Prevent The Back Transfer Of Electrons Biology Essay

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Soon hyung kang et al. reported Columnar-structured rutile TiO2 film having thickness of 1.4micrometer is fabricated using the radio-frequency magnetron sputtering process, for dye-sensitized solar cells (DSSCs). Successive substrate heating to 623K induced the growth of a rutile TiO2 film had specific direction in the (1 1 0) plane, which results in a decrease in the average grain size, caused in an increase of dye uptake, contributes to enhancement of the photocurrent in the DSSC. Pure rutile TiO2 photoelectrode exhibited a Voc of 0.687 V, a Jsc of 6.12mAcm−2, a fill factor of 57.1%, and an efficiency of 2.4%, whereas the anatase TiO2 electrode gives a Voc of 0.745 V, a Jsc of 3.71mAcm−2, a fill factor of 64.2%, and an efficiency of 1.78%. hence, approximately 35% enhanced conversion efficiency is attained with pure rutile TiO2 film. The growth and morphological control of a pure rutile TiO2 film using the RF-magnetron sputtering method enhanced the performance of DSSCs, compared with a pure anatase TiO2 film. Resulted that the columnar-structured rutile TiO2 film prepared by the RF-magnetron sputtering method can be successfully used as a working electrode to enhance the charge-collection efficiency of the DSSC.

[2] Soon Hyung Kang, Moon-Sung Kang, Hyun-Sik Kim, Jae-Yup Kim, Young-Hoon Chung,

William H. Smyrl, Yung-Eun Sung,, Columnar rutile TiO2 based dye-sensitized solar cells by radio-frequency magnetron sputtering, Elsevier , Journal of Power Sources 184 (2008) 331-335.

Khalil [3] discussed fabrication procedures, optical and electrical characterization of NDSSC using natural dyes extracted from Henna (Lawsonia inermis L.), pomegranate, cherries and Bahraini raspberries (Rubus spp.). Factors limiting the operation of the DSSC are also discussed. Doctor blade technique was adopted in deposition of TiO2 suspension. Natural Dyes extracts have been optically analysed by calculating their absorbance using dual beam UV-VIS spectrophotometer and found maximum efficiency 1.076% in case of pomgrante juice and 0.309% using raspberries On the average, the active area of the photovoltaic cell is about 3cm2.

Generally. SEM and X-ray diffraction analysis confirmed the preparation of nanocrystalline TiO2 particles of sizes less than 50 nm .it is found that the formation of nanocrystalline TiO2 particles is greatly affected by TiO2 suspension making procedures as well as by the annealing temperature. The porosity of the TiO2 is an essential not only to ensure high roughness factor, but also to enhance the penetration of the redoxing ions into the film. It was found that a sintered TiO2 film at temperatures lower than the recommended 450°C resulted in cells that generate negligible electric current even in μA . Moreover, TiO2 film degradation in this case was fast and cracks form after a short period of time when the cell is exposed to illumination.

[3] Khalil Ebrahim Jasim, Natural Dye-Sensitized Solar Cell Based on Nanocrystalline TiO2, Sains Malaysiana 41(8)(2012): 1011-1016.

Ding Ren et al. [4] prepared TiO2 thin films for DSSC using reactive medium frequency magnetron sputtering deposition technique. Two sets of films were deposited respectively by altering the tilted angle of the substrate and the total pressure. Scanning electron microscopy and spectroscopic ellipsometry measurements were used to analyzed the deposited TiO2 films. Ren concluded that gradual increase in the oblique angle and in the total pressure were both effective in growing the porosity of the TiO2 films. With gradual increase in the oblique angle 0 to 70 during TiO2 film deposition, the porosity of TiO2 films monotonically increased. With varying the total pressure during Deposition from 1.0 Pa to 4.0 Pa, the porosity of the TiO2 film increased rapidly.

[4] Ding Ren, Yu Zou, ChangYong Zhan and NingKang Huang, Study on the Porosity of TiO2 Films Prepared by Using Magnetron Sputtering Deposition, Journal of the Korean Physical Society, Vol. 58, No. 4, April 2011, pp. 883_885

