Application of Photovoltaic (PV) Cell and Limited Factor

. With the concept of carbon neutrality and carbon emissions peak, the Chinese government emphasize the importance of the application of renewable energy like photovoltaic energy. Internationally, some countries and regions already have ability to replace fossil energy with renewable resources such as wind, solar, wind, and hydrogen energy. This thesis focuses on photovoltaic energy and its applications. Photovoltaic energy usually uses monocrystalline silicon and polysilicon as raw materials, and this paper compares the advantages and disadvantages of both raw materials. The technology of building PV integration, which combines PV cells with buildings, and the technology that increases the conversion efficiency of PV cells by passivating the back contact of the emitting area are described in detail. In addition, this study illustrates the reasons that limit the development of photovoltaic cells under the current technology in terms of both self-factors and environmental factors. The self-factors are mainly the conversion rate of its own materials and energy consumption of meta-components, and the environmental factors are mainly the geographical location leading to the solar altitude angle and the amount of solar radiation. In the future, the global PV market will continue to maintain a rapid growth trend, driven by favorable factors such as the continued decline in the cost of photovoltaic power generation and the positive market orientation


Introduction
With the concept of the Emission Peak and Carbon Neutrality proposing, Chinese government demonstrates that it is important for national energy to develop vigorously renewable energy such as photovoltaic power generation.In some certain spaces and countries, they have already able to compete with fossil fuels.Solar, wind, hydrogen and other new energy supply.In German, the government put forward 100,000 Roofs Program in 1998 and then put the plan into practice officially in 2000, which was a plan that encouraging residents to install solar photovoltaic systems on their roofs.In 2017, the Mexican Ministry of Energy clarified the goals and strategies for the development of clean energy production, proposing that the proportion of renewable energy in the total energy should reach 25% in 2018, 30% in 2021, 30% in 2024, 45% in 2036, and 60% in 2050.Like Italy, French, Netherlands and other countries, the governments have issued introduced grid pricing policies to accelerate investment in PV power generation [1].
By converting directly light energy into electricity, PV cells utilize the photovoltaic effect and photochemical effect.There is a mainstream which slight-film solar cells applying with the photovoltaic effect, although using photochemical effect of the principle of solar cells is still in its infancy.Sunlight irradiates on the semiconductor p-n junction, forming a new hole-electron pair.With the electric field of the p-n junction acting, the holes flow from the n-zone to the p-zone and the electrons flow from the p-zone to the nzone, and an electric current is formed when the circuit is lined [2][3].A single PV cell cannot be used directly as a power source so that an amount of individual cells must be connected in series and parallel and tightly packaged into modules for power supply.In detail, PV modules are composed of efficient monocrystalline or polycrystalline solar cells, low-iron ultra-white suede tempered glass, encapsulation materials, functional backsheets, interconnection strips, convergence strips, junction boxes and aluminum alloy frames.The using span of these modules can reach 15-25 years [4][5].
Herein, the aim of this article is to present in detail the photovoltaic energy sources that can replace traditional fossil energy sources in the context of energy scarcity.There are three major modules in this essay.First, different photovoltaic materials and applications from different technologies in photovoltaic cells are briefly described, such like Building Integrated PV (BIPV), passivation emitter and rear contact (PERC).Finally, its limitations are introduced from itself and the environment.
Monocrystalline silicon is a single silicon crystal that has a nearly flawless dot pattern.It is a decent semiconducting material since different directions have varied characteristics.The crystals of single crystal silicon have a diamond lattice, are tough and brittle, and have a metallic sheen that allows them to conduct electricity.However, although having semiconductor qualities, the conductivity is not as good as that of metal and improves with temperature.An essential semiconductor component is monocrystalline silicon.By adding trace elements to monocrystalline silicon, P-type N-type semiconductors are formed, one solar cell can be made, when they are combined.which convert radiation energy into electricity.Monocrystalline silicon solar cells are the highest developing type of solar cells, with the advantages of long service life, perfect preparation process and high conversion efficiency, and are the leading products in the photovoltaic market.At present, the share of monocrystalline solar cells in the PV market reaches more than 95% [6].

Polycrystalline silicon
Although the production process of both is similar, the photoelectric conversion efficiency and the energy consumption of polycrystalline silicon is much lower.Comparing with monocrystalline silicon solar cells, polycrystalline silicon solar cells have many benefits, such like the production process is pollution-free, it can save more electricity consumption and the production cost is cheap so that it has been developed in large numbers.

