Improving Performance of Dye-Sensitized Solar Cells (DSSC)

Improving Performance of Dye-Sensitized Solar Cells (DSSC) Suppression of recombination channels of Dye-sensitized solar cells made of SnO2 using core shell structure of SiO2 extracted from rice husk N. F. Ajward, D.L.N. Jayathilaka, J.C.N. Rajendra and V.P.S.Perera Introduction Dye sensitized solar cells (DSC) are one of the most promising types of solar cells for next generation of solar cell technology that has power conversion efficiency as high as 12% (Nazeeruddin et al., 2011). Compared with conventional silicon photovoltaics, DSSCs offer the cost savings in the materials and a range of solution deposition methods for device manufacture. However, there are still many challenges to be met before DSCs can truly compete with current silicon solar cell technology. Device efficiency, stability and lifetimes and scalable methods for device fabrication are the key issues in this field of research. A lot of work has been done to improve efficiency of DSSCs taking different avenues, which includes increasing the surface area of the metal oxide, developing new dyes with broad absorption spectra, suppressing the recombination channels and introducing light-scattering materials in the film. Utilization of mesoporous film made of nano particles of titania for DSSC is the imperative innovation made by Gratzel and co-workers in 1991 to achieve high efficiencies (Regan B O and Gratzel M., 1991). After that it was realized the possibility to achieving high efficiencies even with other high band gap semiconductors such as SnO2 and ZnO made in nano range (Bergeron et al., 205, Keis et al., 2002). However DSSCs of high efficiencies comparable to that made of TiO2 films has been achieved with other high band gap semiconductor films made in the form of composites (Niinobe et al., 2005]. The improvement is principally accepted as the suppression of recombination of germinated charge carriers due to passivation of trap states and charge carrier confinement. Materials such as Al2O3, MgO, and ZrO2 have been used previously as barrier layers in DSSCs, but no record available for the use of SiO2 for the same purpose (Kay and Grà ¤tzel, 2002). But SiO2 particles have been used to scatter light in TiO2 films of DSScs. In this research work we improved the performance of DSSCs by introducing thin barrier layer of SiO2 surrounding the SnO2 crystallite to prevent recombination of charge carriers in the diffusion assisted transportation. Here the thin barrier of insulating material enhance the lifetime of germinated charge carriers of DSSC so as to improve the efficiency. Methodology Rice hHusks (RH) of BG 300 rice variety was collected and initially washed with tap water to remove soils and dirt. It was further washed with distilled water and dried at 120 ËÅ ¡C. The dried RH will bewas fully burnt to white ash at around 700ËÅ ¡C in a muffle furnace and the Rrice husk Husk ash Ash (RHA) was collected. which is white in colour. Extraction of Silica Aforementioned dried RHA was refluxed with 2M HCl and thoroughly washed with distilled water and dried. 10 g of the sample was stirred in 80 ml of 2.5 N sodium hydroxide solution. It was then boiled in a covered 250 ml Erlenmeyer flask for 3 hours and the solution was filtered using a Whatman No. 41 filter paper. Filtrate was allowed to cool down to room temperature and added 5 N H2SO4 until it reaches pH 2. Then NH4OH was added to the suspension until it reaches pH 8.5 and allowed to be at room temperature for 3.5 hours. The precipitated SiO2 was separated by filtration and thoroughly washed with distilled water. The silica obtained was oven dried at 120 0C for 12 hours and cool down to room temperature. Preparation of SnO2 Particles Tin (ivIV) chloride was dissolved in distilled water to obtain 0.5 M solution and ammonia was added stirring the solution to obtain fine particles of SnO2. The SnO2 particles are thoroughly washed with distilled water to remove chlorine ions. Then the particles are suspended in diluted ammonium solution for stabilization. Preparation of SnO2 and SiO2 core shell structures Tin (IV) Oxide particles were coated with ultra thin layer of silica by the following method. 