Light Trapping Properties of Solar Cells

Light Trapping Properties of Solar Cells Abstract In this paper, we have investigated the light trapping properties of solar cells based on one-dimensional photonic crystal (1DPC) by using finite difference time domain (FDTD) method. Light trapping is essential for thin film solar cells due to the limited absorption in long wavelength range. Here, we used different types of solar cell structures and to explore their photonic ray theories (electric field propagation) and numerical simulations. The one-dimensional thin film solar cell consists of distributed Bragg’s reflector (DBR), Metal back reflector, grating and anti-reflection coating (ARC). The influence of the grating period and depth, the optimal path length has to be increased. These numerical simulations indicate that this combined photonic structure is capable of improving the external quantum efficiency and their absorption. As well as the relative enhancement increased up-to 60% for thin film silicon solar cells. We further to investigate high efficiency of thin fi lm solar cell using different structure. Index terms: Finite difference time domain (FDTD), distributed Bragg’s reflector (DBR), the grating, metal reflector, anti-reflection coating (ARC) and relative enhancement factor. Introduction The scientific community is intensively working to achieve high efficiency thin film solar cells based on silicon. Among the various energy sources, solar energy is well considered to be very promising and achieved wide applications for space and global power generation. The silicon based thin films are cheaper and easy fabrication due to well developed silicon technology. The Silicon based thin films have been the choice as active materials for solar cells, such as crystalline silicon (c-Si), amorphous silicon (a-Si), micro crystalline silicon (ÃŽ ¼c-Si) and so on [1]. The efficiency of silicon thin film solar cell (TFSC) is low due to their weak absorption in longer wavelength range. Thus the light trapping mechanism for thin film silicon solar cell becomes a vital role to improve the conversion efficiency. The crystalline silicon solar cells integrated with the DBR, metal reflector, ARC and grating. Therefore, the incident light is expected to be partially absorbed in the active l ayer of crystalline silicon (c-Si), after the support through the front anti-reflection coating layer (Si3N4) and the back reflector of aluminum (Al) or dielectric (DBR) layers. We are realized that incident light is scattered into the DBR due to the periodic grating and reflected back at the bottom interface. Therefore the way of light trapping in this design is different from usual reflectors based on metals or photonic crystals [2, 3]. In this paper, we will focus on strongly corrugated photonic crystal absorbers made up of a-Si and SiO2 layers are periodically patterned. Finally, the optical presentation of the structure will be indicated by their integrated absorption, the absorbed spectral range between 300-1200nm. This paper deals with the modeling and designing of solar cells using FDTD method. Figure 1 The schematic diagram of the solar cell structure Designing Approach Finite difference time domain (FDTD) method as a sophisticated computational method used to model advanced devices. Figure 1 shows a schematic diagram of solar cell composed of anti-reflection coating (ARC), diffraction grating and photonic crystals also known as distributed Bragg’s reflector. The distributed Bragg’s reflector (DBR) consists of alternate layers of amorphous Si (a-Si) and silicon-di-oxide (SiO2) with their refractive index 3.6 and 1.45 and thickness 56nm, 138nm respectively. The thickness of the each layer is determined by the quarter wave principle (t = ÃŽ »C /4n), where, n-is the refractive index and ÃŽ »C is the center wavelength of photonic band gap. On top of the DBR, diffraction grating is embedded which is made of a-Si and SiO2, with duty cycle (Gdc=0.5ÃŽ ¼m), period (Gp=0.6ÃŽ ¼m) and thickness (Tg=0.1ÃŽ ¼m).The anti-reflection coating (ARC) layer is made of silicon nitrate (Si3N4) and their thickness 0.07ÃŽ ¼m. Result and Discussion The wave propagation designed solar cell is shown in figure 2. We have used commercial available Full WAVE tool supplied by RSoft. We can see light interaction into the device, when one light is made incident on the solar cell. The shorter wavelength is absorbed by the active region while longer wavelength moves toward bottom layer. The grating interaction gives scattering and diffraction of light where as DBR reflects remaining light. This mechanism finally force the light waves into active region. We have designed and analyzed four different structures of solar cells to understand the light trapping mechanism. Figure 2 Schematic diagrams of solar cell structure and their electric field distribution Figure 3 (a) show absorption of solar cells in accordance to wavelength from 300 to 1200nm. To compare the performance of designed devices we have designed a planer solar cell which mainly consists of anti-reflection coating of silicon nitride. The solar cell absorption of DBR and ARC based solar cell is found to be improved than reference solar cell. However, DBR, ARC and GRA based solar cells show distinct absorption as comparisons to cell C1 and C3. We can see added absorption peak in the red and infrared part of solar spectrum for the case of cell 2. Figure 3 Absorption (a) and Quantum efficiency (b) of designed four solar cells Figure 3b shows Quantum efficiency of different types of thin film Silicon solar cells. The solar cell (C2) composed of DBR, ARC and GR Solar cell C2 shows enhanced quantum efficiency then solar cells C1 and C3. The solar cell C2 peaks between 600 and 1160nm range, which indicates the efficient trapping of light. However, reference cell has the less quantum efficiency show sharp as compare to cells C1 and C3. The overall quantum efficiency is found to be increased between the 700 to 1160nm wavelength range. The quantum efficiency clearly exposes the light absorption enhancement of the light trapping structure in certain wavelength range only. The different solar cell structure shows the highest performances and their relative efficiency was achieved up to 60%, it is compared to the reference cell. Figure 4 J-V characteristics for solar cells with different back structures The figure 4 shows the short circuit current versus voltage characteristics of four designed solar cells. The highest short circuit current can be absorbed for cell C2, C3 and C1 respectively. The short circuit current enhancement factors are 21mA/cm2, 53.8mA/cm2 and 60.5mA/cm2. The overall short circuit current of DBR with grating structure got more enhancements (~60%). Table-I shows the short circuit current, open circuit Voltage, relative enhancement factor and cell efficiency of different solar cell structures. Table-1 The comparison of optical characteristics of C-Si solar cell with different back structures with reference structure All the back structures are improved the cell efficiencies as shown in table I. The open circuit voltage (VOC= 0.7V) and the fill factor (FF=84.5%) are similar to all the structures. The back reflectors showing significant enhancement as evidenced by figure 3. Figure 5 The efficiency enhancement of c-Si solar cells with different structures The characteristic of different back reflector with active region and their enhanced efficiency as shown in figure 5. The combination of periodic grating and DBR structure indicates 60% enhancement, while aluminum with grating structure indicates 53.4% enhancement, it is compared to bare silicon or without any reflector on the back surface. It is simulated as a compare to the perfect periodic cell structure. Conclusion In conclusion, we proposed new photonic light trapping structure and the numerical simulations indicate that this combined photonic structure is capable of improving the cell efficiency by more than 55% for thin film silicon solar cell structure. We investigated the mechanism for an efficient light trapping structure for thin film solar cells using FDTD method. At wavelength range between 400 to 1200nm, we got stronger absorption peaks for silicon with metal and grating. The efficiency also increased, it is much more considerable. These results are providing a path to achieve low cost and strong efficiency enhancement for thin film silicon solar cell. Integrated of self assembled alumina and DBR for more light trapping in silicon photo voltaic (PV) devices. The high efficiency solar cell will be greatly more evident for smaller cell thickness and improved their absorption. Further, we will get more cell efficiency using metal nano sphere and texture the grating structure. Reference [1] L.Zhao, Y.H.Zuo, C.L.Zhou, H.L.Li, H.W. Diao and W.J.Wang, A highly efficient light trapping structure for thin film silicon solar cells, Solar energy 84 (2010) 110-115. [2] Krc. J, Zeman, M, Luxembourg, SL Topic, M.Modulated photonic-crystal structures as broad band back reflectors in thin-film solar cells.Applied Physics Letters, (2009), 94(15), 153501-153501-3. [3] Lord RayleighSec. R. S. On the maintenance of vibrations by forces of double frequency, and on the propagation of waves through a medium endowed with a periodic structure, Vol. 24, issue 147, (1887), 145-159. [4] A. Taflove, S.C. Hagness, Computational Electrodynamics, 2nd ed., Artech House, Norwood, MA, 2000. [5] A.F. Oskooi, D.Roundy, M. Ibanescu, P.Bermel, J. D. Joannpoulos, S.G. Johnson, Computer Physics Communications 181 (2010) 687. [6] Xing sheng, steven G. Johnson, Lirong Z. Broderick, Jurgen Michel and Lionel C. Kimerling, Integrated photonic structures for light trapping in thin film Si solar cells, Applied Physics Letters 100 (2012), 111110. [7] L.Zeng, Y.Yi, C.Hong, J.Liu, N.Feng, X.Duan and L.C. Kimerling, Efficiency enhancement in Si solar cells by textured photonic crystal back reflector, Applied Physics Letters 89 (2006), 111111.