Monocrystalline silicon and polycrystalline silicon comparison
Using the material of crystalline silicon, solar cells have two types, monocrystalline silicon and polycrystalline silicon respectively.During the high-temperature refining process, polysilicon is internally contaminated due to contact with impurity materials, so it leads to high crystal defects.The conversion efficiency of polycrystalline silicon solar cells is often lower than that of monocrystalline silicon solar cells due to the role that crystal imperfections play as compound sites for photogenerated carriers and holes.However, polycrystalline silicon solar cell manufacturing is relatively simple and can achieve low-cost solar cell manufacturing, so it still holds a certain market share.Monocrystalline silicon is usually produced by the polycrystalline silicon drawing method.

Other materials
PPV-type photovoltaic materials, i.e., poly (p-phenylene vinylene) derivatives, are a widely used class of organic photovoltaic cell materials, which have better luminescence and photovoltaic properties [7].In the application of photovoltaic cells, mainly alkyl sidechain-substituted PPV-like materials are used, among which poly-2-methoxy-5-(2-ethyl-hexyloxy)-p-styrene (MEH -PPV) and poly [2-methoxy-5-(3′,7′ dimethyloctyloxy)]-p-phenylene propylene glycol (MDMO-PPV) are the most representative materials.Both of them are solar feeder materials.The combination of MEH-PPV and MD-MO-PPV feeders with different crystalline acceptor materials has become the focus of research to explore the preparation of new organic photovoltaic cell materials.
DPP-like materials are one of the more mature materials used to prepare photovoltaic cells with high hole mobility and charge carrier mobility, which exhibit better cell performance [8].It has been reported in the literature that the electrical conversion rate of DPP-like polymer photovoltaic cells can reach up to 8.08% [9].In the last two years, most of the studies have focused on how to change the molecular structure of DPP-like materials or to blend DPP with acceptors in different ratios to obtain the optimal combination, so as to explore the preparation of high-performance DPP photovoltaic cells.
PT materials are one of the most widely used materials in organic photovoltaic cells, which can be used in various fields such as electrochromic, photoelectric sensors and light-emitting diodes.The preferred material with good performance and promising application is 3 hexyl-substituted polythiophene (PH3T).
The BDT derivatives have good planarity, high mobility and high photovoltaic properties, with a maximum energy conversion rate of 11.21% [10].By changing the alkyl thiophene-based chains in BDT and adding alkyl side chains, it can achieve the effect of improving the cell performance.

BIPV technology
In China, building carbon emissions account for more than 30% of the country's total carbon emissions, with urbanization in China's building area continues to expand at a scale of about 2 billion m 2 per year, control of building carbon emissions is a problem that needs attention.Using of photovoltaic power generation is a method for energy saving and carbon reduction in buildings, and BIPV, in which photovoltaic modules are used as part of the building design, is considered to be the mainstream of the future development of building energy systems [11].BIPV is a new concept and method of applying solar power generation, which is based on the geography of the construction site, climate conditions, building function, surrounding environment and other factors for planning and design, determining the building layout, orientation, spacing, group combination and spatial environment, and it is a technology of intalling solar photovoltaic arrays on the outer surface of the building envelope to provide electricity and integrate solar power generation (photovoltaic) products into the building.
While enjoying the benefits of photovoltaic power generation, it is also necessary to take into account the basic functional requirements of the building, not to , 03009 (2023) affect the architectural function of the PV module installation site, and to maintain a unified and harmonious appearance of the building.Therefore, it is necessary to achieve the key points of integrated PV building design from two aspects: PV module form and wiring form.When carrying out the architectural design, the PV curtain wall BIPV components and the overall appearance of the building should be considered at the same time, so that the overall beauty and harmony.But it will make the power generation inevitably have a certain loss.Therefore, according to the needs of the architectural profession, additional color front panels can be installed.When applied to the light roof, colored PVB film BIPV solution can be used, which not only can reduce the product cost, but also will not reduce the photoelectric conversion efficiency of BIPV.
Secondly, when designing the integration of photovoltaic building, consider the light transmission rate of curtain wall and photoelectric conversion efficiency at the same time, generally the light roof can meet the demand by choosing 10% to 20% light transmission, and the area with higher light transmission of façade curtain wall can choose 40% or 50% light transmission.Finally, in the PV building integration design, should pay attention to the wiring form.There are many forms of curtain walls, different forms of PV curtain walls in the wiring, the location of the junction box, wiring parts, wiring form will not be consistent, in order to avoid arbitrariness, wiring adaptability can be selected [12].

