CURRENT STATE AND FUTURE TRENDS IN SOLAR PHOTOVOLTAIC TECHNOLOGIES

Date: 30-Aug-2024, Author: KK Yadhunath, Senior Vice President - Manufacturing

Solar photovoltaic (PV) technology has come a long way, and now offers a wide range of options based on different silicon doping methods, wafer technologies, and more advanced cell-making techniques. The goal of this blog is to help you understand the different types of solar photovoltaic technologies that are available today by breaking down the main differences between them and updating on new developments.

SOLAR PV TECHNOLOGIES BASED ON SILICON DOPING

The performance of solar cells depends on the type of doping used in the silicon wafer. Doping is the process of introducing impurities into the silicon to modify its electrical properties, resulting in two primary types of solar cells: P-type and N-type.

P-Type Solar Cells

P-type solar cells are a common type of silicon-based photovoltaic cell. They are distinguished by the type of doping used in the silicon wafer, which affects their electrical properties. In P-type solar cells, the silicon wafer is doped with a material that creates a “positive” type of semiconductor.

In P-type silicon, the base material (usually silicon) is doped with an element from Group III of the periodic table, such as Boron. This doping introduces “holes” (positive charge carriers) into the silicon crystal structure. These holes are places where an electron is missing, allowing other electrons to move and conduct electricity. A P-type solar cell is typically paired with an N-type layer (doped with an element from Group V, such as Phosphorus) to form a P-N junction. The P-N junction is crucial for the photovoltaic effect, where light is converted into electricity. When sunlight hits the P-N junction, it generates electron-hole pairs. The electric field at the junction separates these charge carriers, with electrons moving toward the N-type side and holes moving toward the P-type side, creating an electric current that can be harnessed.

Examples of P-Type Solar Cells:

  • Standard Mono Crystalline Silicon Solar Cells: Most conventional silicon solar cells are P-type. These cells are made from a single silicon crystal, and have been widely used in residential and commercial solar installations before the advent of higher efficient ones.
  • Polycrystalline (or Multi Crystalline) Silicon Solar Cells: These are another common type of P-type cell, made from silicon crystals that are melted together. They are generally less efficient than monocrystalline cells, but still used to be widely used.
  • PERC (Passivated Emitter and Rear Cell) Solar Cells: While PERC technology can be used with both P-type and N-type silicon, many PERC cells use a P-type base. PERC cells have a passivated rear surface that improves efficiency by reducing recombination losses.

P-type solar cells have been the most popular technology in the photovoltaic industry because they were cheap and easy to make. However, these cells break down easily when exposed to light, and aren’t as efficient as some more advanced cell technologies.

image

N-Type Solar Cells

N-type solar cells are a type of silicon-based photovoltaic cell that utilizes a different doping process compared to P-type cells. In N-type solar cells, the silicon wafer is doped with an element from Group V of the periodic table, such as Phosphorus. This doping introduces an excess of electrons (negative charge carriers) into the silicon crystal structure. N-type cells are paired with a P-type layer to form a P-N junction. The P-N junction is essential for creating an electric field that separates and directs the electron-hole pairs generated by sunlight. When sunlight hits the P-N junction of an N-type solar cell, it generates electron-hole pairs. The electric field at the junction causes electrons to move toward the N-type side and holes toward the P-type side, creating an electric current that can be harnessed.

Examples of N-Type Solar Cells:

  • HJT (Heterojunction) Solar Cells: HJT cells use an N-type silicon wafer with thin layers of amorphous silicon on both sides. This technology combines the benefits of both silicon types and improves efficiency.
  • TOPCon (Tunnel Oxide Passivated Contact) Solar Cells: These cells use an N-type silicon wafer with a thin tunnel oxide layer and a passivated contact. This structure enhances cell efficiency and performance.
  • IBC (Interdigitated Back Contact) Solar Cells: IBC cells use an N-type silicon wafer with all electrical contacts located on the rear of the cell. This design minimizes shading and improves efficiency.

N-type solar cells offer significant advantages in terms of efficiency, performance, and durability, especially in terms of reduced light-induced degradation and better high-temperature performance. However, these benefits come with higher production costs and manufacturing complexity. As the technology advances and becomes more widely adopted, it is expected that the costs will decrease, making N-type solar cells a more attractive option for high-performance photovoltaic systems.

SOLAR PV TECHNOLOGIES BASED ON WAFER TYPES

The type of silicon wafer used in a solar cell also affects its performance and cost. Two dominant wafer technologies are monocrystalline and multi crystalline (polycrystalline).

Monocrystalline Technology

Monocrystalline solar technology utilizes silicon wafers cut from a single, continuous crystal structure. This uniform crystal lattice provides high purity and efficiency, allowing these panels to convert more sunlight into electricity compared to other types. The manufacturing process involves pulling a single crystal from molten silicon, resulting in cells with a characteristic dark black appearance. Monocrystalline panels typically offer better performance in terms of space efficiency and lower temperature coefficients than multi crystalline. The typical module efficiency with latest cell making technologies has crossed 22% and moving up.

