[Show abstract][Hide abstract] ABSTRACT: in the present study we focus on the effect of donor/acceptor composition on the conjugation and ordered
structure of the donor-polymer in the most common organic solar cell based on a bulk heterojunction of regioregular poly(3-
hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). In addition, we try to illustrate the effect
of composition, over a wide range, on the internal energy configuration and energy gaps of the donor polymer and acceptor
fullerene in the solar cell active layer. Through the present investigations, we detected an improvement in conjugation
length and ordered structure of the P3HT molecules under the increase its concentration in the solar cell active layer. This
improvement is revealed through red shift of the P3HT absorption peak in optical absorption spectroscopy. In addition, we
found a relation between energy gab and composition of the P3HT:PCBM combination, where the energy gaps of both
P3HT and PCBM increase with increasing P3HT concentration in the solar cell active layer. The higher concentrations of
P3HT or PCBM are the responsible for determining the energy gaps of the molecules in solar cell active layer, while the
large variation in the energy gap of a molecule is a result of its poor concentration in the solar cell active layer. The device
performance parameters are investigated under the wide composition range of P3HT:PCBM solar cell active layer. The best
(optimized) solar cell composition in these investigations is the 50:50 wt.% of the P3HT:PCBM binary at which the JSC,
VOC, FF, and PCE are 6.3 mA/cm2
, 0.59 V, 0.55, and 2.03 %, respectively.
[Show abstract][Hide abstract] ABSTRACT: Bulk ZnO nanorod assemblies have been successfully fabricated on CuO nanowires through spin coating of organoprecursor gels. A thin film of CuO nanowires was first generated by direct heating of a metallic Cu-foil at 500 °C in an air atmosphere. A stable colloidal organo-precursor sol synthesized by dissolving equimolar zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol was subsequently repeatedly deposited onto the CuO nanowires by spin coating. The formation of ZnO nanorod assemblies was controlled by varying the number of coatings. The average diameter of the ZnO rods was determined to be ∼600 nm.
[Show abstract][Hide abstract] ABSTRACT: We report single layer to few layer graphene on polycrystalline nickel by chemical vapor deposition at ambient pressure using solid precursor, camphor. Investigating at a wide range of temperature, it was observed that 870 °C is better for the deposition of single layer graphene on nickel substrate. The percentage of single layer on the substrate reduced significantly with decreasing the deposition temperature. The full width half maximum of the synthesized single layer graphene was 21 cm−1 and Raman intensity ratio of 2D to G peak was almost nine. The film was transferred to insulating substrate and measured transmittance was 85 %. Raman spectroscopy, Raman mapping, SEM and UV–visible spectrometer measurement were performed for characterization.
Journal of Materials Science Materials in Electronics 06/2013; 24(6). DOI:10.1007/s10854-013-1073-x · 1.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have fabricated bulk heterojunction organic solar cells using coumarin 6 (C6) as a small organic dye, for light harvesting and electron donating, with fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), acting as an electron acceptor, by spin-coating technique of the blend solutions. We have studied effect of PCBM concentration on photocurrent and performance parameters of the solar cells. We found that the optical absorption of the dye increased with increasing its concentration in the active layer blends. The higher concentrations of PCBM in active layer enhanced the photocurrent of the solar cells, as a result of improving charge carrier separation and electron transport in solar cell active layer. The improved charge carrier separation between C6, as a donor, and PCBM, as an acceptor, was indicated through the formation of bulk heterojunction by blending C6 with PCBM. The formation of C6:PCBM bulk heterojunction blend was confirmed through the symbatic behavior of the corresponding solar cell and, also, through the homogeneity and smoothing in the atomic force microscopy images of the C6:PCBM blend films. For the same reasons, the performance parameters of the C6:PCBM solar cell improved by modification of the PCBM concentration in the solar cell active layer.
[Show abstract][Hide abstract] ABSTRACT: We report the synthesis of single-layer graphenes on polycrystalline Ni foils by alcohol-based chemical vapor deposition (CVD) with IR-lamp heating. Heating with an IR lamp allows fast cooling and a reduction in the overall CVD time because of the rapid thermal processes in the heating and cooling stages. Spatially resolved Raman spectroscopy shows that single-layer graphenes are synthesized by CVD of alcohol with IR-lamp heating. The effects of the reaction temperature and alcohol type on the number of layers and graphene quality are investigated.
[Show abstract][Hide abstract] ABSTRACT: We have studied the effects of ambient Helium gas pressure on the optical, structural and physical properties of the diamond like carbon thin films using a camphoric carbon (CC) soot target, deposited by pulsed laser ablation. Both the optical gap and electrical resistivity are found to increase with 2.6 Torr leads to a decre ase in optical gap and electrical resistivity. The films are further investigated by different spectroscopic techniques such as, Raman, XPS and FTIR spectroscopy, and surface morphological techniques like SEM and AFM. Improvement of the opto-electrical and structural properties of the diamondlike carbonaceous films deposited in helium environment using CC soot target reveal different behaviour than reported earlier.