0.5g of SnO2 particles were weighted and grinded in an agate mortar with 2 ml of ethanol. Then measured volumes of 0.5M sodium silicate which was prepared by dissolving extracted silica in NaOH was added at a time to different SnO2 samples that has been prepared as described above. After that 1 ml of acetic acid was added drop wise to that mixture. Sodium silicate around the SnO2 particles suppose to turn into SiO2 in the process of acidification. Fabrication of DSSC with SiO2/SiO2 composite The paste as prepared was used to coat films on Cconducting Ttin Ooxide (CTO) glass plates by the doctor blade method that cut into the size of 1.5 x 1 cm2. Prior to coating the films on the CTO glass, they were thoroughly cleaned by detergent, distilled water and acetone with ultrasonic agitation. CTO plates coated with SnO2/SiO2 films were dried on a hot plate heated up to 120 à ¯Ã¢â‚¬Å¡Ã‚ °C for 5 minutes. Then the films were sintered at 450 à ¯Ã¢â‚¬Å¡Ã‚ °C in a furnace for 30 minutes. When the films cooled down to the room temperature they were immersed in Ru-bipyridyl N-719 dye solution (0.5 mM in ethanol) for 12 h. After the dye adsorption, films were rinsed with ethanol and sandwich with platinum sputtered conducting glass substrates using clips. The capillary space in between the two plates of cells were filled with electrolyte containing 0.5M potasium iodide, 0.05M iodine in a mixture of acetonitrile and ethylene carbonate 1:4 by volume. Characterization Techniques I-V characteristics of the cells were measured under the illumination of 100 mWcm−2 simulated light source and computer controlled setup consisting of potentiostat/galvanostat. Elemental analysis of RHA was done using Atomic Absorption Spectroscopy. X-ray diffraction (XRD) patterns and SEM images were also obtained for SnO2/SiO2 composite films. Results and discussion According to the literature reports, silica extracted from RH is in naorange with least impurity levels. Elements that present as impurities in RHA of BG 300 rice variety were analyzed with atomic absorption spectroscopy. Percentages of impurities in RHA after burning and refluxing with HCl are given in table 1. Table 1: Percentages of impurities in RHA after burning and after refluxing in HCl. Impurities % in RHA after burning % in RHA after reflux with HCl Calcium 0.926 0.402 Magnesium 0.537 0.198 Manganese Not detected Not detected Ferrous 0.269 0.060 It is inferred from these results that the impurity level of RHA is low and can be reduced further by refluxing with HCl. That is because these impurities present in the RHA as oxides can be removed easily by acid wash. In this study we have investigated the possibility of using SiO2 thin barrier around the SnO2 particles to impede leakage of electrons for recombination processes which is one approach to increase the efficiency of DSSCs. Figure 1(a) shows the measured open-circuit photo-voltage (Voc) and short-circuit photocurrent (Isc) of DSSCs with different SiO2% by weight in the SnO2/SiO2 films. Figure 1: (a) Open-circuit photovoltage (Voc) and short-circuit photocurrent (Isc) of DSSCs with different SiO2 % in SnO2 films (b) Suppression of recombination of injected electrons in the conduction band of SnO2 by SiO2 shell. Initial increment of SiO2 % in the film gradually covers the SnO2 particles as an ultra thin layer and beyond certain limit of SiO2 contributes to the growth of the SiO2 layer around the SnO2 particles increasing the thickness. This is the reason why both the Isc as well as the Voc increase initially with the increment of SiO2 % in the SnO2 films of DSSCs. The increment of Isc and Voc is attributed to the suppression of recombination of injected electrons by the photo excitation of the dye in the conduction band of SnO2 due to the development of ultra thin layer of SiO2 around SnO2 particles (Figure 1b). The highest photocurrent of DSSCs with the addition of 2.5 % of SiO2 may have been achieved due to the perfect coverage of SnO2 particles with ultra thin layer of SiO2. But Voc continues to increase further up to 4% of SiO2 in SnO2 films. It is noticeable that the decrement of Voc afterward is not significant as in Isc after reaching the maximum. Anyway further increment of the thick ness of the ultra thin layer of SiO2 happens to decrease both Isc and Voc. The amount of dye adsorbed on the semiconductor film is also a detrimental factor on the performance