Teoretičeskaâ i prikladnaâ nauka Theoretical & Applied Science 07 (27) 2015 International Scientific Journal Theoretical & Applied Science Editor-in Chief: Hirsch index: Alexandr Shevtsov (KZ) h Index RISC = 1 (56) The Editorial Board: Prof. Vladimir Kestelman (USA) h Index Scopus = 2 (30) Prof. Arne Jönsson (Sweden) h Index Scopus = 3 (18) Prof. Sagat Zhunisbekov (KZ) Founder : International Academy of Theoretical & Applied Sciences Published since 2013 year. Issued Monthly. International scientific journal «Theoretical & Applied Science», registered in France, and indexed more than 34 international scientific bases. Address of editorial offices: 080000, KZ, Taraz, Djambyl street, 128. Phone: +777727-606-81 E-mail: [email protected] http://T-Science.org Impact Factor ISI = 0.829 ISSN 2308-4944 based on International Citation Report (ICR) 0 7 © Сollective of Authors 9 772308 494157 © «Theoretical & Applied Science» International Scientific Journal Theoretical & Applied Science Materials of the International Scientific Practical Conference Intelligent technologies 30.07.2015 Marseille, France The scientific Journal is published monthly 30 number, according to the results of scientific and practical conferences held in different countries and cities. 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Impact Factor ISI = 0.829 based on International Citation Report (ICR) ISSN 2308-4944 0 7 9 772308 494157 ISRA (India) = 1.344 SIS (USA) = 0.912 ICV (Poland) = 6.630 ISI (Dubai, UAE) = 0.829 РИНЦ (Russia) = 0.179 Impact Factor: GIF (Australia) = 0.356 ESJI (KZ) = 1.042 JIF = 1.500 SJIF (Morocco) = 2.031 SOI: 1.1/TAS DOI: 10.15863/TAS Nfally Dieme Laboratory of Semiconductors and Solar Energy, International Scientific Journal Department of Physics, Theoretical & Applied Science Faculty of Science and Technology, Cheikh Anta DiopUniversity, p-ISSN: 2308-4944 (print) e-ISSN: 2409-0085 (online) Dakar, Senegal [email protected] [email protected] Year: 2015 Issue: 07 Volume: 27 Moustapha Sane LSSE, DP, FST, Cheikh Anta DiopUniversity, Published: 30.07.2015 http://T-Science.org Dakar, Senegal [email protected] SECTION 6. Metallurgy and energy. Idrissa Fabe Barro LSSE, DP, FST, Cheikh Anta DiopUniversity, Dakar, Senegal [email protected] PHOTOCURRENT AND PHOTOVOLTAGE UNDER INFLUENCE OF THE SOLAR CELL THICKNESS Abstract: A theoretical study of a parallel vertical junction silicon solar cell under a multi-spectral illumination in static regime has been done under impact of the thickness of this solar cell. Based on the diffusion- recombination equation, the expression of excess minority carrier density in the base was established according to the thickness. Photocurrent density and photovoltage are then deduced. The objective of this work is to show the effects of solar cell thickness on these electrical parameters. Key words: photocurrent density, photovoltage, thickness, Vertical junction. Language: English Citation: Dieme N, Sane M, Barro IF (2015) PHOTOCURRENT AND PHOTOVOLTAGE UNDER INFLUENCE OF THE SOLAR CELL THICKNESS. ISJ Theoretical & Applied Science 07 (27): 1-6. Soi: http://s-o-i.org/1.1/TAS-07-27-1 Doi: http://dx.doi.org/10.15863/TAS.2015.07.27.1 1. Introduction rays simultaneously touch the base, the junction and The vertical junction solar cell is manufactured the emitter. Each base and emitter is bordered by an by an alternative junction base -emitter-base-emitter. aluminum collector as shown in the following Both sides have the same thickness [1]. The incident figure1. Figure 1 - Parallel vertical junction solar cell. ISPC Intelligent technologies, Marseille, France 1 ISRA (India) = 1.344 SIS (USA) = 0.912 ICV (Poland) = 6.630 ISI (Dubai, UAE) = 0.829 РИНЦ (Russia) = 0.179 Impact Factor: GIF (Australia) = 0.356 ESJI (KZ) = 1.042 JIF = 1.500 SJIF (Morocco) = 2.031 The bases are interconnected by a connecting wire to comment on the impact on the performance of solar define the positive electrode and the emitters are cells. connected together to form the negative electrode. The aim of this work is to investigate the influence of 2. Mathematical study The thickness of the solar cell on electrical 2.1. Hypotheses parameters such as photocurrent and photovoltage. We assume that the following hypotheses are Knowing the evolution of these two quantities based satisfied. on the thickness is a good indicator for us to The solar cell is illuminated along the z axis. Figure 2 - Base of parallel vertical