International Journal of Modern Physics B 05/2012; 16(06n07). DOI:10.1142/S0217979202010531 · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amorphous carbon nitride films (a-CNx) were deposited by pulsed laser deposition of camphoric carbon target with different substrate temperatures (ST). The influence of ST on the synthesis of a-CNx films was investigated. The nitrogen-to-carbon (N/C) and oxygen-to-carbon (O/C) atomic ratios, bonding state, and microstructure of the deposited a-CNx films were characterized by X-ray photoelectron spectroscopy and were confirmed by other standard measurement techniques. The bonding states between C and N, and C and O in the deposited films were found to be significantly influenced by ST during the deposition process. The N/C and O/C atomic ratios of the a-CNx films reached the maximum value at 400°C. ST of 400°C was proposed to promote the desired sp3-hybridized C and the C3N4 phase. The C–N bonding of C–N, C=N and C≡N were observed in the films.
[Show abstract][Hide abstract] ABSTRACT: Hard and smooth nanocrystalline diamond (NCD) thin films were deposited on polished silicon substrates by biased enhanced growth in microwave plasma chemical vapor deposition. The films deposited with varying the methane concentration and biasing voltage were characterized by Raman spectroscopy, nano-indenter, x-ray diffraction and atomic force microscopy. Stress in the films increases with decreasing methane concentration in the gas-phase and with increasing biasing. The adhesion between NCD film and Si substrate is very strong sustaining the compressive stress as high as high as 85 GPa. It was hypothesized that hydrogen content of the films and graphitic content of the films are responsible in generating stress. The hardness is well correlated with the Raman peak intensity ratio of NCD peak to G peak.
International Journal of Modern Physics B 05/2012; 16(06n07). DOI:10.1142/S021797920201049X · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: gas ambient with varying substrate temperature from 20°C to 500°C. The effects of the substrate temperature and ambient nitrogen gas pressure on the surface morphology, composition, structure, and electrical properties of the nitrogen incorporated camphoric carbon thin films have been investigated by standard techniques. We found that the amorphous structure of CNx films can be changed by substrate temperature and the CNx films with high nitrogen content have relatively high electrical resistivity.
International Journal of Modern Physics B 05/2012; 16(06n07). DOI:10.1142/S021797920201052X · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the efficient photoluminescence (PL) and optical properties of hydrogenated amorphous carbon thin films codoped with nitrogen and trimethylboron (TMB) grown by rf plasma-enhanced chemical vapor deposition at room temperature. The study clearly shows the observation of discrete PL emission peaks. The PL intensity of the film deposited with 20 sccm TMB is more than 103 times than that of the film deposited without TMB. The change of optical bandgap and PL emission energy with TMB flow rate are discussed based on sp3 and sp2 C networks. Angular dependence of the PL spectra revealed that the origin of multiple sharp peaks is due to Fabry-Perot cavity interference effect.
International Journal of Modern Physics B 05/2012; 16(06n07). DOI:10.1142/S0217979202010920 · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Raman scattering analysis revealed that the structure of carbon (C) films prepared by pulsed laser deposition at room temperature is predominantly amorphous and the structure of amorphous C nitride (a-CNx) films can be changed with varying substrate temperatures (ST) from 20 to 500°C. The deposited a-CNx films are composed of C–N, C≡N and C–O bonded materials and the C–N and C≡N bonds are increased with ST. We have found no other obvious peaks that can be distinguished in the range of 900 to 2300 cm-1 in which several peaks always appear in a-CNx films. The spectra were deconvoluted into Raman D and G peaks and the structural parameters were determined. The upward shifts of Raman G peak towards 1592 cm-1 show evidence of a progressive formation of crystallites in a-CNx films upon increase of ST, while the upward shifts of Raman D peak towards 1397 cm-1 have been related to the decrease of bond-angle disorder and sp3 tetrahedral bonding in its structure. Raman FWHM and ID/IG also indicate that N incorporation with increase of ST caused an increase in the number and/or size of graphitic domains in the a-CNx films.
[Show abstract][Hide abstract] ABSTRACT: Transparent conductive thin films of single-wall carbon nanotubes (SWCNTs) doped with organic dopant molecules encapsulated inside the SWCNTs are reported. Doping with tetrafluorotetracyano-p-quinodimethane encapsulated within the SWCNTs improved the ratio of direct current to optical conductivity in the SWCNT thin films by a factor of about 1.8. Thermal stability of the improvement in electrical conductivity by encapsulation doping is investigated as a function of annealing temperature. We found that encapsulation doping provides stable conductivity enhancement in transparent thin films of SWCNTs compared to doping by adsorbed dopant molecules outside the SWCNTs.