Life Of A Teenager Essay

WE TEENS are something our life depends on cell phones, television and lot more. We are more bothered about our fashion and outlook. Our friends play the most important role in our life.A teenager, or teen, is a young person whose age falls within the range from thirteen  through nineteen (13–19). They are called teenagers because their age number ends in â€Å"teen†. Someone aged 18 or 19 is also considered a young adult. Timing of puberty On average, girls begin puberty at ages 10–11; boys at ages 11–12. Girls usually complete puberty by ages 15–17,[2][3][4] while boys usually complete puberty by ages 16-17. The major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average between ages 12–13; for males, it is the first ejaculation, which occurs on average at age 13. In the 21st century, the average age at which children, especially girls, reach puberty is lower compared to the 19th century, when it was 15 for girls and 16 for boys.This can be due to improved nutrition resulting in rapid body growth, increased weight and fat deposition, or eating meat from animals which have been dosed up with oestrogen. â€Å"I memorize the phone numbers of friends whom my parents do not approve of so that their names don’t blink on my mobile phone.† Nothing Like a Friend >> I sometimes fight with my friends, but there’s mutual understanding that we won’t let our parents know. And, usually, we sort out the differences ourselves. >> Some of us get stuck with friends from whom we learn to smoke, drink, splurge, and other vices. For a while, I got entangled with a group of boys and became addicted to video games. >> When I want to attend a party or watch a film, I invent a story, like I am  going to study at a friend’s place. >> Last year one of my classmates was moving to another city. On his last day at school, I gave him `100 so that he could buy himself a present. It was the money my mother gave me to buy a sweater.