Giuseppe Calogero et al. [5] studied the photoelectrochemical properties , influence of pH and co-absorbers on natural dyes. He used natural dyestuffs containing betalains and anthocyanins as sensitizers in NDSSC and investigated that the dyes extracted from grape, mulberry, blackberry, red Sicilian orange, Sicilian prickly pear, eggplant and radicchio have shown a unicolor incident photon to current efficiency (IPCE) ranging from 40% to 69%.Short circuit photocurrent densities (Jsc) up to 8.8 mA/cm2, and open circuit voltage (Voc) ranging from 316 to 419 mV, were found from these natural sensitizers under 100 mW/cm2 (AM 1.5) virtual sunlight. The best solar conversion efficiency of 2.06% was attained with Sicilian prickly pear fruits source. Calogero investigated that in specific, the use of raw betalains, having great concentration of betaxantins, provides a promising result transforming 2.06% of 1 sun of light power into electric current. The existence of carboxylic groups in the betalains presents, together with the higher oxidation potential, a benefit for anchoring the dye to the semiconductor and to react better with the iodine/iodide redox couple. The addition of organic co-absorbers and the pH variation improved the current density value, formed by DSSCs sensitized with natural dyes. The use of pyridine enhanced the Voc of the DSSCs sensitized by antocyanins but, at the same time, resulted in a decrease of Jsc.

[5] Giuseppe Calogero, Jun-Ho Yumb, Alessandro Sinopoli, Gaetano Di Marco,Michael Gra¨tzel , Mohammad Khaja Nazeeruddin, Anthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cells, Elsevier, Solar Energy 86 (2012) 1563-1575.

Ying li et al. [6] to observed the photoelectrochemical peak conditions for red cabbage extract as natural sensitizer to fabricate a natural dye-sensitized solar cells (NDSSC). Red cabbage extract were characterized by electrochemical impedance spectroscopy (EIS), UV-Vis and cyclic voltammetry (CVs). Li fabricated NDSSC from a combination of relatively popular materials containing TiO2 photo electrode, natural dye, electrolyte containing I−/I3− redox mediator, and counter electrode. The usage of right pH for red cabbage increases the DSSC performance. He resulted that the increase of efficiency due to the sanitized and absorbed time of natural dye content greatly amplified the specific activity and total load volume. UV-Vis studies showed the absorption band of red cabbage extract solution. Absorption spectrum also indicated that dye from red cabbage extract is found to be highly absorbing at high concentrations. The red cabbage extract provided the sensitizer for dye. The TiO2/ITO electrode was absorbed in natural dye solution 24 h, light source Xe lamp 100 mWcm-2 ,AM 1.5 indicated highest efficiency 2.908% photosensitive for DSSC.

[6] Ying Li, Shu-Hao Ku, Shen-Ming Chen, M. Ajmal Ali, Fahad M. A. AlHemaid,Photoelectrochemistry for Red Cabbage Extract as Natural Dye to Develop a Dye-Sensitized Solar Cells, Int. J. Electrochem. Sci., 8 (2013) 1237 - 1245.

Al hamed et al. [7] investigated Optical and structural properties of several types of natural dyes belonging to Anthocyanin such as Raspberries, Shami-berries, Grapes, Hibiscus, Chlorophyll and a combination of dyes with different ratios and compositions to be used as photo-sensitizer in natural Dye Sensitized Solar Cell. Samples have been made by using SOL-GEL method in fabricating thin film components FTO/TiO2 / Natural Dye / Electrolyte / Pt / FTO for Natural dye sensitized solar cell. Optical analysis of dyes solutions was made using UV-VIS spectroscopy. Absorption spectra indicated the existence of distinctive absorption peaks in the visible region for each type of dye. Transmission spectrum of the dye solutions exhibited good transmittance in the green region (520nm , 570 nm).

The efficiencies for all types of natural dyes used have been tried ,The DSSC fabricated by means of a combination of Raspberries, Hibiscus, Chlorophyll by the ratio (1:1:1) as sensitizer, showed the better photovoltaic efficiency as compared to other single dyes because of the increased sensitivity of the solar cell with total optical absorption for all different types of these dyes. The efficiency of DSSC prepared was η = 3.04%, the fill factor FF = 60% for cell area a = 4cm2, short circuit current JSC = 0.6 mAcm-2 and open circuit voltage Voc = 0.42 V.

[7] Mounir Alhamed, Ahmad S. Issa, A. Wael Doubal STUDYING OF NATURAL DYES PROPERTIES AS PHOTO-SENSITIZER ,FOR DYE SENSITIZED SOLAR CELLS (DSSC), Journal of Electron Devices, Vol. 16, 2012, pp. 1370-1383.

Monishka studied the performance of dye sensitized solar cells as a sensitizer. Various components of a plant such as the flower petals, leaves and bark have been tested as sensitizers. The highest efficiency of 1.70% has been reached by Red Turnip which contains betalain pigment. Monishka found the cause for such low efficiency, is that the contact between betalain and TiO2 would have been low. The structure of the dye also affects the performance i.e., if the structure has a longer R group, this result in the steric hindrance for the dye to form link with the oxide surface of the TiO2 and hence averts the molecule from arranging on the TiO2 film effectively. Hence there is lack of electron transference from the dye molecules to the conduction band of TiO2. The intensity and range of light captivation of the dye also affects the performance. The distance between the dye skeleton and the point connected to the TiO2 surface facilitates electron transfer from the dye molecule to the TiO2 surface which matters for the performance of the cell.

