Study the Effect of Proton Irradiation for Photovoltaic Cells Characteristics in LEO Orbit

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1 Study the Effect of Proton Irradiation for Photovoltaic Cells Characteristics in LEO Orbit Osama A. Oraby 1*, Mohamed F. El-Kordy 1, Hanaa T. El-Madany 2, Faten H. Fahmy 2, 1 Department of Electronics and Communications, Faculty of Electronic Engineering, Menofia University, Menouf 32951, Egypt 2 Electronics Research Institute, National Research Center Building, Cairo, Egypt * osamaorabi75@yahoo.com Abstract- Protons can present a hazard to both manned spacecraft and to the sensitive components in satellite sub system and instrumentation such as photovoltaic cells. This pair proposed the theoretical I-V characteristic carve for 10 MeV protons with fluence from 108 to 1012 p/cm2 in LEO orbit in space. Also this paper investigates the behavior of the electrical parameters of photovoltaic cells. Furthermore, the development of short circuit current (isc,) and open circuit voltage (Vsc) which gives maximum power at the same equation order (n) repaired to LEO orbit. The mathematical formula far the theoretical I-V characteristic curve from 108 to 1012 p/cm2 and the threshold level are obtained. in addition, the study the electrical parameters (Isc, Voc, Pmax, and F.F) as a function of proton fluence are presented, Also, the comparison between the effect of 10 MeV protons before and after irradiation is studied. Index Terms- Proton effects, Photoltaic cell, LEO orbit, and circuit voltage. I. INTROBUCTION M. Imaizumi [1] proposed a model for high energy and high fluence proton irradiation of Si solar cells which explains the anomalous increase in he and decrease in V oc followed by abrupt decrease of I oc, and cell failure, induced by high fluence proton irradiation. The I sc. increase and the V oc, decrease can be explained by depletion region broadening. The abrupt cell failure can he explained by a decrease in carrier concentration and consequent increase in the resistively of the base layer. The anomalous change in QE can be explained by the generation of a donor-type defect level with proton irradiation and conduction-type conversion. Wang Kong [2] reports the high-energy proton irradiation effects on GaAs/Ge space solar cells. The solar cells were irradiated by protons with energy of 5-20MeV at a Iluence ranging from I x10 9 to 7x10 13 cm -2 and then their electric parameters were measured at AM0. It was shown that the I sc ; V oc and P max, degrade as the fluence increases, respectively, but the degradation rates of 4. i sc, v oc and P max,. decrease as the proton energy increases, and the degradation is relative to proton irradiation-induced defect Ec-0.41 ev in irradiated GaAs/Ge cells. M. Alurralde [3] developed art experimental facility to measure the current voltage characteristic curve of crystalline silicon solar cells, the cells were irradiated with 10 MeV protons and fluenee between 10 8 and p/cm 2. Furthermore, theoretical simulations were performed to establish the relation between the variation of the electrical parameters and the degradation of the lifetime of minority carriers in the base. Also he discussed a proposal of new model of radiation damage for silicon solar cells. In this paper the theoretical 1-V characteristic curve of crystalline silicon solar cells used in LEO orbit in space after irradiation with 10 MeV protons and fluenee between 10 8 and p/cm2 has been studied, Also, the mathematical equation for each case of fluence is obtained. II. PROBLEM FORMULATION The solar cells used in space environment are subjected to bombardment of charged particles of a wide energy range This bombardment introduces defects in the constituent materials of the cells and, consequently, deteriorates its electronic properties. Radiation damage tests, performed under controlled and normalized conditions, allow studying the resistance of the photovoltaic (PV) devices to the space environment and predicting their performance at the end of life (EOL). Therefore, tests are very useful because they allow a proper design, of the modules for a satellite mission. Main sources of radiation at affecting PV modules are protons and electrons