C. Sudha Kartha

Cochin University of Science and Technology, Fort Cochin, Kerala, India

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Publications (129)140.67 Total impact

  • Gincy Sunny, C. Sudha Kartha, K. P. Vijayakumar
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    ABSTRACT: Copper Tin Sulfide (Cu2SnS3), one of the promising absorber layer for thin film solar cell, was successfully deposited on glass substrate maintained at a substrate temperature of 325° C by chemical spray pyrolysis technique (CSP). Variation in copper concentration in the precursor solution affects the structural, optical and electrical properties of the films. XRD results proved the tetragonal structure (with preferential orientation along (112) orientation) of the samples. All samples were p-type and their band gap and resistivity decreased with increase in Copper concentration. A minimum resistivity of 1.6×10-3 Ω.cm was obtained for an optimum copper concentration.
    03/2014; 1591(1).
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    ABSTRACT: SnS thin films were deposited using Chemical Spray Pyrolysis (CSP) technique at a substrate temperature of 415 °C. Resistivity of pristine SnS thin film was 120 Ω.cm. In order to decrease resistivity, in-situ copper doping was done and its effects on the structural, optical and electrical properties were studied. Percentage of Cu was varied as 2%, 4%, 6%, 8% and 10% of tin in the precursor solution. Resistivity decreased with minimum resistivity of 1.6 Ω.cm for the sample doped with 6% copper. Beyond 6 % doping, resistivity increased. All the films were n type irrespective of doping.
    03/2014; 1591(1).
  • M. V. Santhosh, C. Sudha Kartha, K. P. Vijayakumar
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    ABSTRACT: CuInS2/In2S3 heterojunction photovoltaic device was realized in an area of 2.5 × 2 cm2 using automated spray pyrolysis machine which shows an open-circuit voltage of 432mV, short circuit current density of 6.33mA/cm2, fill factor of 34% and efficiency of 0.94%. Performance of the device was monitored up to 100 days and it was working quite well without the application of any protective coatings. The device maintains a fill factor of around 32% up to 80 days but other photovoltaic parameters had slight decrease.
    03/2014; 1591(1).
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    ABSTRACT: CuZnS is an alloy having mixed structure of CuxS and ZnS. Here we studied the structural, optical, compositional and electrical properties of CuZnS films prepared using chemical spray pyrolysis (CSP). Just by varying ratio of Cu to Zn was observed that material can be changed from P type to N type and electrical conductivity can be increased by 4 orders. Increase in concentration of Cu leads to decrease bandgap to 1.8 eV from 3.4 eV. CuZnS films having high concentration of copper can be used as good absorber and weakly doped films as buffer / window layers in solar cells.
    03/2014; 1591(1).
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    ABSTRACT: Effect of spray rate on structural, optical and electrical properties of spray pyrolysed Cu2ZnSnS4 (CZTS) thin films was investigated. We deposited films by varying spray rate from 2 ml/min to 10 ml/min in steps of 2 ml/min. For very low and high spray rates presence of secondary phases could be observed while for the films prepared at a spray rate of 6 ml/min were devoid of secondary phases. As spray rate increases band gap decreased. Samples prepared at 6 ml/min had optimum band gap of 1.5 eV. All the samples were observed to be p-type. Resistivity values increased steadily up to 6 ml/min and then slightly decreased. From the present work, CZTS films prepared at a spray rate of 6 ml/min is found to be ideal for absorber layer in solar cell.
    03/2014; 1591(1).
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    ABSTRACT: Polymer solar cells with configuration ITO/ZnO/P3HT:PCBM/Ag were fabricated using cost effective chemical spray pyrolysis and spin coating techniques. When surface of ZnO layer was modified with a second layer so as to increase the roughness, considerable improvement in cell parameters were observed. Optimum conditions for the required roughness were identified and changes in cell parameters with variation in surface roughness were studied. Major enhancements were observed in the open circuit voltage and in the cell efficiency.
    03/2014; 1591(1).