of DSSCs. We have noticed that the dye absorbed on SnO2 films decreased with the increment of SiO2%. To quantitatively analyze it, we have desorbed the dye adsorbed on SnO2 films with different SiO2 %. This was done by allowing the films to adsorb dye for determined period and completely desorbing the dye by immersing the dye adsorbed SnO2 films in known volume of 0.5 M KOH solution. The concentration of the dye in the KOH solution was estimated spectroscopically at the wave length of 550 nm. Figure 2 given bellow shows the deviation of dye adsorbed on SnO2 films for different SiO2 %. Figure: 2 (a) Variation of dye adsorbed on SnO2 films for different SiO2 % and (b) structure of the N-719 dye. It is evident from the Figure 2 that the dye adsorption on SnO2 films decrease with the increment of SiO2 %. This may affect adversely on photocurrent of DSSCs. Although dye aggregations on semiconductor films also results to decrease photocurrent there should be sufficient amount of dye adsorbed on SnO2 crystallites for efficient operation of DSSCs. The decrement of Isc at higher SiO2 percentages is main consequence of low dye adsorption on SnO2 films. The adsorption of dye on SnO2 films decrease with the increment of SiO2 % because of the acidity of SiO2 which prevent chelation of N-719 dye on SnO2 films by the carboxylic groups. XRD and SEM analysis was also carried out to characterize the SiO2 ultra thin layer coated on SnO2 particles. Figure 3 shows the SEM of SnO2 film with 4.5% of SiO2. The resolution of the SEM images was not sufficient to identify the SiO2 thin layer. But it can be seen that the SnO2 particles are distributed in wide range of particle sizes which also affect adversely on the performance of DSSCs. The XRD pattern of the SnO2 film with 4.5 % of SiO2 is given in Figure 3(b). There was no any peaks appeared for SiO2 in the XRD pattern of the SnO2 films as well. The insertion in the Figure 3(b) is the XRD obtain for SiO2 powder obtained by acidification of Na2SiO3 with acetic acid and sintering at 450  °C for 30 minutes. It is found to be in amorphous form and most probably the SiO2 around the SnO2 is also amorphous. Because of the amorphous nature of SiO2 and low percentage might produce significant peaks for SiO2 in the XRD pattern. Figure 3 (a) SEM image of SnO2 film with 4.5% of SiO2 (b) XRD pattern of the SnO2 film with 4.5 % of SiO2. Insertion is the XRD obtain only for SiO2 powder. Conclusions The silica extracted from rice husk is with low impurity levels suitable for coating ultra thin layers of SiO2 arround SnO2 to fabricate DSSCs. Deposition of ultra thin layer of SiO2 on SnO2 particles improved the performance of DSSCs. The reason for decrement of cell performance with higher percentages of SiO2 is not only due to the barrier thickness, but also due to the low dye adsorption. It was observed by the SEM images that the particle size of SnO2 is widely diverse because of particle aggregation. It is recommended to use uniform size of SnO2 particles for better performance of DSSCs. some chemical treatment also required to enhance the adsorption of dye on SiO2 ultra thin layer on SnO2 particles. References 1. Bergeron B.V. , Marton A., Gerko Oskam G., and Meyer G.J.; (2005) Dye-Sensitized SnO2 Electrodes with Iodide and Pseudohalide Redox Mediators; J. Phys. Chem. B, , 109 (2), 937–943. 2. Kay A. and Grà ¤tzel M.; (2002) Dye-Sensitized Core−Shell Nanocrystals:à ¢Ã¢â€š ¬Ã¢â‚¬ ° Improved Efficiency of Mesoporous Tin Oxide Electrodes Coated with a Thin Layer of an Insulating Oxide; Chem. Mater., 14 (7), 2930–2935. 3. Keis K., Bauer C., Boschloo G., Hagfeldt A., Westermark K., Rensmo H., Siegbahn H.; (2002) Nanostructured ZnO electrodes for dye-sensitized solar cell applications; Journal of Photochemistry and Photobiology A: Chemistry, 148, issue 1–3, 57–64. 4. Nazeeruddin M. K., Baranoff E, Gratzel M., (2011) Dye-sensitized solar cells: A brief overview; Solar Energy 85 1172–1178. 5. Niinobe D. , Makari Y., Kitamura T., Wada Y., and Yanagida; S.; (2005) Origin of Enhancement in Open-Circuit Voltage by Adding ZnO to Nanocrystalline SnO2 in Dye-Sensitized Solar Cells; J. Phys. Chem. B, , 109 (38), 17892–17900. 6. Regan B O and Gratzel M; (1991) A low cost high efficient solar cell based on dye sensitized colloidal TiO2 films; Nature 353 737.