trapped by the terrestrial magnetic field and protons. coming from the Sun, the particle flux depending on the orbit of the mission. Other sources of damage are neutrons and 7-rays: these are not relevant in space, but useful for characterization purposes. The radiation damage in satellites at low attitude orbits (lower than 800 km) or in the high altitude ones (5000 km or higher) is mainly produced by protons (close to 90% of damage). Hence, it is important to evaluate the damage production using these particles in the experiments on earth. For satellite applications, the high energy particle radiation in outer space produces defects in semiconductors that cause a reduction in solar cell power output Assessing the expected useful life of the space solar-cell power plant is important [4]. The interested problem is to obtain the theoretical equations of 1-V characteristic curve of silicon solar cell after irradiation with 10 MeV protons and fluenee between 10 8 and p/cm 2. The absolute error and the electrical parameters (short circuit current (I sc ) open circuit voltage (V oc ) Maximum power (P max ), and fill factor (FF) will be studied for each case in details, So, it is too important to study the perfect theoretical characteristic curve by fitting the experimental data and the mathematical equation are obtained which not previously studied before. The obtained electrical parameters under proton irradiation are necessary to improve the operation in LEO orbit in space. 173

2 III. RESULTS AND DISCUSSIONS III. 1. CHARACTERISTIC CURVE DISCUSSIONS The experimental data of the I-V characteristic curve of crystalline silicon solar cells after irradiation with 10 MeV protons and fluence between l0 8 and p/cm 2 is obtained from [3], so curve fitting using Matlab program is applied to obtain the theoretical 1-V characteristic curve. Figure l to Fig. 5 indicate the theoretical I-V characteristic curve of the degradation of crystalline silicon solar cell when irradiated with 10 8 p/cm 2 the equation order(n) varied front 4 to 8 respectively. From these obtained results illustrated in these figures, it is noticed that there is a large error between the theoretical and experimental results for n=4 and 8 respectively. The obtained theoretical results is nearly similar to the experimental results for n=5 and 7 as depicted in Fig. 2 and Fig. 4 respectively. While Fig. 3 shows that the theoretical results is near to the experimental results so, it is the perfect theoretical curve for equation order n=6, Thus the mathematical formulator the optimum 1-V characteristic curve for 10 8 p/cm 2 curve is given as follows: I = V V V V V V (1) Where I is the current of photovoltaic cells, and V is the voltage of photovoltaic cells. Figure.6 to Fig. 9 shows the theoretical I-V characteristic curve of the degradation of crystalline silicon solar cell with 10Mev proton and fluence between 10 9 to p/cm 2 as the equation order n=6, It is seen from obtained results that the optimum I-V characteristic curve occurs for n=6. The mathematical formula for the optimum I-V characteristic curve for 10 9 to p/cm 2 respectively is given as follows: I = V V V V V V (2) I = V V V 4 +10S253V V V (3) I= V V V V V V (4) I = V V V V V V l (5) III. 2. ERROR ANALYSIS AND DISCUSSIONS Figure 10 and 15 indicate the absolute error as a function of the PV output voltage for 10 8 p/cm 2 and 10 9 p/cm 2 respectively. In the case of 10 8 p/cm 2 and the output voltage = 0:384 V, the absolute error is nearly between 0 up to 9 x 10-4 for n=6. While it has a value of 2 x l0-4 up to 2 x 10-3 for n = 5 and 0 up to 5 x 10-3 for n=7. On the other hand, for 10 9 p/cm 2 and V= 0 V: V, the absolute error is between 0 up to 7 x 10-4 for tell. While it has a value of 10-4 up to 2x10-3 for n=5 and 0 up to 5 x 10-4 for n=7. It s seen that the best IV characteristic curve for 10 8 p/cm 2 to p/cm 2 has been occurred for n= 6 as a result of the minimum absolute error achieved at n=6. III. 3. SIMULATION ANALYSIS OF THE ELECTRICAL PARAMETERS Figure 12 to 15 indicates the solar cell electrical parameters, 1 sc, P oc, and F F at different equation orders (n) and fluence between 10 8 and p/cm 2. Its clearly from simulated results that the short circuit current varies with the equation order where noticeable increasing in I sc values occurs until n=6 while I sc reaches to steady state values for higher orders (n=7 to 9). From Fig. 13, it is seen that V oc. decreases smoothly until ie6 but an increase in its value occurs gradually with higher order. Figure. 