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    ABSTRACT: XPS depth profile studies were carried out to analyze the composition and stoichiometry of sprayed CZTS thin films giving an efficiency of 1.85% in CZTS based thin film solar cell. Surface layers were nearly stoichiometric (Cu:Zn:Sn:S=2:1:1:4) whereas the inner layers were found to be Copper rich in composition making it electrically more conductive.
    03/2014; 1591(1).
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    ABSTRACT: CuInS2, In2S3 and fluorine doped tin oxide (FTO) thin films were prepared by simple, cost effective Chemical Spray Pyrolysis (CSP) method and effect of [Cu]/[In] ratio on the structural, optical, electrical and morphological properties of CuInS2 thin films were investigated. X-ray diffraction analysis shows that grain size of CuInS2 samples increases with increase in [Cu]/[In] ratio in the spray solution. It could be figured out that CuxS binary phases are absent in the films. Optical studies reveals that the band gap of the films decreases on increasing the [Cu]/[In] ratio. Type of conductivity and resistivity of CuInS2 films were estimated from Hall measurement system. On increasing [Cu]/[In] ratio resistivity decreases. Surface morphology of the films deposited at different spray rates were analyzed using Atomic Force Microscopy (AFM) and results shows that there should be an optimum spray rate for device fabrication and was fixed at 4 ml/min. Surface structure and uniformity were confirmed by employing Scanning Electron Microscopy (SEM). Composition and p-type conductivity of CuInS2 samples were analyzed through Energy Dispersive X-ray analysis (EDX). Finally the optimized CuInS2 films were used for device fabrication. The best device in this study has open circuit voltage of 457 mV and short circuit current density of 5.45 mA/cm2. Efficiency and fill factor were 0.94% and 38% respectively.
    Solar Energy. 01/2014; 108:508–514.
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    ABSTRACT: Consequence of variation in Indium concentration in chlorine doped In2S3 thin films deposited by spray pyrolysis technique was studied. Chlorine was incorporated in the spray solution, using HCl and Indium concentration was varied by adjusting In/S ratio Interestingly, the photo response of all chlorine doped samples augmented compared to pristine samples; but the highest photosensitivity value of ̃2300 was obtained only when 36ml 0.5M HCl was added to the solution of In2S3 having In/S=2/8. It was also observed that samples with high photosensitivity possess higher band gap and variation in sub band gap absoption levels were observed with increase in Indium concentration. The present study proved that concentration of Indium plays an important role in controlling the crystallinity and photosensitivity of chlorine doped samples.
    12/2013; 1576(1).
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    ABSTRACT: Effect of diffusion of Tin in the window layer of CuInS2/In2S3 heterojunction photovoltaic device fabricated using automated spray pyrolysis machine, is presented in this paper. Considerable improvement in the device parameters was observed through this process. The best device obtained in this study had open-circuit voltage of 370mV, short circuit current density of 5.33mA/cm2, fill factor of 32% and efficiency of 0.65%.
    12/2013; 1576(1).
  • D. R. Deepu, C. Sudha Kartha, K. P. Vijayakumar
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    ABSTRACT: Fluorine doped tin oxide (FTO) thin films were prepared by using automated Chemical Spray Pyrolysis (CSP) machine and the effect of concentration of the precursors on the conductivity and transmittance of the films were studied. The resistivity (ρ) and mobility (μ) are in the range of 10-3-10-4 Ω-cm and 8.2-13.5 cm2V-1s-1 respectively. The electron density lies between 3.4 × 1020 and 6.6×1020 cm-3. The film transmittance varies between 70 to 80% and the films shows very good reflectivity in the IR-NIR region. Prepared films can be used as transparent electrodes in photo voltaic and optoelectronic devices.
    12/2013; 1576(1).
