Mathematical Modeling of Silicon Doping by Neutron Transmutation Doping Method for High Efficient Solar Cells
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Mathematical Modeling of Silicon Doping by Neutron Transmutation Doping Method for High Efficient Solar Cells Valery L. Dshkhunyan1, Alexander A. Dyakov2, Sergey M. Karabanov3, Andrey V. Kozlov2, Dmitry V. Markov2and Masahiro Hoshino4 1 Solar Consult Ltd., 51 V Novaya St., Ryazan 390027, Russia 2 Institute of Nuclear Materials JSC, P.O. Box 29 Zarechny, Sverdlovsk region 624250, Russia 3 Ryazan State Radio Engineering University, 59/1 Gagarina St., Ryazan 390005, Russia 4 Japan Semiconductor Engineering Consulting, Buririansu Minami-urawa, 101 Daitakudo 27881-1, Saitama-city, Saitama, Japan ABSTRACT It is known that n-Si solar cells have higher efficiency than p-Si solar cells. One of the problems connected with n-Si application for solar cell production is the difficulty of using Czochralski method for growing n-Si ingots, uniform in structure. The present paper examines the possibility of production of n-Si ingots, uniform in resistance, by neutron transmutation doping (NTD) for photovoltaics using the mathematical modeling method. The provided calculation data are obtained by MCU-RFFI/A accounting code with DLC/MCUDAT-1.0 constant library developed by «Kurchatov Institute» Russian Research Center. The MCU accounting code is used for solution of the neutron-transport equation by Monte-Carlo procedure on the basis of estimated nuclear data for arbitrary three-dimensional geometry systems. The present paper provides the estimation of uniformity of neutron-flux density along the ingot length and radius; dependence of silicon resistance on duration of irradiation. These studies established the neutron flux density distribution along the ingot length and radius; regularities of silicon resistance changes on duration and intensity of irradiation. INTRODUCTION The share of silicon solar cells in global production is more than 80%. Currently p-Si is the basic material for solar cells. It is known that n-Si solar cells have a number of significant advantages: n-Si is less sensitive to impurities (e.g., Fe) and defects that results in higher charge carrier lifetime and therefore, in higher conversion efficiency [1,2]; n-Si is more stable and less subjected to light-induced degradation than boron-doped p-Si [3]; n-Si, used in solar cells based on a-Si:H/c-Si heterostructures, provides higher conversion efficiency [4]. However, it is known that at production of large diameter (150 mm) n-Si monocrystals by Czochralski method and zone melting, the problem of providing the ingot doping uniformity along its length and cross section [5]. This problem can be solved by using neutron transmutation doping (NTD) of silicon by phosphorus [6,7]. The NTD method is based on a nuclear reaction: 30Si isotope absorbing neutron is changing to 31Si which changes to 31P: 30 Si(n, ) 31Si 31 P . As a result, n-Si with highly-homogeneous distribution of phosphorus dopant along the ingot volume is obtained.
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