Effect of Gaussian doping on the performance of a n+-p thin film polycrystalline solar cell under illumination

Abstract

A two-dimensional (2D) analytical model based on the Green’s function method is applied to an n+-p thin film polycrystalline solar cell that allows us to calculate the conversion efficiency. This model considers the effective Gaussian doping profile in the p region in order to improve cell efficiency. The dependence of mobility and lifetime on grain doping is also investigated. This model is implemented through a simulation program in order to optimize conversion efficiency while varying thickness and doping profile in the base region of the cell. Compared with back surface field (BSF) technology, our proposed structure shows a 31% improvement in conversion efficiency for a polycrystalline solar cell. For a monocrystalline solar cell, the BSF technology becomes more efficient.

A new method for improving performances of a polycrystalline solar cell

“…The first model of BSF structure is developed by Del Alamo et al [15] in which the authors considers that the high doped region of back surface p + (BSF) is modelled by a quasisurface that is characterized by the effective surface recombination velocity S eff expressed by: The second model is given by Kolsi et al [7] in the case of Dirac's function doping distribution in which the authors introduce a potential V h in an I-V equation due to the doping drop between p + and p regions. Thus, the new extended I-V equation can be expressed as follows:…”

“…3 shows the variation of conversion efficiency versus doping density in p-region at space charge region limit of the cell N a1 while considering the models [7,15]. The study is done for N p+ =5×10 19 cm -3 , W bsf =0,8μm, W e =0,8μm and W b =30μm.…”

“…Del Alamo model [15] Kolsi model [7] Fig. 3 Conversion efficiency as a function of doping density in p-region at space charge region limit in the case of Kolsi model [7] and Del Alamo model [15] (Np+=5×10 19 cm -3 , Nd=1,3×10 18 cm -3 ,Wbsf=0,8μm, Wb=30μm, d=30μm, Vg=10 6 cm/s) …”

“…Several experimental techniques have been presented in literature to improve the conversion efficiency of the cell such as bulk and surface passivation [3] with ionic implantation or thermal diffusion [4] in order to reduce the recombination at the back and frontal surfaces or preferential doping method [5] to reduce recombination at grain boundary. Other experimental techniques can improve the cell performance by adding a heavily doped region of the side of the back contact of the cell known as the BSF technique [6] or through imposing a Gaussian doping profile in the p-region of the solar cell [7].…”

New Simplified Model of Back Surface Field Polycrystalline Silicon Solar Cells

“…The carrier density is computed for k range from 1 to 10, which has been found to be sufficient to get a good convergence whatever the grain size and the recombination velocity as reported by Kolsi et al [19], while the coefficients ck, sk are determined from the following boundary conditions. These boundary conditions are expressed in terms of the convenient balance of currents, by equating the minority carrier diffusion current and the grain boundary recombination current:…”