A Clean Well-Lighted Place

A Clean Well-Lighted Place is among one of the many literary masterpieces of acclaimed writer, Ernest Hemingway. It is very characteristic of his writing style that contains deeper undertones than how they are presented. It suggests more complex meanings and perceptions about universal subjects like life and religion and may possibly be reflective of Hemingway's life in particular.This is a story about three characters who were in a cafe and have exchanged a few dialogues. The simplicity of how the story was written and it's short length definitely stirs the emotions of the readers. It cultivates interest on the concealed meanings in the different exchanges and manner of the characters. It may seem somewhat vague and does not elaborate on the details making it all the more enticing as much as it is frustrating.Take for example, details which concerns the old customer. Not much detail with regards to his act of committing suicide was included. Information on the reasons why he lost hi s wife was also omitted which might have been very useful in interpreting the man's reasons for doing an act that would end his life. This deliberate attempt by the author to conceal some points in the story keeps the reader in question about the authorial intention behind this presentation.In the analysis of the story's writing style, one can assume that the authorial purpose in his work is to amplify a certain idea that will contribute to the fullness of the story's theme. It aims to invite a sense of introspection that is important in understanding the concept of the story as well as looking within to futher realize the truthfulness of the story's relevance when applied to real life.Though the characters are only minimal, they are very much representative of the group that the author would like to emphasize. The old man as well as the older waiter represents the older generation and the young waiter is characteristic of the young generation. Both the waiters are having a conversa tion referring to the old man that is their customer.They are both referring to something that everyone will have to undergo — old age. Their different views and thoughts about the old man is different and contrasting, like the idea that the old waiter presented. He says that a wife would do the old man good which the younger waiter disagrees to. The old waiter also shows compassion and patience to the old man and even arguing with the young waiter about letting the old man extend.The young waiter reacts as would young persons usually do, be irritable and make rude remarks about the old man which they do not realize will be an eventuality for them in the future. The older waiter on the other hand, probably realizing that he is aged as well, exhibits a more emphatic manner when it comes to the old man. As the story develops, the characters also develop in a sense that contributes to the theme of the story.The old waiter soon evolves into a character very similar to the old man . The turning point of his character was when he said the following lines, â€Å"Each night I am reluctant to close up because there may be some one who needs the cafà ©.†This act of generosity simply shows that he can relate to all those who need refuge during the night and those who need a clean and well-lit place to stay. This is also evident in his act to mask his real problem by making himself believe that he has insomnia which a lot of people suffer from. He intends to make it seem that he is suffering from something that is common instead of suffering from a deeper ailment of the heart and the emotions.

