Modeling and Simulation of Efficiency of Five Junction Solar Cell Using MSCS-1D Simulator

The third-generation multijunction solar cell (MJSC) is the most promising solar cell in terms of champion photoconversion efficiency. This advanced photovoltaic solar cell is considered as the future green electricity source to meet the gradually increasing terrestrial energy demand. Usually, MJSC consists of 2 to 6 semiconducting materials. These materials work as the sub-cells or sublayers in a multijunction solar cell. This sub-cell is selected in a fashion so that it can absorb the entire solar spectrum. In this project, the efficiency of a novel solar cell has been investigated. A detailed analysis of each sub-cell has been done using the state-of-the-art MSCS-1D simulation software. The materials of each sub-cell of the solar cell have been selected so that they can efficiently utilize the entire ultraviolet to infrared spectrum. The optoelectronic parameters used in the simulation were collected from the standard references. The photoconversion efficiency of this model is simulated to be 48.29% and 59% for AM1.5G solar radiation under one sun and 500 sun conditions, respectively. These simulation results will assist in realizing the performance of the 5-junction solar cell in practical fabrication.


Introduction
Energy is crucial for the advancement of modern civilization as it powers the technological and industrial processes that drive economic growth and social progress (Zou et al., 2022). Without access to reliable and affordable energy, many of the systems and services that we rely on, such as transportation, communication, healthcare, and manufacturing, would not be able to function at the level they do today. Furthermore, energy is essential for the global economy as it is needed for economic development, infrastructure, and job creation. Since the discovery of fossil fuels around the world, development has become faster to faster for most countries (Chow et al., 2003). Access to energy is also essential for achieving key global sustainable development goals, such as reducing poverty and improving health and education outcomes. But the minable fossils are gradually decreasing with the increase in demand leading to a crisis of this de facto development weapon (Dingbang et al., 2021;. In practical cases, MJSCs are used in extra-terrestrial sophisticated applications such as satellites, space stations, space vehicles, etc. (Komerath & Komerath, 2011). As this type of solar cell belongs to an extremely tough environment, so these solar panels are comprised of very high-quality compound semiconductor materials that make the manufacturing cost significantly higher than the single junction solar panels (Dimroth, 2006). However, due to its higher electricity generation capability from comparatively small areas, researchers are focusing on the development of this advanced PV solar cell for terrestrial application using comparatively low-quality material for cost-effective power production. Multijunction solar cells are promising because they have the ability to convert a broader range of the solar spectrum into electricity, resulting in higher conversion efficiencies. In single-junction solar cells, only a narrow range of the solar spectrum can be converted into electricity, resulting in lower conversion efficiencies. In addition, multijunction solar cells can operate at higher temperatures without a significant loss in efficiency, making them well-suited for use in space and high-temperature terrestrial environments. Fig. 1 presents the multijunction solar cell, panel, and power plant.
III-V concentrator multijunction cells are the most efficient solar cells currently available, making them an attractive option for concentrated photovoltaic (CPV) systems. Their Efficiency rates range from over 40% in recent years to 60% (King et al., 2012). The volume of the material required for cell fabrication is greatly reduced by this CPV technology that lowers the cost of the solar cell. Concentrator multijunction solar cells are made for terrestrial applications . A MJSC is made up of some sub-cell junctions or layers, each of which is designed to absorb and transform a specific amount of solar energy into electricity (Hossain et al., 2016a). Photons of a certain energy level are blocked by each sub-cell layer, while the lower energy photons are passed on to the next layer. The series-connected sub-cells create a higher voltage output compared to the single junction cell. The overall efficiency of the cell can be improved by making use of the highest photovoltaic conversion capacities of each individual sub-cell (Leite et al., 2013). Depending on the bandgap of the material, a multijunction solar cell absorbs different amounts of energy from different parts of the electromagnetic spectrum. When the MJSC exposed to high-energy photons, sub-cells with higher bandgap will produce more voltages per unit area materials with lower bandgaps tend to absorb low-to-high energy photons and yield lower voltages but higher currents. When designing a multijunction solar cell, the selection of the right combination of materials with high and low bandgaps is crucial. In order to reduce the threading dislocations, that lower the open circuit voltage, the adjacent cells must also be latticematched, which can be a challenging task (Patel et al., 2012). Some technologies allow lattice mismatch to a certain extent. Solar cells are an effective renewable energy resource. Unfortunately, higher conversion efficiency and affordability have been the key concerns (Hossain et al., 2016b). With an infinite number of junctions, a multijunction solar cell theoretically offers a maximum of 86.4% conversion efficiency (Yamaguchi and Luque, 1999). In 1997, a four-layered GaInP/GaAs/(not specified)/Ge multijunction solar cell was developed by Sarah Kurtz et al. (King et al., 2002) that could theoretically reach an efficiency of 50%.
Due to the massive potential of generating very high photoconversion efficiency, MJSC already draws concentration to the researchers. It has already been mentioned earlier that up to four-junction MJSCs are found in the literature. Nevertheless, there is scant information about the numerical simulation or practical demonstration of the five-junction MJSCs. Therefore, the article aims to model a novel combination of five-junction solar cell and investigate the photoconversion efficiency using an advanced version of the multijunction solar cell simulator, MSCS-1D. The cell combination incorporated a 1.08 eV bandgap InGaAs material in its third sub-layer to form the new combination GaInP2/GaAs/InGaAs/GaAs0.94-Bi0.06/Ge solar cell. The simulation has been performed to evaluate the key solar cell parameters under the normal atmospheric condition (AM1.5G) as well as concentrating CPV condition. The photoconversion efficiency of the solar cell has been estimated as 48.29% and 51.24%, respectively, for airmass AM1.5G global and AM1.5D direct normal conditions. The simulation procedure is further extended to 500 suns concentrating conditions. As a result, a linear rise in the short-circuit current of around 10% is caused by the high concentration factor.