Crime and Punishment: Suspense

Suspense begins in Roskolnikov’s thoughts There are times where we find ourselves living in suspense, feeling insecure about what possibly can occur next. So many things that surround us, at times, foreshadow what may happen next. When this happens, we crave to know what is the next event that will arrive. In the book of Crime and Punishment, there are many parts in which the story becomes suspenseful. Well, how does Dostoyevsky achieve and sustain the suspense in his novel? It all starts right when we find out that Roskolnikov creates feelings of hatred towards Alyona Ivanovna, and creates some sort of plan to kill her. Even though in his thoughts laid the plan, he wasn't completely convinced by his own being in actually completing with a crime. But once he was at the bar, where he overheard a conversation about Ivanovna and how she were better off dead, he decided that it was best that he were to do their request. This is before the suspense comes into play. Overhearing the conversations about Alyona Ivanovna persuaded Rokolnikov that it was his destiny to murder her. The more he thought about it, the more he liked the idea. This is where we can see a bit of suspense growing, because as a reader, what can we expect from a man who has never committed a crime such as killing? While Roskolnikov was a bit insecure about his decision in doing murder, he planned to use an ax to murder Alyona Ivanovna. He got his ax, and went his way to her door, waiting the moment where he can take action. It's possible to imagine that in this moment, Roskolnikov probably tensed up in his body, possibly shook out of being nervous, and sweated heavily because he was going to do something he has never done before. The thoughts that lurked in his head of killing another person seemed right to him, because supposedly it was his â€Å"destiny†, but somewhere deep inside of him, he knew the act of murder brought consequences. This is where suspense begins to grow. Roskolnikov appears at her door, waiting for her to be in his presence. She opens the door to find him at her doorstep, and allows him to come in. Roskolnikov offered her something to distract her from seeing him get out his ax, and he was successful. The suspense by now has grown to a whole another level, where we read to find out if Roskolnikov is really capable of killing another person, or not. This part of the book ends with letting us know that he was libertine, and when the chance was presented to him, he got out his ax, and lacerated her until she lied on the floor, dead. Dostoyevsky, the author of Crime and Punishment, was successful in bringing in suspense to this part of the story. He was able to grasp for the reader's attention, in wanting to know more of what Roskolnikov was capable of doing, what would have been his next move, and leaving them in shock when they come to find out what he ends up doing. This had to be one of the times in the book of Crime and Punishment where suspense was presented. Works Cited Dostoyevsky, Fyodor. Crime and Punishment

Solution Focused Therapy And Rational Emotive Therapy

In the three introductory sessions that took place with my client Jean, I practiced Solution-Focused Therapy, Rational Emotive Therapy, and Humanistic Therapy. In this paper I would like to compare and contrast Solution-Focused Therapy and Rational Emotive Therapy as the primary techniques used in the introductory therapy sessions with my client. I have enjoyed practicing all three types of therapy in my three sessions with Jean, but felt that these two were the most prominent to reflect upon in this paper. Through our Introduction to Counseling class and our textbook readings I have learned numerous aspects about the various schools of therapy. I have enjoyed watching Solution-Focused Therapy and Rational Emotive into action†¦show more content†¦This would be unintentionally making it harder to get over the relationship’s ending. There are several questions that the text informs us that we should be mindful of when we are practicing Solution-Focused Brief Therapy. The questions that we should ask include, but are not limited to: What brings you here? What’s already changing? Suppose a miracle happens? What else will be different after the miracle? How is the miracle happening even a little? On a scale from zero to ten (how close are you to 10)? What else can be done? In my introductory counseling sessions I was able to ask my client several of these questions. In my introductory session I asked Jean what brought her to speak with me. Note taking is to be done after the first session unless you are writing down positive things to reinforce back to the client. There is only a break in the first session if needed, anything else would be inappropriate. After my first session I was able to reflect on our notes in preparation for my second session. In my second session with her I asked her what else could be done in regard to making her comfortable to speaking with professionals in the future. As Jean was thinking about goals I also asked her to tell me what else had been changing since the beginning sessions. They questions really helped me to gain perspective through the client’s eyes. In our class readings Solution-Focused Therapy is discussed, â€Å"Solution-focused therapists have foundShow MoreRelatedSolution Focused Therapy And Rational Emotive Therapy2124 Words   |  9 PagesI practiced Solution-Focused Therapy, Rational Emotive Therapy, and Humanistic Therapy. In this paper I would like to compare Solution-Focused Therapy and Rational Emotive Therapy by talking about both individually. I would also like to talk about the differences in these two therapies. I would also like to share how I used these therapies as the primary techniques in the introductory therapy sessions that I had with my client. 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