STUDY OF THE DEPENDENCE OF THE BASE THICKNESS OF A DUAL-SIDED SENSITIVE SOLAR CELL ON THE IMPURITY CONCENTRATION

ABSTRACT

Prospects for the use of renewable energy sources are increasing day by day. The most efficient way to use renewable energy sources is to use solar energy. The conversion of solar energy into electricity is done through solar panels. There are 2 types of solar panels currently being produced, they are single-sided and double-sided sensitive solar elements. Both types are designed to convert energy from the sun into electricity. In this work, using the Sentaurus TCAD program, it was determined that the input concentration in the base layer of a double-sensing solar cell is directly proportional to the output power. In this case, it was found that the value of the input concentration increases, and it changes more at higher concentrations and less at lower concentrations. The main reason for this is that the input concentration in the base layer is close to the concentration of the metal contact in its back part, and the ohmic resistance is reduced by modeling.

АННОТАЦИЯ

Перспективы использования возобновляемых источников энергии растут с каждым днем. Наиболее эффективным способом использования возобновляемых источников энергии является использование солнечной энергии. Преобразование солнечной энергии в электричество осуществляется с помощью солнечных батарей. В настоящее время производятся 2 типа солнечных панелей: односторонние и двусторонние чувствительные солнечные элементы. Оба типа предназначены для преобразования энергии солнца в электричество. В данной работе с помощью программы Sentaurus TCAD было определено, что входная концентрация в базовом слое солнечного элемента двойного зондирования прямо пропорциональна выходной мощности. При этом было обнаружено, что значение входной концентрации увеличивается, причем оно меняется больше при более высоких концентрациях и меньше при более низких концентрациях. Основная причина этого заключается в том, что входная концентрация в базовом слое близка к концентрации металла контакта в его тыльной части, а омическое сопротивление снижается за счет моделирования.

Keywords: solar panels, dual sensitive, energy, efficiency, Sentaurus TCAD, modeling.

Ключевые слова: солнечные панели, двойная чувствительность, энергия, эффективность, Sentaurus TCAD, моделирование.

Nowadays, the energy demand of all countries is increasing day by day. As the energy reserve decreases in the state sector, its saving or use of renewable energy sources is being implemented [1,2]. Prospects for the use of renewable energy sources are increasing. In particular, Uzbekistan and developed countries are using solar energy, water and wind energy [3,4]. The most efficient way to use renewable energy sources is to use solar energy. The sun has a huge energy reserve and its use is becoming the energy of the future. The conversion of solar energy into electricity is done through solar panels [5]. There are 2 types of solar panels currently being produced, they are single-sided and double-sided sensitive solar elements. Both types are designed to convert solar energy into electricity [6].

Dual sensitive solar panels are being widely manufactured in the industry. These types of solar panels are modern and produce several times more power than single-sided sensitive solar panels [7]. Dual sensitive solar panels work based on the diffuse scattering of sunlight from the back surface. The structure and operation of each solar cell is a complex process [8]. Therefore, we aimed to study the principles of operation of this type of solar cells. Since the sizes of solar elements are small and the processes in them are complicated, we studied them by the method of modeling. The goal of modeling is to simplify calculations, increase accuracy, and eliminate errors in experimental results. The selected program plays an important role in the modeling method. Of course, it is not correct to use any programming languages and programming devices, the program we used is Sentaurus TCAD and Material studio software, which has the ability to model all physical processes and learn as a device.

Since we mainly used Sentaurus TCAD and Material Studio software for modeling, we first created a model of the silicon element in the solar cell. Below are silicon crystal lattices made in Material Studio.

Figure 1. Models of the structure of the silicon crystal in the solar cell

We have modeled the structure of the silicon crystal form, through which we can calculate the distribution of electrons in silicon and their mechanical stability. When using it as a device, we can create the geometric size of the solar element and its parameters in the SDE section of the Sentarus TCAD program. In them, we determine the calculation quantities by the method of meshing. After that, it will be possible to study it as a ready-made device. When learning as a device, using the SDEVISE section, it will be possible to access and apply what external influences can be applied to it, as well as the constants in them. Formulas for calculating the processes occurring in them due to external influence are presented. In particular, we will be able to determine these quantities: light intensity, optical absorption, recombination, mobility of charge carriers and residence time.