junction solar cell (thickness: H; width:W =0,03cm). The contribution of the emitter is neglected. Illumination is made with polychromatic light K in steady state, and is considered to be uniform D . .T (2) on the z = 0 plane. q There is no electric field without space charge with q as the elementary charge, k the Boltzmann regions. constant and T temperature. G(z) is the carrier generation rate at the depth z in the base and can be written as 2.2. Density of minority charge carriers biz When the solar cell is illuminated, there are G(z) aie (3) simultaneously three major phenomena that happen: generation, diffusion and recombination. ai and bi are obtained from the tabulated values These phenomena are described by the of AM1.5 solar illumination spectrum and the diffusion-recombination equation obtained with: dependence of the absorption coefficient of silicon with illumination wavelength. n(x), L, , and μ are respectively the density of 2n(x) n(x) G(z) (1) the excess minority carriers, the diffusion length, x2 L2 D lifetime and mobility. D is the diffusion constant and is related to the The solution to the equation (1) is: operating temperature through the relation [2], [3] x x ai 2 biz n(x) Asinh( ) Bcosh( ) L e (4) L L D Coefficients A and B are determined through at the junction (x=0): the following boundary conditions: ISPC Intelligent technologies, Marseille, France 2 ISRA (India) = 1.344 SIS (USA) = 0.912 ICV (Poland) = 6.630 ISI (Dubai, UAE) = 0.829 РИНЦ (Russia) = 0.179 Impact Factor: GIF (Australia) = 0.356 ESJI (KZ) = 1.042 JIF = 1.500 SJIF (Morocco) = 2.031 S n(x) f n(0) n(0) (5) V k.T ln N . 1 (8) x D ph B 2 x0 q ni This boundary condition introduces a parameter with Sf which is called recombination velocity at the 3 junction; Sf determines the flow of the charge 2 Eg carriers through the junction and is directly related to ni An.T .exp( ) (9) the operating point of the solar cell. The higher Sf is, 2KT the higher the current density will be. ni refers to the intrinsic concentration of in the middle of the base (x=W/2) [5]: minority carriers in the base, An is a specific constant of the material 16 ( A n =3.87x10 for silicon) N is the base doping concentration in impurity n(x) B 0 (6) atoms w x x Eg is the energy gap; it is given by [3]; [4]: 2 Equation 8 illustrates the fact that excess carrier concentration reaches its maximum value in the a.T 2 middle of the base due to the presence of junction on Eg Eg 0 (10) b T both sides of the base along x axis (figure 1). -4 -2 (Eg0=1.170 eV; a=4.9 10 eV.K ; b=655K for silicon) 2.3. Photocurrent density The photocurrent Jph is obtained from the following relation given that there is no drift current 3. Results and discussion [5]: In this section of our work, we present the n(x) results obtained from simulations. J 2qD (7) ph x x0 3.1. Photocurrent density The figure3 and Figure4 show the impact of the solar cell thickness on the photocurrent density. 2.4. Photo-voltage The photo-voltage derives from the Boltzmann relation [6]: Figure 3 - Photocurrent density versus junction recombination velocity. T=300K ISPC Intelligent technologies, Marseille, France 3 ISRA (India) = 1.344 SIS (USA) = 0.912 ICV (Poland) = 6.630 ISI (Dubai, UAE) = 0.829 РИНЦ (Russia) = 0.179 Impact Factor: GIF (Australia) = 0.356 ESJI (KZ) = 1.042 JIF = 1.500 SJIF (Morocco) = 2.031 Figure 4 - Photocurrent density versus temperature Sf=105cm. La figure3 shows the evolution of the density. This same Remark is noticed in the figure5 photocurrent density versus junction recombination that shows the profile of the photocurrent density velocity for various values of solar cell thickness. It versus temperature for various values of the solar cell can be seen that the photocurrent increase with the thickness. In this figure we note that photocurrent junction recombination velocity. The recombination density increases as operating temperature increase velocity at the junction reflects the stream of carriers [8], [9]. crossing the junction [7]. For higher Sf, the carrier flow through the junction increases so that the 3.2. Photovoltage generated photocurrent also increases: the solar cell The figure5 and Figure6 show the impact of the operates near short circuit [10]. solar cell thickness on the photocurrent density. It can also be seen that the increase in the solar cell thickness causes a decrease in the photocurrent Figure 5 - Photovoltage versus junction recombination velocity T=300K.