Materials and Methods
The conversion efficiency of solar panels or the solar cells can be increased significantly by incorporating different bandgap materials as the sub-cell of MJSC that absorb each part of the incident solar spectrum separately. In fact, using this technique, the Shockley-Queisser limit (Markvart, 2022) for the efficiency of single junction cells can be overcome (Khanom et al., 2018). Keeping this principle in mind, the proposed 5-junction solar cell has been investigated. The schematic arrangement of the proposed cell is shown in Fig. 2.
When photons penetrate a material, they are partially absorbed as they travel through the material. If the photon's energy exceeds the bandgap threshold of the semiconductor, it can break chemical bonds and excite an electron from one level to another, creating an imbalance between electrons in two different Modeling and simulation of efficiency of five junction solar cell using MSCS-1D simulator 04(1) 2022 40 bands; thus, creating electrically charged particles called electron-hole pairs. Low-bandgap materials provide greater current density but lower open circuit voltage (V oc ) while high-bandgap materials provide higher V oc but lower short-circuit current density (J sc ). Usually, V oc remains lower compared to the bandgap   (Khanom et al., 2018).
voltage E g of that semiconductor material. For series connected MJSC, the J sc generated from different sub-cells need to match with each other to obtain higher conversion efficiency.
The proposed 5-junction model with a top cell GaInP 2 having a bandgap of 1.9 eV is a high-quality material, capable to absorb the ultraviolet portion of the solar spectrum. For the 2 nd junction, another high-quality material, GaAs with 1.42 eV bandgap has been selected, which is good for absorbing the visible range solar spectrum. From Fig. 3, it has been seen that solar spectrum radiation has peak irradiance in the visible range, thus, GaAs will generate both high current and high voltage. To utilize other portions of the solar spectrum, the In GaAs semiconductor is used as the 3 rd junction, having a bandgap energy of 1.08 eV, which will absorb the near-infrared part. As infrared has the highest range of all other solar spectrums, the combination needs other materials to absorb mid-infrared sections properly. So, a novel compound has been formed from the mixture of GaAs with Bismide (Bi), which makes a bowing of bandgap of GaAs depending on the Bi content (percentage). GaAs 0.94 Bi 0.06 combination creates a bandgap of 0.92 eV, which is appropriate for the concerned multijunction solar cell model. Lastly, the Ge is selected as the bottom layer having a bandgap energy of 0.67eV, which facilitates to absorption rest of the infrared portion. We use light management to split light so that the cell's short circuit current density matches.
The optoelectronic properties for the sub-cells or sublayers of the considered five junction solar cell GaInP 2 /GaAs/InGaAs/GaAs 0.94 Bi 0.06 /Ge has been collected from , is shown in table 1. These parameters have been utilized for simulating each junction using the MSCS-1D tool (Kowsar et al., 2021). The MSCS-1D simulation software is developed based on the modified spectral p-n junction model for MJSCs Kowsar et al., , 2019. The input intensity power is 1000W/m 2 for AM1.5G global radiation. The simulation has been performed for the normal sun condition (1 sun condition) to the concentrating condition (up to 500 sun conditions). The top junction consists of GaInP 2 filled with proper optoelectronic parameters. The dialog box for the first junction of MSCS-1D is shown in Fig. 4.
All the input optoelectronic properties for InGaP 2 have been inserted into the dialog box of MSCS-1D and, after simulating the top junction, the short circuit current density (J sc1 ) and open circuit voltage (V oc1 ) has been determined. Due to higher bandgap energy, InGaP 2 absorbs the ultraviolet to the visible spectrum of Rahman Hasan, Kowsar, Debnath, Rahaman and Palash 43 sunlight irradiance and generated higher J sc1 and V oc1 . Using the similar procedure, otherJ sc and V oc have been simulated for the other four sub-cells. The characteristicscurrent-voltage (J sc vs. V oc ) graph can be generated using the advanced software package. For all five sub-cells of the GaInP 2 /GaAs/InGaAs/GaAs-0.94 Bi 0.06 /Ge, the J sc vs. V oc characteristics curves have been shown in Figure 5. The characteristics curve (J sc vs. V oc ) for each junction has been generating using the MSCS-1D software.

