mohammadnozari+research+paper

research paper: link to PowerPoint presentation: https://drive.google.com/?authuser=0#folders/0B28kL-Nj2YoHM2VvM29NYnV2UHc Contents: Abstract 1-Introduction 1-1 Early solar cells 1-2 Functions 1-3 Classification 1-4 DSSC 2-Effects on efficiency 2-1 Nano particles 2-2 Novel ligands 2-3 Polymers 2-4 Co-polymers 2-5 Nano wires 2-6 Nitrogen doped TiO 2-7 Al doped TiO 2-8 Ir complexes 3-Conclusion Refrences This is a very brief review on solar cells, DSSC and mechanisms used for improving their efficiency. We are living a world that day by day the demand for energy increases and meanwhile the fossil fuels are being depleted and on top of them global environment preservation concerns necessitates creation of nonpolluting renewable power sources. Some source of energy such as wind, sun light can be used for getting green energy but each have its own pros and cons in making devices for using them. One the high potential candidates is solar cells. According to news posted on Scientific American website energy is one of the 5 big questions that should keep chemist awake at nights. Solar cell is an electrical device which converts energy of light into electricity. Solar cells are also called photovoltaic cell or photocell. When a photo cell is exposed to light, it can produce an electric current. First photovoltaic cell was built by a young French Physicist, Becquerel in 1939[[|1]]. Then the first solar cell was built in 1883 by Charles Fritts. He coated the semiconductor selenium with an extremely thin layer of gold to form the junctions. Of course the efficiency was low and around 1% efficient. Then in 1946 Russel Ohl made the modern solar cell and got the patent for that [[|2]]. Then in 1954 Daryl Chapin,Calvin Souther Fuller and Gerald Pearson while working on semiconductors in Bell Laboratories, they accidentally found that if silicon is doped, it is going to have better functionality and become more sensitive to light [[|3]]. There are some important functions for solar cells and they are as follows: firstly the should be able to absorb light, then they need to have both positive and negative charge carries and finally they need to separate the charge carriers to a conductive external circuit. In one classification they can be divided to Homogenous, Heterogeneous, p-i-n and n-i-p devices. In homogenous devices single material is designed in a way that one side is p-type and the other side is n-type. In Heterogeneous ones there are two different semiconductors as top and bottom layer. And the third type are a there layer sandwiched structures. Solar cells were generated in different production generations: first generation consists of single crystal silicon; second generation consists of amorphous silicon, Polycrystalline silicon, Cadmium telluride, Cadmium telluride and Copper indium gallium diselenide alloy. Third generation consists of Nanocrystal solar cells, Photoelectrochemical cells, Polymer solar cells and Dye sensitized solar cell (DSSC) which are the most efficient among this generation and the fourth generation consist of Hybrid - inorganic crystals within a polymer matrix [[|4], [|5]]. About efficiency we have thermodynamic limits and maximum efficiency for 3 band cell is 63% and for a 4 band cell is 72 %. For obtaining better performance high absorption, light collection and open circuit voltage is necessary. Predictive models and designs rules are necessary for altering device parameters for better efficiency. Relatively low production cost, and ability to work indoors and under subdues light conditions, felixibility in the operating temperature and potential flexibility gets great attention for dye sensitized solar cells [[|6],[|7]]. A dye sensitized solar cell is based on semiconductor which is located between a photo-sensitized anode and an electrolyte. Dye molecules in solar cells absorb light when exposed to light and also function as electron transducing agent for energy conversion. The discovery of dye sensitization of photocurrents on semiconductor electrodes and energy converting cells was the motive of the generating cell for