14 shows that.p max increases rapidly until tell but a clear reaches to steady state for higher order n>6, Figure 15 shows that the fill factor (FE) increases until n=4 and decreases with a value FE>0.7 for equation order n>4, While a noticeable decrease with a value nearly F.F<0.7 for higher order n>6. Thus it is clear that the optimum electrical parameters (values and equation) occurs at equation order n=6 for fluence 10 8 to p/cm 2. The variation of the maximum output power value of silicon solar cells with the output voltage when irradiated from l0 8 to p/cm 2 is indicted in Fig. 16. From this figure it s clear that the output power occurs at l08 p/cm 2 while the lowest value of output power achieved for p/cm 2, III. 4. THE THRESHOLD LEVEL DISCUSSION It is found from Fig. 10 and 12 to 15 that the threshold level occurs for equation order n=6 for different flunces for 10 8 to p/cm 2 because of large losses in the theoretical results occurs for n> THE ELECTRICAL PARAMETERS AND COMPARISON PF 1-V CHARACTERISTICS Figure 17 shows the effect of proton fluence on the electrical parameters. It is noticed that a decrease of the electrical parameters of solar cell with an increase of fluence of proton radiation. The electrical parameters which reach to the highest values at 10 p/cm 2 while the lowest values at p/cm 2. Figure 18 studies the comparison between the theoretical characteristics curve of Si solar cells before and after irradiation with 10 MeV protons with fluence 10 8 to p/cm 2. ft is shown that the degradation of the 1-V characteristic curves decrease with an increase of proton fluence. The best theoretical characteristic curve at normal sun radiation without 10 MeV protons occurs for equation order n=7 while the best theoretical characteristic curve after 10 MeV protons irradiation occurs far n=6. Also the theoretical characteristic curve after irradiation of 10 MeV protons with fluence 10 8 p/cm 2 is the nearest characteristic curve to normal sun radiation. IV. CONCLUSIONS This paper presents a theoretical I-V characteristic curve of the photovoltaic solar cells after irradiation of 10 MeV protons with fluence It 10 8 to p/cm 2 in LEO orbit in space. It is found that the optimum theoretical I-V characteristic curve for each ease of proton radiation for equation order n=6 as a result of the error reaches nearly zero for n=6 and the mathematical equations are obtained, I sc, increases gradually while V oc decreases until n=6 and Power reaches its maximum value at n=6 So the threshold level occurs n=6. The electrical parameters for photovoltaic cell (I sc V oc, and FF) decreases with an increase of proton fluence, From the comparison study between the degradation of theoretical I-V characteristics curve of Si solar cells before arid after irradiation with 10 MeV protons with fluence 10 8 to p/cm 2, the best values for operation in LEO orbit are obtained by decreasing the proton fluence or nearest to the case of normal sun radiation without 10MeV protons. 174

3 REFERENCES [1] M. lmaizumi. M. Yamaguchi, S,J. Taylor, S. Matsuda. 0, Kawasaki, and T. Hisarnatsu, Mechanism for the Anomalous Degradation of Si Solar Cells Induced by High-Energy Proton irradiation. Solar Energy Materials and Solar Cells Journal Vol. 50, pp , 1998, [2] Wang Rong, Quo Zengliang, Zhang Xinghui, and Thai Zuoxu, 5 20 MeV Proton Irradiation Effects. on GaAs/Ge Solar Cells for Space Use, Solar Energy Materials and Solar Cells Journal VoL 77,, pp , [3] M. Alurralde, M. 3. L Tamasi, C. J, Bruno, M. ti. Martinez Bogado, 1. MA. 3. Fernández Vázquez, J. Dunn, Schul T, A. A. Burlon, P. Stoliar, and A. 3. Kreiner, Experimental and Theoretical Radiation Damage Studies on Crystalline Silicon Solar Cell, Solar Energy Materials and Solar Cells Journal, Vol. 82, No.4, pp , May [4] S. M Sm Physics of Semiconductor Devices, John Wiley and Sons, Inc., Chapter 14, PP ,

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