Multi crystalline Technology

Multi Crystalline solar technology, also known as polycrystalline, involves the use of silicon wafers made from multiple silicon crystals melted together. This method is less expensive and simpler than producing monocrystalline cells, making multi crystalline panels a lower cost choice. But, multi crystalline panels typically have slightly lower efficiency compared to monocrystalline panels due to the boundaries between silicon crystals causing energy loss. Their production process results in a characteristic speckled blue appearance. The typical efficiency range for multi crystalline solar modules is 15 to 17%.

Thin Film Technology

Thin film solar technology involves depositing photovoltaic materials in extremely thin layers onto substrates like glass, plastic, or metal. Unlike traditional silicon-based panels, thin film cells use materials such as cadmium telluride (CdTe), amorphous silicon (a-Si), or copper indium gallium selenide (CIGS). These panels are lightweight, flexible, and can be manufactured at lower costs, making them suitable for a variety of applications, including building-integrated photovoltaics and portable devices. However, they generally have lower efficiency compared to crystalline silicon panels and require more space to generate equivalent power. Despite this, their versatility and cost-effectiveness make thin film technology a valuable option in solar energy. Typical module efficiency if 12 to 14%

Perovskite Technology

Perovskite solar technology is an emerging and promising innovation in photovoltaics, utilizing materials with a perovskite crystal structure, often a hybrid of organic and inorganic compounds. This technology offers several advantages, including high power conversion efficiency and lower production costs. Perovskite solar cells are known for their excellent light absorption and charge transport properties, which contribute to their high efficiency. They can be manufactured using simpler and less expensive methods compared to traditional silicon cells. However, challenges such as long-term stability and environmental impact still need to be addressed. Despite these hurdles, perovskite technology holds significant potential for the future of solar energy. Typical module efficiency has crossed 26% and moving up.

Tandem Technology

Tandem solar technology enhances photovoltaic efficiency by stacking multiple layers of solar cells, each designed to capture different segments of the solar spectrum. Typically, a tandem cell combines a high-efficiency perovskite layer with a traditional silicon layer. This configuration allows the perovskite layer to absorb high-energy blue and ultraviolet light, while the silicon layer captures lower-energy red and infrared light. By utilizing both layers, tandem solar cells can achieve higher overall efficiency than single-junction cells. Although more complex and expensive to manufacture, tandem technology holds significant promise for increasing energy output and advancing solar power’s role in meeting global energy needs. Typical module efficiency has crossed 34% and moving up.

SOLAR PV TECHNOLOGIES BASED ON CELL MAKING PROCESSES

Several advanced manufacturing processes have emerged to enhance the efficiency and versatility of solar cells. These include:

Mono PERC Module Technology

Mono PERC (Monocrystalline Passivated Emitter Rear Cell) technology represents a significant advancement in solar photovoltaic systems, enhancing both efficiency and performance. This technology builds upon traditional monocrystalline solar cells by introducing a passivation layer on the rear side of the cell. This layer, typically made of silicon dioxide or silicon nitride, reduces the electron-hole recombination that occurs when electrons and holes meet, which otherwise would lead to energy losses. By minimizing these recombination losses, Mono PERC cells can capture and convert more sunlight into electrical energy. Additionally, Mono PERC panels are designed to perform better in low-light conditions and have a lower temperature coefficient, meaning they maintain higher efficiency in high-temperature environments compared to standard panels.

This makes Mono PERC technology particularly valuable for installations in areas with high ambient temperatures or limited space. The improved efficiency translates to more power output per square meter, optimizing the use of available space. As a result, Mono PERC solar panels are increasingly favored for both residential and commercial solar energy systems. Their higher performance, combined with advances in manufacturing, has made them a cost-effective and reliable choice for today’s solar energy applications.

Bifacial Module Technology

Bifacial solar technology represents a significant advancement in photovoltaic systems by allowing solar panels to capture sunlight from both the front and rear sides, thereby increasing energy production. Unlike traditional monofacial panels, which only utilize the sunlight striking the front surface, bifacial panels are designed with a transparent back sheet or glass that enables light to penetrate and be absorbed from both directions. This design takes advantage of reflected light from the ground, buildings, or other surfaces, boosting the overall energy yield.

One of the primary benefits of bifacial technology is its ability to generate more electricity per square meter compared to conventional panels, especially in environments with high albedo surfaces such as snow-covered or reflective surfaces. Additionally, bifacial panels typically have a lower temperature coefficient, which means they perform more efficiently in higher temperatures. The increased power output and improved efficiency make bifacial panels particularly advantageous for large-scale commercial and utility-scale solar installations. As solar technology continues to evolve, bifacial panels are becoming an increasingly popular choice for maximizing the performance of solar energy systems.

