Pelin Kavak

Nano-crystal V2O5nH2O sol-gel films made by dip coating

Vanadium pentoxide (V2O5) sols were formed through a reaction of V2O5 powder with hydrogen peroxide (H2O2); the solution evolves in time, beginning from diperoxo species, decavanadic acid spedies at intermediate step and finally polymerization of V2O5 nH2O sols. From the sols, V2O5 thin films were succesfully fabricated on indium-tin-oxide (ITO) coated and corning glass substrates by sol-gel dip coating method. X-ray diffraction pattern of the films at hand exhibited a series of (00l) peaks that confirmed both some preferred orientation of a layered structure in one dimension stacking of ribbons perpendicular to the substrate and ability of employed method to produce nano crystal of V2O5 nH2O sol-gel films. The basal distance,d, (increased with an amount of water in the sols in steps of 2.8 A, attributed van der Walls water molucule diameter), was determined as 10.6-17.2 A that corresponded n in between 2-6. On the other hand, the average particle sized, D, of the precipitated nanocrystals were calculated through Sherrers formula and determined around 15-28 nm that consisted with AFM and SEM analysis. The electrochemical studies by cyclic voltametry showed the Li + intercalation capacity, reversibility and stability. Finally, the simultaneous TG and DTA on the as prepared films indicated two stage mass loss.

Influence of water expulsion on structural properties of V2O5nH2O sol-gel films

Vanadium pentoxide (V2O5) thin films were prepared by dip-coating sol-gel technique by dissolving V2O5 powder in hydrogen peroxide (H2O2), the solution, leading V2O5 sol-gel nanocrystalline films. The films under preparation were exposed different hydration states, n, varying from 6 to 2 determined via XRD measurements. Water molecules were adsorbed in layered structure of V2O5 oxide films and hence the adsorption could be described as an intercalation in which the molecules were trapped in some cavities and were not randomly oriented. (00l) pattern of X-ray diffraction analysis not only approved the one dimensional stacking of V2O5 ribbons but also served to determine basal distance from which hydration state was guessed. The basal distance were calculated from the position of 00l peak and varied from 17.2 A to 10.6 A that corresponded to n=6 to n=2 respectively. During the water departure upon heating, the basal distance reduced by steps of 2.8 A (diameter of vander Walls water molecule) towards 8.8 A v...

Ionic conduction in different hydrated V2O5 film

Because of the layered structure of vanadium pentoxide films (V2O5), approved by XRD measurement, sensitized from different hydrated V2O5.nH2O sols, demonstrated anisotropic conductivities in current voltage (I-V) measurement. Conductivity values, originated from electronic and ionic conductions, differed provided that measurements were performed in a direction parallel to the ribbons rather than perpendicular to them. The overall electrical conductivity of V2O5nH2O sols mainly depended on the hydration state n and the amount of reduced V4+ ions in which n was determined around 4-6 [1] from the basal distance (17.6 A) through XRD measurement while V4+ ions were determined through FTIR analysis. Electronic conduction prevailed in dehydrated V2O50.5H2O sols whereas non-stoichiometric vanadium pentoxide was a mixed-valence compound and its electronic properties arised from electron hopping between V4+ and V5+ ions so-called “small polaron model”. Indeed, reduction/oxidation peaks in lithium (Li+) intercalati...

Investigation of Indoor Stability Testing of Polymer Solar Cell

We have fabricated organic solar cell of a new low bandgap polymer poly[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl-alt-4,7-bis(2-thienyl)-2,1,3-benzothiadiazole-5′,5′′-diyl] (PCPDTTBTT). We have investigated for the first time the stability tests, ISOS-L-1 and ISOS-D-3, of PCPDTTBTT solar cells. Thermal annealing of PCPDTTBTT solar cells at 80°C brought about an improvement of photocurrent generation, stability, and efficiency of the solar cells. T80 value of PCPDTTBTT solar cell is about 150 hours which is close to P3HT (235 h). PCPDTTBTT is very promising polymer for both polymer solar cell efficiency and stability.

Admittance analysis in (PPE-PPV) polymer (AnE-PVstat) light emitting diodes

In this work, admittance analysis of organic light emitting diode (OLED) (anode/active layer/cathode) was performed at room temperature within the frequency range of 1 kHz-1MHz to find out transport properties of both injected carriers from each side. Moreover, by proper chosen metals, electron or hole only OLED devices were prepared and the measurement was resumed to identify the governed transport path of injected carrier. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output and onset of negative capacitance took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer. The proposed analytical model for admittance, derived for the frequency dependent space charge limited behavior leading negative capacitance issues, was applied on the measured data for the present OLED device.

Electroluminescence property of organic light emitting diode (OLED)

Transport properties of electrons and holes were investigated not only in a anthracene-containing poly(p-phenylene-ethynylene)- alt - poly(p-phenylene-vinylene) (PPE-PPV) polymer (AnE-PVstat) light emitting diodes (OLED) but also in an ITO/Ag/polymer/Ag electron and ITO/PEDOT:PSS/polymer/Au hole only devices. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer.

Current-voltage analysis of PCBM:PCDTBT blend to find out charge transport path

Transport path(s) of charge carrier were identified through I-V measurement within the structure of ITO/PEDOT:PSS/PCDTBT:PCBM/TiOx/Ca/Ag in which ohmic regime was enrolled in low bias side while space charge limited conduction mechanism governed at high bias side. Moreover, influence of each constitituent parts of the present device on the dc transport properties was investigated by preparing ITO/PEDOT:PSS/PCDTBT/Ca/Ag and ITO/PEDOT:PSS/ PCBM/Ca/Ag structures and repeating the mentioned experimental techniques.

Energy-band diagram of PCDTBT, PCBM and blend by cyclic voltammetry and UV-visible measurements

By combination of Cyclic Voltammetry with transmission/absorption measurements, energy-band diagram of PCDTBT, PCBM, and PCDTBT:PCBM blend in ratio of (1:4) was constructed successfully.