The TiO2 and dye interaction plays an important role towards the efficiency of NDSSCs. In general, natural dyes suffer from low Voc. This can be due to possible ineffective electron/dye cation recombination paths and the acidic dye adsorption environment. In fact H+ are the potential defining ions for TiO2 and that proton adsorption causes a positive shift of the Fermi level of the TiO2, thus limiting the maximum photo voltage that could be provided by the cells. The charge transfer in the TiO2/dye/electrolyte boundary resistance leads to a decrease in Jsc. Thus, introducing a functional group, such as carboxyl group and improving the structure of the natural dye are necessary to increase the efficiency of NDSSC.

Some problem such as dye aggregation on nanocrystalline film yields absorptivity that results in no electron injection. Dye aggregation is a serious matter that happens when compounds fill the free space between the dye molecules, incompletely blocking the physical contact between the iodine solution and TiO2 semiconductor film surface, decreases reaction rate and inhibiting dye aggregation.

[8] Monishka Rita Narayan, Review: Dye sensitized solar cells based on natural photosensitizers, Renewable and Sustainable Energy Reviews 16 (2012) 208- 215.

A.R. Hernández‐Martínez et al.[9] studied dye-sensitized solar cells (DSSC) based on natural dyes take out from five different inexpensive sources .solar cells were fabricated by thin film and a TiO2 mesoporous film on ITO-coated glass; these thin films were characterized by FTIR. The dyes also characterized by using UV-Vis and typical I-V curves were achieved for the cells. The best efficiency was for Punica Granatum with energy conversion efficiency of 1.86%, with a current density Jsc of 3.341 mA/cm2 using an incident irradiation source of 100 mW/cm2 at 25 °C. The Festuca ovina, Hibiscus sabdariffa, Tagetes erecta, Bougainvillea spectabilis and Punica granatum abstracts were analyzed as natural dyes for DSSCs. Higher Fill Factor was obtained due to the existence of the passivation TiO2 layer; this being an important factor in the assessment of the solar cell performance because it is the ratio of the maximum obtainable power to the theoretical power. Another good result was that the combination of betaxanthin and betacyanin yield solar cells with good performance ,this is due to the absorption at different wavelengths of betaxanthin and betacyanin increases the absorption of photons of different energies. It was also investigated that hydroxyl group was found to favor the chemical adsorption of natural dyes on the tio2 surface, improving the electron transfer.

[9] A.R. Hernández-Martínez*1, M. Estevez2 , S. Vargas3, F. Quintanilla4, R. Rodríguez5,Natural Pigment-Based Dye-Sensitized Solar Cells, Journal of Applied Research and Technology, Vol. 10, February 2012,38-47.

M.Oftadeh[10] designed DSSC using sol-gel method to grow as-prepared nanoparticles of anatase TiO2 thin films on ITO glass substrates followed by rapid thermal annealing for working electrode of dye-sensitized solar cells. TiO2 mesoporous tio2 nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the immersion of dye on the TiO2 electrode was analyzed by UV-vis spectroscopy. The consequence of different factors including number of deposited layers, the spacing between two electrodes, sensitization time, and light source power on the performance of DSSC with TiO2 films was studied. By directing numbers of deposited layers, the spacing between two electrodes, sensitization time, and light source power intensity, TiO2-based solar cells with high efficiency was achieved. DSSC with five time spin-coated TiO2 electrode, applying sealant and sensitization time of 24 h in N3 dye under illumination of 100 W cm-2 tungsten lamp resulted the finest power conversion efficiency (g) of 6.61%.The increases in thickness of TiO2 films by growing the numbers of deposited layers can increase adsorption of the N3 dye through TiO2 films to increase the open-circuit voltage (Voc).On the other side short-circuit photocurrents (Jsc) of DSSCs with mono-coated layer of TiO2 films are smaller than those of DSSCs with five-coated layer of TiO2 films. It was due to the fact that the increased width of TiO2 thin films also caused in a decrease in the transmittance of TiO2 thin films. The corresponding results showed that the DSSC with the five time spin-coated TiO2 thin film showed excellent photovoltaic properties.

[10] M. Oftadeh , A. Aghtar , M. Nasr Esfahani,Masoud Salavati-Niasari, Noshin Mir,Fabrication of highly efficient dye-sensitized solar cell and CO2 reduction photocatalyst using TiO2 nanoparticles prepared by spin coating-assisted sol-gel method, J IRAN CHEM SOC DOI 10.1007/s13738-011-0017-8.