Based on the possibilities of this program, we will give the necessary formulas for calculating the electrophysical processes in the silicon material, the basis of the solar cell, and for using it as a device. Due to the p-n junction in the solar cell, an internal electric field is created and separates the electron-hole pair from each other. Then the transfer of charge carriers occurs. The movement of charge carriers creates an electric current. In Sentaurus TCAD, there are mainly 4 models for calculating the transfer of charge carriers: Drey-Diffusion, Thermodynamic, Hydrodynamic and Monte Carlo. In this scientific work, the Drift-Diffusion model given in formula 6 was used to calculate the migration of charge carriers, since the effect of temperature on the solar cell was not taken into account.

                (1)

Here: J_n and J_p are the current density generated by electrons and holes, m_n and m_p are the effective mass of electrons and holes, γ_n and γ_p are quantities determined using the Fermi function, D_n and D_p are the diffusion coefficient of electrons and holes, µ_n and µ_p are the mobility of electrons and holes.

The Masetti formula was used to calculate the mobility of charge carriers. Masetti's empirical formula takes into account the effect of temperature, impurity concentration and phonon scattering on the mobility of charge carriers. Because silicon is a defect semiconductor, radioactive recombination is not taken into account when modeling silicon-only devices. Therefore, only Auger and Shockley-Read-Hall recombination are taken into account. In addition, the role of metal contacts in the quality of solar cells is significant. Due to the fact that the calculation is carried out using numerical methods, electrical boundary conditions should also be included in the model. It was determined that an ohmic transition was formed between the contact and the semiconductor, and the ohmic boundary conditions were used.

                                      (2)

Here: J_m is the current density created by charge carriers in the metal, J_D is the diffusion current density, ϕ is the electrostatic potential, Φ_m is the fermi potential in the metal, Ф₀ is the electrostatic potential in the equilibrium state, n₀ and p₀ are the electron and hole concentrations in the equilibrium state.

Results determined in Sentaurus TCAD software, a single-sided then a dual-sensing solar cell was exposed to AM 1.5g light beam, a single-sided sensitized solar cell was exposed to the frontal part of the light beam, and a double-sensitized solar cell AM1.5g light beam was exposed to the front and back of the solar cell equally vertically. The back surface of the dual-sensitive solar cell was exposed to light through the glass. In this way, we exposed the solar elements to light. A light beam falling on a solar cell is absorbed in its emitter layer, and a p-n junction is formed. The depth of the p-n transition depends on the distance of the light beam. since the light beam falling from the front is close to the p-n junction, and when it is falling from the back, it is farther from the p-n junction, so the energy of the light from the back side means the recombination of charge carriers until it reaches the limit of the p-n junction and creates an additional electric field. The following graphs show the absorption of light from the front and back.  

Figure 2. Dual sensitive solar cell geometric shape

The volt-ampere characteristic of the solar cell was obtained based on this finding. It was found that a solar cell with double-sided illumination is better than a solar cell with single-sided illumination. Below are the volt-ampere characteristics of solar cells in double beam and single beam.   

Figure 3. I-V characteristics of 1 and 2-way sensitive solar cell.

As can be seen from this Fig. 3, the output voltage and short-circuit current of the double-sensing solar cell is 1.5 times the short-circuit current and 1.05 times the output voltage compared to the single-sensing solar cell. These indicators are presented for cases where the width of the base of the solar cell is 8 µm and the thickness of the emitter layer is 1 µm. In this case, the concentration of the emitter layer is phosphorus with 10¹⁷ cm^-3, and boron is included in the base layer with 10¹⁵ cm^-3. This impurity concentration is of great importance and if we increase the values of the impurity concentrations in both layers, it can be seen that the output power in them increases. The Fig. 3 below shows the relationship between the impurity concentration and the thickness of the base layer.

Figure 4. The dependence of the solar cell base thickness on the output power

It can be seen from the graph that the impurity concentration at the base of the double sensitive solar cell increases in direct proportion to the output voltage. In our experiment, we performed calculations by increasing the concentration of boron in the base part from 10¹³ cm^-3 to 10¹⁶ cm^-3. We have also studied the base width for this type of solar cell, where it can be seen that the output power decreases as the base width increases.

In short, it was found that the impurity concentration in the base layer of the double sensitive solar cell is directly proportional to the output power. In this case, it was found that the value of the impurity concentration increases, and it changes more at higher concentrations and less at lower concentrations. The main reason for this is that the impurity concentration in the base layer is close to the concentration of the metal contact in its back part, so the ohmic resistance decreases.

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