photoelectric power generation. For electrical conductivity in semiconductors by organic dyes either the electrons are in the conduction band or defect electrons which are also here called positive holes are in the valence band. Electro chemical methods are applied for investigating the sensitization effects of semiconductors. Zinc oxide is a usual n-type semiconductor in inorganic chemistry along with hydrocarbon perylene as atypical p-type semiconductor in organic chemistry were investigated by Gerische et al. A charge transfer mechanism and photon injection of carrier by the dye into p and n type semiconductors was shown. The charge transfer happens at the surface of semiconductor and solution [[|8]]. Many research and studies have been done and being done on how it increase the efficiency of DSSCs, Due to availability of the this source of energy –sun- almost all over the world, it can be greatly beneficial if we can make devices with higher efficiencies. Some of them are mentioned in following Cost has always been an important issue against use of most of the new devices and yet people have always tried to find ways for reducing the final cost. The same issue is with dye sensitized solar cells. Photovoltaic devices are widely used for electricity generation but hindered by final cost. Brian O'Regan * & Michael Grätzel created One kind of Photovoltaic cell from medium purity material but with commercially acceptable energy conversion efficiency and low cost. This device is based on transparent film made of nanometer-sized particles of Titanium dioxide, so it has high surface area for semiconductor and with dye characteristicsIt harvests high proportion of light [[|9]]. In charge transfer there are molecules in excited states excited states, and photo electrochemical reactions and the states have been studied by Tributsch and Calvin [[|10]]. There are new types of solar cells known as perovskites solar cells, are organic-inorganic hybrid solar cells, the pervoskite pigment has been used with mesoporous metal oxide films, but the uncontrolled percioiation of perovskite results in big morphological variation, and consequently A wide spread of photovoltaic performance. In these solar cells they use PbI2 into nanoporous titanium dioxide film and then perovskite is added. By using thie method reproductibility of performance increases and it reaches efficiency of approximately 15 per cent [[|11]]. Lots of research are being done on solar cells based on Ruthenium complexes. And one of the new hetro lepticruthenium(II) complex with the name of cis-di(thiocyanato)(4,40-dicarboxylic acid-2,20- bipyridine)(4,40-bis[(triethylene glycolmethylether)(ditolylaminephenyl)ethenyl]-2,20-bipyr-idine) ruthenium(II) shows a high stability, and along with solvent free electrolyte shows no drop of current density [[|12]]. Another heteroleptic polypyridyl ruthenium complex Ru(4,40-bis(5-octylthieno[3,2-b]thiophen-2-yl)-2,20-bipyridine)(4,40-dicarboxyl-2,20-bipyridine)(NCS)2 has been synthesized which has higher molar extinction coefficients and shows a higher a power conversion efficiency [[|13]]. Another type of cyclometalated ruthenium complexes, Ru(C^N^N1)(N^N1^N2)·Cl where N^N1^N2 = 4,4,4-tricarboxy-2,2:6,2-terpyridine and C^N1^N2 = substituted 6-phenyl-2,2-bipyridine has been synthesized and studied for application in dye sensitized solar cells. the effect of different substituents (R = COOH, thiophen-2-yl, F and OCH3) on the ancillary C^N^N! ligand has effects on the photophysical properties and performance of the cyclometalated ruthenium complexes [|[14]]. One of the other things which have been research on is making new dyes which can improve the efficiency of these cells. A Novel 2,6-diphenyl-4H-pyranylidene derivative has been designed. By using this dye both open circuit voltage and photocurrent density show increase in comparison to other dyes [[|15]]. lots of different things are being done for increasing the efficiency of dye sensitized solar cells. One of the tendencies is toward using polymers. Poly(ethylene terephthalate) based electrodes have been used as substitute for glass