[Show abstract][Hide abstract] ABSTRACT: We present an improved preparation method for the growth of high quality crystals of cuprous oxide films grown by thermal oxidation of cupper foils with water vapor. This method proved to be good for preparing cuprous oxide films with high purity and large grain size. X-ray diffraction studies revealed the formation of Cu2O films with preferred (111) orientation. The cuprous oxide diodes fabricated by the above technique have been studied using current–voltage method.
Thin Solid Films 01/2012; 520(7):2679–2682. DOI:10.1016/j.tsf.2011.11.037 · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have studied the influence of the methane gas (CH4) pressure on the surface morphology, composition, structural and electrical properties of nitrogenated amorphous carbon (a-C:N) films grown by surface wave microwave plasma chemical vapor deposition (SWMP-CVD) using Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Auger electron spectroscopy (AES), X-rays photoelectron spectroscopy (XPS), UV-visible spectroscopy and 4-point probe resistance measurement. We have succeeded in growing a-C:N films using a novel method of SWMP-CVD at room temperature and found that the surface morphology, bonding, optical and electrical properties of a-C:N films are strongly dependent on the CH4 gas sources and the a-C:N films grown at higher CH4 gas pressure have relatively high electrical conductivity.
International Journal of Modern Physics B 01/2012; 19(05). DOI:10.1142/S0217979205029377 · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thin films of amorphous carbon (a-C and a-C:H) have been deposited using different carbon precursor materials such as camphor - a natural source, graphite and CH4/H2 mixture by different deposition methods, such as ion beam sputtering, pyrolysis, pulsed laser deposition and r.f. plasma CVD. The films are subjected to various standard characterization techniques in order to tailor the required structural and opto-electrical properties for device applications. The effects of deposition parameters and annealing temperatures on the properties of carbon thin films have been investigated. Both p- and n- type of carbon films have been obtained either through controlling the deposition parameters of a particular method or by doping. Solar cells of various configurations, such as n-C/p-Si, p-C/n-Si and n-C/p-C/p-Si, have been fabricated and their photoresponse characteristics are studied. An efficiency of 1.52% has been obtained, so far, for the cell of configuration n-C/p-C/p-Si. Effects of substrate temperature on the photovoltaic properties are also outlined in brief.
International Journal of Modern Physics B 01/2012; 14(02n03). DOI:10.1142/S0217979200000200 · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The phosphorus doped n-type (n-C:P) carbon films and fabrication of n-C:P/p-Si heterojunction solid-state solar cells by pulsed laser deposition (PLD) technique at room temperature using graphite target have been studied. The P atoms incorporated in the films were determined by X-ray photoelectron spectroscopy (XPS) to be in the range of 0.22–1.77 atomic percentages. The cells performances have been given in the dark I–V rectifying curve and I–V working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm2, 25°C). The open circuit voltage (Voc) and short circuit current density (Jsc) for the cells are observed to vary from 215 to 265 mV and from 7.5 to 10.5 mA/cm2, respectively. The cell fabricated using the target with the amount of P by 7 weight percentages (Pwt%) shows the highest energy conversion efficiency, η=1.14% and fill factor, FF=41%. In this paper, the dependence of P content on the electrical and optical properties of the deposited n-C:P films and the photovoltaic characteristic of the n-C:P/p-Si cells are reported.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen-doped amorphous carbon (a-C:N) thin-films have been deposited on novel heat tolerant flexible plastic substrates by a newly developed microwave surface wave plasma chemical vapor deposition (MWSWP-CVD) method. Methane gas and also camphor dissolved with ethyl alcohol gas composition have been used as plasma source. Nitrogen gas has been used as a dopant material for a-C:N films. In this paper, the optical characteristics of absorption coefficients and band gaps for a-C:N are discussed. The optical band gap of a-C:N films was found to be approximately 1.7 eV, which is close to the suitable band gap for solar cell. The optical band gap of a-C:N was found to be dependent on the composition gas source pressures.
[Show abstract][Hide abstract] ABSTRACT: Nitrogenated diamond-like carbon films have been deposited on glass and p-type Si (100) substrates by radio frequency (r.f.) plasma-enhanced chemical vapor deposition (PECVD) with a frequency of 13.56 MHz at room temperature using CH4 as precursor of carbon source and H2 as a carrier gas. The deposition was performed at a different flow rate of nitrogen from 0 to 12 sccm under a constant r.f. power. The effect of nitrogen incorporation on the bonding states and growth kinetics of the deposited films have been investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy and optical properties by UV spectroscopy measurement. Our experimental results show that the incorporation of nitrogen has a considerable effect on the properties of the deposited films. FTIR spectra show that the nitrogen is bonded to carbon and hydrogen as C=N, C≡N, N–H and C–H bonding configurations in the as-deposited film. The incorporation of nitrogen is found to shift the Raman G peak toward the higher wave number and to increase the Raman ID/IG ratio demonstrating the graphitic character of the hydrogenated amorphous carbon–nitrogen films. Band gap is found to reduce with the increase in nitrogen concentration.
Surface Review and Letters 01/2012; 13(01). · 0.38 Impact Factor