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    ABSTRACT: Thin film solar cells were fabricated using CuInS2 as absorber layer and CdS as buffer layer. CuInS2 and CdS layers are deposited using chemical spray pyrolysis and chemical bath deposition respectively. Proper movement and collection of generated carriers really affect the performance of the cell. Introduction of a very thin layer of silver doped ZnO (ZnO:Ag) window layer between the buffer layer and ITO improves performance of the cell, with open circuit voltage of 409mV, short circuit current density of 2.89 mA/cm2, fill factor of 44.3% and conversion efficiency of 0.52%.
    12/2013; 1576(1).
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    ABSTRACT: Photoluminescence in the characteristic blue-green region of the spectrum was emitted by zinc oxide (ZnO) thin films grown by chemical spray pyrolysis. We have been able to optimize spray rate and substrate temperature to obtain ZnO thin films with emission centered at ∼383 nm and ∼517 nm, respectively. We also observed that Al-doped ZnO films resulted in improved radiative efficiency of the near-band-edge emission; optimized Al-doped spray deposited thin films emitted only blue light.
    Materials Science in Semiconductor Processing 04/2013; 16(2):326–331. · 1.34 Impact Factor
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    ABSTRACT: This work projects photoluminescence (PL) as an alternative technique to estimate the order of resistivity of zinc oxide (ZnO) thin films. ZnO thin films, deposited using chemical spray pyrolysis (CSP) by varying the deposition parameters like solvent, spray rate, pH of precursor, and so forth, have been used for this study. Variation in the deposition conditions has tremendous impact on the luminescence properties as well as resistivity. Two emissions could be recorded for all samples—the near band edge emission (NBE) at 380 nm and the deep level emission (DLE) at ~500 nm which are competing in nature. It is observed that the ratio of intensities of DLE to NBE (/) can be reduced by controlling oxygen incorporation in the sample. - measurements indicate that restricting oxygen incorporation reduces resistivity considerably. Variation of / and resistivity for samples prepared under different deposition conditions is similar in nature. / was always less than resistivity by an order for all samples. Thus from PL measurements alone, the order of resistivity of the samples can be estimated.
    International Journal of Photoenergy 02/2013; 2013. · 2.66 Impact Factor
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    ABSTRACT: Photoluminescence (PL) technique was used to identify defect levels in Copper Zinc Tin Sulphide (CZTS) thin films deposited using Chemical Spray Pyrolysis (CSP). Films were deposited for different Cu:Zn:Sn:S ratios. An emission was observed at 0.8 eV. It was monitored from 15K to room temperature and activation energy was calculated. Excitation power dependent studies were done to analyze the type of transition.
    02/2013;
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    ABSTRACT: Cu2ZnSnS4 (CZTS) thin films were prepared using chemical spray pyrolysis technique on soda lime glass (SLG) substrates. The effect of tin concentration on the structural, optical and electrical properties was investigated. We deposited films by varying tin concentration from 0.007 M to 0.013 M in steps of 0.0015 M keeping the concentration of copper, zinc and sulphur at 0.02 M, 0.01 M and 0.12 M respectively. It was found that crystallinity of the film increased up to the tin concentration of 0.01 M and then decreases. Band gap of the films steadily decreased from 1.48 to 1.26 eV with increase in tin concentration. All the samples were observed to be p-type by hot probe method. Resistivity of the films increased with increase in tin concentration. In this work we tuned the optoelectronic properties by varying the tin concentration alone and optimized the concentration of tin which yields samples ideal for photovoltaic applications.
    02/2013;
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    ABSTRACT: The present work reports the influence of indium concentration and annealing temperature (100–400 °C) on the structural and optoelectronic properties of indium selenide thin films grown using a stack elemental layer technique. The concentration of indium in indium selenide thin films is varied by adjusting the thickness of the indium layer to 28, 42 or 56 nm while keeping the selenium layer thickness constant at 200 nm. Depending on the indium layer thickness of 42 or 56 nm, indium selenide thin films exhibited a phase transition either from a mixed phase (InSe, γ-In2Se3 and β-In2Se3) and/or from a complete amorphous phase to a