The Number One Article on Dreams Essay Topics

The Number One Article on Dreams Essay Topics If you get a strong desire to accomplish your dreams, then it will boosts your self-confidence and will assist you in solving a number of the worst stages of your life. Surrounding yourself with those who believe in your dreams and motivate you to work hard to attain the exact same is a great way to remain motivated. To me, they are the most important part of living. This dream is supposed to occur when you're experiencing low self-esteem or too little self-confidence, or whenever you're going through a present situation in which you truly feel powerless! While it is necessary to have high standards and lofty goals they ought to be realistic and doable to prevent disappointment. Our country was once famous for its rich cultural heritage that is all robbed now. The crime rate in the nation is at an all-time rise and so are various different troubles. There are many problems in the nation like poverty, illiteracy and casteism to mention a couple. New Questions About Dreams Essay Topics Writing an essay on Dreams may be an overwhelming endeavor to take on. Fortunately, Buckingham and the remainder of the group provedn't dissuaded by any first reservations McVie had about Dreams. Dreams are our guide all we have to do is follow. Dreaming for big goals are extremely important and they are able to even be dreams that change the duration of your whole life. Dreaming is similar to climbing a mountain. Dreams are occasionally confusing and surprising. They may be real or imaginary. They may simply be the means to unbury hidden emotions that you hadn't dealt with. Up in Arms About Dreams Essay Topics? These dreams usually happen when you're extremely concerned about the approaching day and you wish to be fully ready to face the challenge. Cancer is still a significant disease in many nations. Sleep isn't entirely quiescent. Brain is a rather interesting and distinctive issue to study about. Let's make it even more interesting. Dream is what you would like to do for your future. Winter Dreams signifies more than the simple comprehension of the title. Dreams are so atypical that scientists believe they have a critical intent. With enough research, you can end up discovering a link between them both. At this point you have five unique topics to compose a paper on. Sensory details are the trick to engaging with the audience an d it is imperative to have as many as are relevant. Language is, clearly, important but one must go deeper and make certain that readers feel emotionally connected in addition to appreciate the subject's significance. Dream has lots of meaning and types. Introduction Dreams play a critical part in shaping our future. Regardless of what's happening, I write. Just be certain that it is something which you require, not just something which you desire in the brief term. You should have your reasons, and our primary concern is that you wind up getting an excellent grade. Commonly, individuals daydream when they're alone, relaxed, or inside a boring place or subject, or only going to fall asleep. Choosing Dreams Essay Topics Is Simple Thus, it's possible that melatonin does indeed have a positive influence on sleep, although the benefits may change from individual to individual. You do not have to be worried that you've got wet the bed. In a wet dream, there isn't any touch of the penis that results in the stimulation of orgasm and so semen coming out. You will feel like you're hyper-aware throughout sleep, resulting in very little deep sleep and the majority of light sleep or REM sleep. Figure out what are the considerable significance of the customary dream. Keep in mind is among the older architectures, and artifacts are somewhat more pronounced. You don't post your worst day on social networking and straight away get plenty of thumbs up. TV has become the most engaging medium. The Dreams Essay Topics Game Those individuals, who don't have any cherished dreams, despite the fact that they will never be in a position to make it come true, appear to be deprived of something special, just enjoy those folks, who lack a feeling of humor. Some individuals are often quite talkative and they frequently like to tell about their very own life. After a day or two, recall needs to be easier. There's no accurate answer as to the reason why people dream. Still it didn't break the friendship. To dream that you're murdered suggests that some important and significant relationship was severed. After discovering our website, you will no longer will need to bother friends and family with these kinds of requests. If you are in possession of a good friend that you may confide in, speak to them.

Quotes About What a 50th Birthday Means

If you are turning fifty, my hearty congratulations on the golden jubilee celebrations! Let the wine pour and the music roll, as you watch your life unfurl. Now that you are free of several responsibilities, you can sit back and enjoy the fruits of your labor. Here are some wonderful 50th birthday quotes to keep you rocking for the next decade! Victor Hugo: Forty is the old age of youth; fifty is the youth of old age.TS Eliot: The years between fifty and seventy are the hardest. You are always being asked to do things, and yet you are not decrepit enough to turn them down.Sophie Tucker: From birth to age eighteen, a girl needs good parents. From eighteen to thirty-five, she needs good looks. From thirty-five to fifty-five, she needs a good personality. From fifty-five on she needs good cash.Coco Chanel: Nature gives you the face you have at twenty, but its up to you to merit the face you have at fifty.Elizabeth Cady Stanton: The heyday of womans life is the shady side of fifty!Bob Geldof: I do think I feel it but you dont think you are cause at a certain time you are no age but you dont think you are anything. You feel the life you have lived. I feel that. Its been a long fifty years.Dawn Wells: Just because a woman is over fifty does not mean she no longer has anything to offer. If anything, we have so much more to offer! We have lived life, we get better with age. I do my best work now in my 60s. Sure, I could retire; but what would I do? Play Bingo? I think not!Cindy Crawford: The face you have at age twenty-five is the face God gave you, but the face you have after fifty is the face you earned.