PERC passivated emitter rear contact and "PERC+SE" technology
PERC (Passivated emitter rear contact) is a new type of high-efficiency solar cell technology that has been massproduced so far.By adding passivated Al2O3 and SiNx layers on the back side of the cell, and using a passivated partial contact structure, PERC technology improves the conversion efficiency of the cell.In details, Conventional aluminum back surface (BSF) cell structures are the natural source of PERC cells.Conventional BSF cells have an inherent limitation in the photovoltaic conversion efficiency because the back surface of the metal aluminum film layer in the composite speed cannot be reduced to below 200cm/s, resulting in the arrival of infrared radiation in the aluminum back layer of only 60-70% of the light can be reflected, increasing photoelectric losses; PERC technology by attaching a dielectric passivation layer in the back of the cell can overcome this limitation.Increasing the solar cell's 1% photoelectric conversion efficiency in the process.A cell and module invention is PERC.
Currently, PERC technology has been upgraded to "PERC+" technology, i.e. "PERC+ Selective Emitter (SE)" technology, and the "PERC+SE" monocrystalline solar cell with this technology has a higher conversion efficiency.The preparation process of "PERC+SE" monocrystalline solar cells using this technology is shown in Fig. 1.The application of selective emitter (SE) technology combined with passivated emitter back contact (PERC) technology (i.e., "SE+PERC") in monocrystalline silicon solar cells has further improved the photovoltaic conversion efficiency of monocrystalline silicon solar cells.The "SE+PERC" monocrystalline solar cell uses a laser doping process to selectively redope the emitter while reducing the contact resistance of the solar cell and altering the fill factor.In the non-laser doped area, high square resistance helps to increase the open circuit voltage and reduce circuit current, which boosts the efficiency of turning light into electricity [13].

Defects of photovoltaic cells 4.1 System loss
On the one hand, owing to silicon is important material of solar photovoltaic cells, the task is to boost the conversion rate of silicon material, which limits the further development of the entire industry.On the other hand, the energy generated by the PV modules goes through each component and produces the loss of energy.For example, through connectors, DC cables, sink boxes and other components, which consume electrical energy and generate electrical energy loss.Besides these natural aging factors, there are also other factors, such like the quality of every modules, line layout, dust, and so on.Generally, the power generation capacity decreases by 5% in three years, and decreases to 80% in 20 years.

Environmental factors
Affected by natural conditions can be divided into solar altitude angle and geographical latitude, atmospheric transparency and altitude, and sunshine hours.First, The sun's radiation strength has an impact on the sun's altitude angle.For instance, the sun's altitude angle will be smaller in high latitude regions, resulting in a weaker sun's radiation intensity, while the sun's altitude angle will be larger in low latitude regions, resulting in a stronger sun's radiation intensity.In conclusion, it is more practical to develop solar photovoltaic power generating in low latitude places.Second, influencing by geographic altitude, the transparency of air is a non-ignorant element, which has straight influence with the radiation of sunlight.Therefore, a suitable place depends on a high altitude and the great solar radiation energy.What's more, another essential factor influencing ground-based solar energy is the duration of illumination.

Conclusion
The application of photovoltaic cells is closely related to all aspects of human society, including environmental protection, energy utilization and industrial production.This paper introduces the basic components of photovoltaic cells, the principle of power generation.At present, most of the PV cells in the domestic market are made of monocrystalline silicon, which has the characteristics of long life, perfect preparation process and high conversion efficiency, but the production cost of polycrystalline silicon PV materials is lower.ppv PV materials, DPP materials, PT materials, BDT derivatives of these four types of PV materials are also widely used in PV cells.Building photovoltaic integration technology is in the application of photovoltaic cells to increase its practicality, and passivation emitting area back contact technology is from the root to increase its power generation efficiency, both are the mainstream of the current development of photovoltaic cell applications.Its own conversion efficiency, meta-component power consumption and other system factors, due to geographical changes in the amount of solar radiation due to the natural factors of the two factors resulting in power generation efficiency has been an important issue that restricts the photovoltaic cells.At present, China has realized the centralized and distributed type and at the same time innovated to create a variety of models such as water-light complementary, fishery-light complementary, agricultural-light complementary, etc., to achieve a steady increase in efficiency.In the future, with the continuous development of PERC and N-type bifacial module technology, the large-scale application of high-efficiency modules, the technological progress of energy storage system and the decrease of battery cost, PV + energy storage system will become a new development mode, and the coordinated power generation of water, light, wind and storage will become the future direction of clean energy development.