single phase γ-In2Se3 at annealing temperature 400 or 300 °C, respectively, with a preferential grain orientation along the c-axis. Depth-wise X-ray photoelectron spectroscopy (XPS) analysis conducted on these samples (thickness of Se = 200 nm, In = 56 nm) showed evidence of a phase transition from amorphous to crystalline γ-In2Se3 phase and formation of uniform stoichiometric (In/Se = 40:60) indium selenide. On the other hand, indium selenide grown using an indium thickness of 28 nm did not exhibit any phase transition. While using X-ray diffraction (XRD) studies to analyse the structural properties, we made use of optical absorption and Raman spectroscopy in order to determine the optical energy gap and find the presence of parasitic β-In2Se3 phase, respectively. The growth along the c-axis either gives rise to carrier diffusion along the c-axis or causes the appearance of a higher photosensitivity (62–72) due to the absence of dangling bonds which trap photogenerated carriers. The properties exhibited by the c-axis-grown γ-In2Se3 suggest the potentiality of this material as a window layer in solar cell application.
    physica status solidi (b) 01/2013; 250(1):95-102. · 1.49 Impact Factor
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    ABSTRACT: In2S3 thin films have been grown on Indium Tin Oxide (ITO) by Chemical Spray Pyrolysis. The structural and physical–chemical properties of the films have been investigated by means of X-ray Diffraction and X-ray Photoelectron spectroscopy (XPS). The valence band discontinuity at the In2S3/ITO interface has been determined by XPS resulting in a value of 1.9 ± 0.2 eV. Consequently, the conduction band offset has been estimated to be 1.0 ± 0.4 eV.
    Thin Solid Films 07/2012; 520(18):5856–5859. · 1.87 Impact Factor
  • Source
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    ABSTRACT: The origin of various defect levels in the SnS thin films deposited using chemical spray pyrolysis (CSP) technique has been explored in this manuscript, by employing low-temperature photoluminescence (PL) technique. Concentration of Sn in the samples was varied purposefully by ex situ diffusion in order to alter the defect levels. The acceptor level obtained at 0.22 eV from the Arrhenius plot, has been assigned as the defect level caused by the Sn vacancies present in the lattice. Two shallow donor levels are conclusively identified and their activation energies have been estimated. The present study could also unearth a trap level in the forbidden energy gap which was due to the oxygen contaminant occupied by the vacancy of Sn. This trap level could be removed by annealing the sample in vacuum or through the ex situ diffusion of Sn. Employing Kelvin probe force microscopy (KPFM), the work-function of SnS was obtained as 4.925 eV, from which the position of the Fermi level could be assigned. Based on the present work, an energy level scheme for SnS thin films is proposed outlying origin of various defect levels.
    physica status solidi (a) 07/2012; 209(7):1274-1278. · 1.21 Impact Factor
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    ABSTRACT: Samples were deposited using chemical spray pyrolysis technique by varying the pH of the starting precursor solution from 0.8 to 3.2. These samples were analyzed using X- ray diffraction, optical absorption spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, and electrical measurements in order to investigate the role of pH of the precursor solution on structural, morphological, electrical and optical properties of the SnS films. From the study we could optimize the pH of precursor solution required for the deposition of device quality SnS thin films. Resistivity of the films was brought down by three orders (to 6 × 10−2 Ω cm) along with enhancement in grain size as well as photosensitivity by optimizing the pH of the precursor solution alone. Band gap of the films could also be tailored by controlling the pH of the precursor solution.
    Applied Surface Science 07/2012; 258(18):6870–6875. · 2.54 Impact Factor

Publication Stats

326 Citations
140.67 Total Impact Points

Institutions

  • 1986–2014
    • Cochin University of Science and Technology
      • • Department of Physics
      • • Department of Polymer Science and Rubber Technology
      Fort Cochin, Kerala, India
  • 2000–2010
    • Iwate University
      Morioka, Iwate, Japan
  • 2009
    • University of Calcutta
      Kolkata, Bengal, India