Results and Discussion
The junctions are connected in series so that the same current will flow through the all 5 sub-cells of the solar cell. The lowest current of these junctions will flow through the five-junction solar cell. The rest of the current will be wasted as heat. So, this current mismatching limit the efficiency of a solar cell. Simulation is performed assuming standard test conditions (the input power is 1000W/m 2 at 300K temperature). After the simulation run, the total short circuit current density, open circuit voltage and the efficiency have been obtained. Table 2 presents a brief description of this simulation.
However, the solar cell's input power performance will increase if concentrated solar power is used. The efficiency has been estimated to 48.29% for 1 sun condition, increasing to 59% for 500 sun conditions under the AM1.5G solar radiation spectrum. Input power to the model has been increased by 500x for calculating efficiency under 500 sun conditions.
When sunlight travels through the atmosphere, it is partially scattered. The one thing determining how much direct sunlight reaches the ground is how far it travels before getting to the surface. The ratio of actual travel length and the minimum length is called Air mass. The efficiency of the solar cell also varies with different air mass conditions. Table 3 shows the efficienciesand other performance parameters at different air masses conditions. Previously, researchers proposed a novel GaInP 2 /GaAs/GaAs 0.94 Bi 0.06 /Ge four junction solar cell that had achieved 49.6% efficiency . Adding In GaAs band gap of 1.08eV as the third layer increases the infrared absorption, making the solar cells more powerful and the efficiency has reached at 51.24% for AM 1.5D. We have simulated the efficiency of our proposed solar cell in MSCS-1D, which is based on the modified spectral p-n junction model. In the MSCS-1D, four out of five junction optoelectronic parameters were given built-in. There was no such specification for the third sub-cell, so we had to figure it out for ourselves to run the simulation. Open circuit voltage, fill factor, maximum voltage and current, etc. are only a few of the variables that are associated with short-circuit current density. The mentioned short-circuit current density can be affected by the concentration of light as it enters through a photovoltaic cell by considering the concentrator factor. Thus, as we see from the figure, the efficiency increases proportionally when we increase the concentrated factor. Some modern applications of multijunction solar cells in terrestrial use have been employed with CPV.
In order to escalate the solar cell conversion efficiency, CPV typically uses reflectors (mirrors) and lenses to concentrate strong sunlight onto a particular location Thus, we increase the concentrator factor to see the feasibility of our proposed multijunction solar cell for terrestrial application. As expected, increased efficiency is found using increasing concentration factors. Four different currents have been measured from simulations of the solar cells. In a multijunction solar cell, the lowest current flows through the series connection of sub-cells on the bottom layer. In contrast, surplus currents are drained off by radiative transfer to other layers (Würfel, 2016) (Kurtz et al., 2008).The sum of the open circuit voltages produced by each cell will make up the total open circuit voltage because the five sub-cells are interconnected in series and all of the junctions are reverse biased (Würfel & Würfel, 2016). The added extra layer of InGaAs on the third sub-cell contributes 0.63V open circuit voltage. Adding this voltage to the other four cells increases the overall output to 3.727 V, increasing our solar cell's voltage and efficiency. However, the simulated efficiencies for the 5-junction solar cell are higher, but these are in the upper boundary 55.1% for AM 1.5 G and 71.1% for AM 1.5D condition for the 5-junction ideal MJSCs (Green, 2006), and simulated efficiencies are decent near to the champion 47.1% experimental efficiency that is recently reported in Nature Energy (Geisz et al., 2020). So, the MSCS-1D simulated results and photoconversion efficiencies of the modeled combination could assist the manufacturers in fabricating solar cells efficiently. As the modeled combination consists of three comparatively low-quality materials than GaAs and GaInP 2 , the per-watt cost of the MJSCs surely be reduced, and if CPV technology is used with the MJSC, the efficiency might be increased that trade-off the overall price of the solar cells.

Conclusions
In this work, 1.08eV bandgap InGaAs material has been incorporated as the third sub layer of a new combination five-junction GaInP 2 /GaAs/InGaAs/GaAs 0.94 Bi 0.06 /Ge solar cell. State-of-the-art simulator, MSCS-1D has been used to evaluate the performance of this solar cell. The photoconversion efficiency of the solar cell has been estimated as 48.29% and 51.24%, respectively, for airmass AM1.5G global and AM1.5D direct normal conditions. The newly incorporated InGaAs contributed to 0.63V open-circuit voltage in an overall 3.727V open-circuit voltage, which in turn helps boost the performance of the solar cell for both atmospheric conditions. The MSCS-1D simulated results will offer the manufacturers to fabricate the solar cells efficiently, cost-effectively for the terrestrial,industrial, and residential applications.