electrodes, which imporves the flexibility and impact resistance of a dyse sensitized solar cell. Liquid electrolyte are volatile and degrade over time. Recenetly conducting polymers are being used as hole conducting materials [[|16]]. In another step, after using polymers, some groups have tried using copolymers in order to produce even higher efficiencies. It has been reported that they have used diketopyrrolopyrrole (DPP)-based copolymers and pbenzodithiophene [[|17]]. Also other groups have studied on replacing replacing benzodithiophene with naphthodithiophene in diketopyrrolopyrrole-based copolymers and they have reported enhanced solar cell performance [[|18]]. Nowadays in dye sensitized solar cells, typically nanoparticles are used to increase the solar cell efficiency, dye absorbs the photons, and excitons that are rapidly split at the surface of the nanoparticles are created. After splitting, the electrons are injected into the nanoparticles and by doing this the holes move towards the opposite electrode, this is done by a redox species in an electrolyte. The surface of the nanoparticle film and charge collection efficiency of the electrode determine the real efficiency of the cell. One of the other things which can increase the efficiency of dye sensitized solar cells is using zinc oxide nanowire arrays. By using ZnO nanowire (NW) arrays, direct electrical pathways are created which consequently caused rapid collection of carriers which are generated throughout the device [[|19], [|20]]. In other step for increasing the efficiency, nanocrystalline nitrogen-doped titanium dioxide has been used instead of pure titanium dioxide and showed higher photovoltaic performance. (N-doped TiO2) powder was synthesized by a hydrothermal method [[|21]]. The dye-sensitization effects on the ZnO, CdS, and TiO, electrodes in electrochemical photocells have been investigated for different dyes namely anionic, cationic, and zwitterionic. Among these different dyes The most efficient dye-sensitized photocell the one with aluminurndoped porous ZnO sinter electrode. Aluminum doping has contributed to increase of the porosity of the sinter and consequently decrease of the electrical resistance and eventually a higher efficiency. Also investigations show that crystal face influence mainly absorptivity of the electrode surfaces for the sensitizing dyes and not the current quantum [[|22]]. Most the literature in DSSC studies is on ruthenium complexes, yet recenetly some other complexes are being studied for their functions in solar cells. Due to photophysical properties of cyclometallated iridium(III), some studies have been done on sensitizers based on iridium complexes. These complexes have high triplet quantum yields and short radiative lifetime [[|23]]. From the creation of first solar cells till now lots of research and efforts have been done on dye synthesis, isolation and characterization. Most of the research is confined to ruthenium complexes. Within ruthenium complexes, there have been lots of study on how to increase the efficiency such as synthesizing novel ligand with high light harvesting ability. Usage of polymer and copolymer along with using nano particles and nano wires have all contributed to increasing the efficiency. And this research seems a never ending one because of the continues need for energy in all times even future. 1- Williams, R. "Becquerel Photovoltaic Effect in Binary Compounds." //The Journal of Chemical Physics// 32.5 (1960): 1505. 2- Patent US 2402662 A. N.d. 3-“Hall of Fame Inventor Profile: Gerald L. Pearson” National Inventors Hall of Fame. Retrieved 21 Nov 2013 4- //Photovoltaic Energy Conversion: WCPEC-3 : Proceedings of 3rd World Conference on Photovoltaic Energy Conversion : Joint Conference of 13th PV Science & Engineering Conference : 30th IEEE PV Specialists Conference : 18th European PV Secialists Conference : Osaka International Congress Center "Grand Cube", Osaka, Japan, 11-18 May, 2003//. Osaka, Japan: WCPEC-3 Organizing Committee, 2003. 5- Vos, A De. “Detailed balance limit of the efficiency of tandem solar cells” // The Journal of Physics D:Applications // 13. 