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s the world shifts towards renewable energy, solar power is gaining traction as a sustainable, abundant, and cost-effective option. Yet, with the increasing demand for solar, there's a pressing need for more efficient and economical solar cells. This is where multi junction solar cells steal the spotlight as a game-changer in the solar industry. These cells hold immense potential to transform the way we generate and consume solar energy, and this article explores what makes them so exciting.

Solar basics: How PV panels work to convert sunlight into electricity

To get started, let's grasp the fundamentals of how solar power functions. The use of solar panels, also known as photovoltaic (PV) panels, has transformed how we collect energy from the sun. The technology that powers solar panels may appear complicated, but it's really quite straightforward. When sunlight hits the panel’s surface, it is soaked up by solar cells that are made of semiconductor materials like silicon. This absorption of light makes the electrons in the semiconductor material of the cell excited and prompts them to break free from their atoms, allowing them to move through the material. This movement of electrons within the cell creates an electrical current that is then captured by the wiring within the panel and directed to an inverter, which converts it into usable electricity.

The limitations of conventional single junction solar cells

Single junction solar cell technology, while instrumental in progressing solar energy production, has its drawbacks. A major limitation is its incapacity to capture a broad range of the solar spectrum. Consequently, a significant amount of sunlight hitting the cell is either reflected, converted to heat or absorbed but not converted into electricity, leading to a very limited efficiency ceiling. In fact, even the most ideal single junction solar cell with a band gap that is optimal for the solar spectrum can achieve only a theoretical maximum efficiency of 33.16%, according to the Shockley-Queisser limit.
Silicon solar panels are the most widely used photovoltaic technology, harnessing sunlight to generate electricity efficiently and sustainably.

Introduction to multi junction solar cells

In response to the challenge of inadequate solar spectrum absorption, scientists have engineered multi junction solar cells. Instead of the usual single junction solar cell that employs a single semiconductor layer to capture sunlight, a multi junction cell uses several layers of different materials stacked one upon the other, each tailored to absorb a specific part of the solar spectrum. This unique feature enables the cell to convert more of the incoming solar energy into electricity, thereby achieving superior conversion efficiency.

The science behind multi layered photovoltaics

The most commonly used material for solar cells is silicon, which is used in single junction crystalline solar cells that have an n-type layer from a p-type layer separated by a p-n junction. However, multi junction solar cells take this technology to the next level by incorporating multiple p-n junctions made of different semiconductor materials, such as gallium indium phosphide, indium gallium arsenide, and germanium. This means that multi junction cells can absorb a broader range of wavelengths of the solar spectrum and convert them into electricity, making them more efficient than single junction solar cells.

How multi junction solar cells work

Similar to traditional single junction silicon solar cells, multi junction solar cells also rely on the photovoltaic effect to produce electricity. The process entails the absorption of light, which knocks electrons loose in the semiconducting material. The electrons then traverse the p-n junction between the semiconductor layers of the cell, generating an electrical current that is captured and transferred to wires.

However, a multi junction cell has the advantage of possessing several p-n junctions, as opposed to a single junction solar cell. This design results in a more efficient conversion of sunlight into electrical energy, with each junction optimized to capture a particular light wavelength.

Efficiency gains of a multi junction solar cell over single junction solar cell

Solar efficiency refers to the amount of sunlight that can be converted into electricity. Efficiency-wise, a multi junction cell outshines a regular single junction solar cell. The Department of Energy reports that triple junction solar cells can achieve efficiencies of over 45%, whereas single junction cells max out at around 33.5%. With the addition of more junctions (up to five or six), efficiency could exceed 70%, making them a significant improvement over most efficient solar panels with single junction cells currently available, with efficiencies of around 22%.

Applications of multi junction solar cells

One of the main applications of multi junction solar cells is in space exploration, where the high efficiency and durability of these solar cells make them ideal for powering satellites and other spacecraft. Multi junction cells are also increasingly being used in terrestrial applications, particularly in concentrated photovoltaic (CPV) systems that focus sunlight onto small, high-efficiency solar cells. These systems are particularly useful in regions with high levels of direct solar irradiance, such as deserts, and can be used to generate electricity for both commercial and residential use.

Challenges and limitations of multi junction solar cell technology

Cost and scalability issues of multi junction solar cells

Multi junction cells come with a far more intricate design and involve the use of multiple semiconductor materials, which ultimately makes their production costs much higher than those of traditional single junction cells. This cost differential currently presents a hurdle for multi junction cells to break into the solar market and explains why they are not yet widely accessible.

Moreover, the scalability of these solar cells remains a challenge since they have been limited to space applications, requiring considerable investment in manufacturing infrastructure and research to extend their usage to terrestrial applications.

Technological and engineering challenges

In addition to cost and scalability concerns, these cells face major technological and engineering hurdles. The primary challenge is to create materials capable of withstanding harsh environmental conditions, including temperature fluctuations, humidity, and UV radiation, on our planet.

Furthermore, the manufacturing of multi junction solar cells necessitates precise control of the deposition of multiple semiconductor material layers, which can be a daunting task when scaled up. Moreover, factors such as shading, non-uniform illumination, and thermal gradients can affect the performance of the cells. To conquer these challenges, advanced tracking and cooling systems must be developed to optimize solar cell performance under real-world conditions.

The future of solar technology: The role of multi junction cells

To wrap it up, multi junction cells are a cutting-edge technology with enormous potential to revolutionize solar power in the coming years. By capturing a broader range of the sun's spectrum and converting it into energy more efficiently, these cells offer a clear path to cost-effective and sustainable solar energy. Experts predict that the multi junction solar cells market will reach a whopping $3.5 billion by 2025.

However, more research and development are necessary to make this multi junction solar cell technology more affordable and scalable for a broader audience. With continued investment and innovation, multi junction solar cells could transform the energy industry and create a more sustainable and resilient future.

Sources:

https://www.energy.gov/eere/solar/multijunction-iii-v-photovoltaics-research

https://www.industryarc.com/Report/19363/multi-junction-solar-cells-market.html

Posted 
May 9, 2023
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