Impact of Polycrystalline Crystal Size and the Capture Effect at the Contact Surface of Two Crystals on the Effect of P-layer Dopant on Some Electrical Parameters

Silicon ingots can be crystallized using a variety of processes. These lead to different qualities of crystal, and therefore of solar cell, depending on whether the silicon obtained is polycrystalline, i.e. made up of a multitude of crystals of varying size and orientation, or monocrystalline, i.e. formed from a single crystal. Like crystallization, doping is one of the steps in the silicon manufacturing process. Studying the doping level of a solar cell is crucial, as it has a direct influence on its performance, particularly its ability to convert sunlight into electricity. Doping, which consists in introducing impurities into silicon, modifies the electrical properties of the material and, consequently, the characteristics of the solar cell. The aim of this study is to assess the impact of polycrystalline crystal size and the capture effect at the contact surface of two crystals on the effect of p-layer dopant on effective diffusion length, diode current, short-circuit current and open-circuit voltage. Using the continuity equation with generation-recombination phenomena, this study found mathematical expressions for the fundamental electrical parameters needed to characterize solar cells. These mathematical expressions relate the effective diffusion length, diode current and electrical parameters such as short-circuit current and open-circuit voltage to the p-layer doping rate, crystal dimensions and carrier loss rate at the interfaces, respectively. Then, using Mathcad software, we simulated the impact of crystal size and the effect of captures at crystal interfaces on the influence of p-layer doping rate on effective diffusion length, diode current and electrical parameters such as Jsc and Voc. The results obtained from this analysis reveal that: For low values of p-layer doping rate and crystal size, the short-circuit current and effective diffusion length decrease less with low p-layer doping rates. On the other hand, for p-layer doping rates higher than 10¹⁷cm⁻³, the effective diffusion length and short-circuit current intensity decrease, but this decrease is faster when the crystal size is smaller. Diode current and open-circuit voltage increase with p-layer doping rate and crystal size. Growth is greatest when the p-layer doping rate is greater than 10¹⁷cm⁻³ for diode current. The results of this study make it possible to design more efficient solar cells for polycrystalline silicon photovoltaic applications by keeping the doping rate at or below 10¹⁷ cm⁻³.