficient charge transport as confirmed by electrochemical impedance spectroscopy.

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Publication Type: Conference Proceedings

Year of Publication Title

2018

A. Ashok, Gopakumar, G., Shantikumar V. Nair, and Dr. Mariyappan Shanmugam, “FTO/TiO2 Interface Engineering by MoO3 Thin Films for Dye Sensitized Solar Cell Applications”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, Kerala, India., 2018.

2018

G. Gopakumar, Ashok, A., Shantikumar V. Nair, and Dr. Mariyappan Shanmugam, “2D Layered MoS2 Enabled Photo-responsive Characteristics in TiO2 Nanoparticle Film”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, Kerala, India, 2018.

2018

S. N. Vijayaraghavan, Menon, H., Gopakumar, G., Dr. Mariyappan Shanmugam, and Shantikumar V. Nair, “Studies on Charge Transport and Recombination in MoO3 Coated SnO2 Based Dye Sensitized Solar Cells”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, Kerala, India., 2018.

2018

H. Menon, Gopakumar, G., Vijayaraghavan, S. N., Dr. Mariyappan Shanmugam, Ashok, A., and Shantikumar V Nair, “Effect of 2D Layered WS2 Nanoflakes on SnO2 Based Dye Sensitized Solar Cell Performance”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, 2018.

2018

G. Gopakumar, Ashok, A., Shantikumar V. Nair, and Dr. Mariyappan Shanmugam, “Hydrothermal Assisted Heterogeneous MoS2 Enabled Performance Enhancement in Dye Sensitized Solar Cells”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, Kerala, India., 2018.

2018

A. Ashok, Shantikumar V Nair, and Dr. Mariyappan Shanmugam, “Studies on Defect Mediated Charge Transport and Recombination Dynamics in SnO2 Based Dye Sensitized Solar Cells”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, Kerala, 2018.

2018

S. V. K, Ashok, A., Shantikumar V. Nair, and Dr. Mariyappan Shanmugam, “Graphene Quantum Dots Enabled Photoabsorption in Mesoporous TiO2 for Excitonic Solar Cell Application”, Third International Conference on Nanomaterials: Synthesis, Characterization and Applications. Mahatma Gandhi University, Kottayam, Kerala, India., 2018.

2017

G. E. Unni, Nair, S. V., and Dr. Mariyappan Shanmugam, “Two Dimensional SnO2 Nanoplates for Efficient Photo-electron Transport in Excitonic Solar Cells”, Nano India. IIT Delhi, India., 2017.

2017

G. Gopakumar, Menon, H., Nair, S. V., and Dr. Mariyappan Shanmugam, “MoS2 Layered Semiconductor: An Efficient Electron Transport Bridge in Mesoscopic Electron Acceptor for Dye Sensitized Solar Cell Applications”, Nano India. IIT Delhi, India., 2017.

2017

A. Ashok, Unni, G. E., Raghavan, V., Dr. Mariyappan Shanmugam, and Nair, S. V., “Spray Pyrolysis Deposited CdTe/CdS Thin Film Heterojunction for Photovoltaic Applications”, Nano India. IIT Delhi, India., 2017.

Dr. Mariyappan Shanmugam
Asst. Professor, Nanosciences, Center for Nanosciences, Kochi

mshanmugham@aims.amrita.edu