839 (1980) 6-Nozik, A.J. “Quantum dot solar cells” //The Journal of Physica E:Low-Dimentional systems and Nanostructures// 14.1-2.(2002): 115 7- Vougioukalakis, Georgios C., Athanassios I. Philippopoulos, Thomas Stergiopoulos, and Polycarpos Falaras. "Contributions to the Development of Ruthenium-based Sensitizers for Dye-sensitized Solar Cells." //Coordination Chemistry Reviews// (2010): 2602 8-Gerischer, H. Michel-Beyerle, M. Rebnetrost, F. Tributch, H. “Sensitization of charge injection into semiconductors with large band gap” //Journal of Electrochimica Acta// 13 16(1968):1509 9-O’Regan, B. Gratzel, M.” A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films” //Nature// 353, ( 1991): 737 10-Tributsch, H., and M. Calvin. "Electrochemistry Of Excited Molecules: Photo-Electrochemical Reactions Of Chlorophylls." //Photochemistry and Photobiology// 14.2 (1971): 95-112 11- Burschka, J. Pellet, N. Moon, JS. Humphury-Baker, R. Gao, P. Nazerrruddin, M. Gratzel,M.“Sequential deposition as a route to high-performance perovskite-sensitized solar cells”//Nature// 499(2013):316-319 12- Yum, Jun-Ho, Soo-Jin Moon, Chedarampet S. Karthikeyan, Helga Wietasch, Mukundan Thelakkat, Shaik M. Zakeeruddin, Md.K. Nazeeruddin, and Michael Grätzel. "Heteroleptic Ruthenium Complex Containing Substituted Triphenylamine Hole-transport Unit as Sensitizer for Stable Dye-sensitized Solar Cell." //Nano Energy// (2011): 13-Gao, F. Wang, Y. Jing, Z. Shi, D. Wang, M. et al.”A new heteroleptic ruthenium sensitizer enhances the absorptivity of mesoporous titania film for a high efficiency dye-sensitized solar cell” //Chemical communications// 23(2008):2365-2637 14- Kisserwan H. Kamar, A. Shoker, T. Ghaddar T. “Photophysical properties of new cyclometalated ruthenium complexes and their use in dye sensitized solar cells”//Dalton Transactions// 41 35 (2012) :10643 15- Bolag, A. Nishida, J. Hara, K.”Enhancaned performance od dye-sensitized solar cells with novel 2,6-diphenyl-4H-pyranylidene dyes” //Organic Electronics// 13 3 (2012):425-431 16- Nogeuira, A. Longo, C. ”Polymers in dye sensitized solar cells: overview and perspectives” //Coordination chemistry review// 248 13 (2004):1455-1465 17-Cheng, Y. Yang, S. Hsu, C. “Synthesis of conjugated polyners for organic solar cell applications” //Chemical reviews// 109 11 (2009):5868-923 18-Peng, Q. Huang, Q. Hou, Z. Chang, P. Xu, J. Deng, S. “Enhanced solar cell performance by replacing benzodithiophene with naphthodithiophene in diketopyrrolopyrrole-based copolymers” //Chemical communications// 93 48 (2012):11452-11454 19- Weintraub, B, Yaguang W, and Zhong LWang. "Optical Fiber/Nanowire Hybrid Structures for Efficient Three-Dimensional Dye-Sensitized Solar Cells." //Angewandte Chemie International Edition// (2009): 20- Gupta, N., G. F. Alapatt, R. Podila, R. Singh, and K. F. Poole. "Prospects of Nanostructure-Based Solar Cells for Manufacturing Future Generations of Photovoltaic Modules." //International Journal of Photoenergy// 2009 (2009): 1-14. 21-Liu, W. Feng, Z. Cao, W. "Preparation of large-area dye-sensitized solar cells based on hydrothermally synthesized nitrogen-doped TiO2 powders” //Research on chemical intermediates// 39 4 (2013):1623-1631 22- Matsumura, M. Matsudaira, S. Tsubomura, H. Takata, M. Yanagida, H. “Dye Sensitization and Surface Structures of Semiconductor Electrodes” //Industrial and engineering chemistry products research and development// 19 3 (1980):415-421 23- Baranoff, E. Jung, I. Scopelliti, R. Solari, E. Gratzel, M and Nazeeruddin, M. “Room-temperature combinatorial screening of cyclometallated iridium(III) complexes for a step towards molecular control of colour purity” //Dalton Transactions// 40 13 (2011):6860-6867
 * Dye Sensitized Solar Cells and their efficiency**
 * Abstract:**
 * Inroduction:**
 * 1-1 Early solar cells**
 * 1-2 Functions**
 * 1-3 Classification**
 * 1-4 DSSC**
 * 2-Effects on efficiency**
 * 2-1 Nano particles**
 * 2-2 Novel ligands**
 * 2-3 Polymers**
 * 2-4 Co-polymers**
 * 2-5 Nano wires**
 * 2-6 Nitrogen doped TiO**
 * 2-7 Al doped TiO**
 * 2-8 Ir complexes**
 * 3-Conclusion**
 * References**