Topcon Module Technology

TOPCon (Tunnel Oxide Passivated Contact) technology is a cutting-edge advancement in solar cell design that enhances the efficiency and performance of photovoltaic systems. This technology introduces a thin tunnel oxide layer between the silicon wafer and a passivated contact layer, typically composed of silicon. The tunnel oxide layer, only a few nanometers thick, acts as a barrier that reduces electron recombination and improves the cell’s overall energy conversion efficiency. By minimizing these recombination losses and enhancing the electrical contact, TOPCon cells can achieve higher power output compared to traditional solar cells.

TOPCon technology offers several advantages over other high-efficiency solar cell designs, such as PERC (Passivated Emitter Rear Cell). It provides improved temperature coefficient performance, which means the cells maintain higher efficiency in hot conditions, making them suitable for a wide range of climates. Additionally, TOPCon cells generally have lower manufacturing costs compared to some other high-efficiency technologies, making them a cost-effective solution for both residential and commercial solar applications. As the solar industry continues to seek ways to increase efficiency and reduce costs, TOPCon technology stands out as a promising advancement that could play a significant role in the future of solar energy.

HJT Module Technology

HJT (Heterojunction Technology) represents a revolutionary leap in solar cell technology, combining the advantages of both crystalline silicon and thin-film technologies to deliver superior performance and efficiency. HJT cells are constructed with a monocrystalline silicon wafer sandwiched between layers of amorphous silicon. This unique structure creates a heterojunction, which optimizes the cell’s ability to convert sunlight into electricity. The amorphous silicon layers act as passivation layers that reduce electron recombination losses, leading to higher efficiency than conventional silicon solar cells.

One of the key benefits of HJT technology is its exceptional performance in high-temperature conditions and low-light environments, making it highly versatile for various geographical locations. HJT cells also exhibit a lower temperature coefficient, meaning their efficiency is less affected by heat compared to traditional cells. This results in better energy output in warmer climates. Additionally, HJT technology allows for thinner and more flexible panels, which can be advantageous in applications requiring lightweight or curved solar modules. Despite the higher initial cost of manufacturing, the superior efficiency and performance of HJT cells make them a promising option for both residential and commercial solar installations.

IBC Module Technology

IBC (Interdigitated Back Contact) technology is an advanced design in solar cell technology that significantly enhances efficiency and performance by optimizing the way electrical contacts are integrated into the cell. Unlike traditional solar cells where contacts are placed on the front surface, IBC cells position all electrical contacts on the rear side of the cell. This design eliminates the need for metal grid lines on the front, which reduces shading and allows more sunlight to reach the silicon wafer, leading to increased energy conversion efficiency.

The IBC technology utilizes a grid of interdigitated fingers and contact pads on the back side of the cell, which improves the cell’s overall performance by minimizing resistive losses and maximizing light absorption. This innovative design results in higher efficiency compared to conventional solar cells, making IBC technology particularly suitable for high-performance applications. Additionally, IBC cells often have a lower temperature coefficient, meaning they perform better in hot conditions, and they offer improved aesthetic appeal due to the absence of visible metal lines on the front.

Flexible Solar Panels

Flexible solar panels represent an innovative leap in photovoltaic technology, offering versatility and adaptability that traditional rigid panels cannot match. Unlike conventional panels made from crystalline silicon, flexible solar panels typically use thin-film technologies such as amorphous silicon, cadmium telluride (CdTe), or copper indium gallium selenide (CIGS). These materials are deposited on flexible substrates like plastic or thin metal foils, allowing the panels to bend and conform to various surfaces.

One of the key advantages of flexible solar panels is their lightweight and adaptable nature, making them ideal for applications where traditional panels might be impractical. They can be integrated into a wide range of surfaces, including curved or irregular shapes, and are well-suited for use on vehicles, portable electronics, and building-integrated photovoltaics (BIPV). Additionally, flexible panels can be more resistant to breakage and impact compared to rigid panels, enhancing their durability in certain conditions.

However, flexible solar panels generally have lower efficiency compared to their rigid counterparts and may be less durable over time. Despite these trade-offs, their unique attributes open up new possibilities for solar energy integration in diverse and unconventional applications, pushing the boundaries of where and how solar power can be harnessed.

CONCLUSION

The world of solar PV technology is constantly evolving, with innovations in doping processes, wafer types, and cell-making methods driving higher efficiencies and better performance. Whether you’re choosing cost-effective polycrystalline panels or cutting-edge technologies like TOPCon or IBC, understanding the strengths of each option can help you make an informed decision for your solar energy needs.

As the industry progresses, technologies like perovskite and tandem solar cells may revolutionize the market, offering unprecedented efficiency in future solar panels.

Are you considering solar panels for your business? Orb Energy is here to help. Fill in the form for a free consultation.