4.4 High-Efficiency Concepts of c-Si Wafer Based Solar Cells

Summary

This video script delves into high-efficiency crystalline silicon solar cells, exploring three advanced technologies: the PERL solar cell, the Interdigitated Back Contact (IBC) solar cell, and the Crystalline Wafer-based Heterojunction (HIT) solar cell. It covers their design concepts, materials, and innovations aimed at minimizing losses and enhancing efficiency, including surface passivation, anti-reflection coatings, and rear surface fields. The script highlights the advantages of monocrystalline wafers, n-type silicon, and heterojunctions for achieving high efficiency, with record solar cell performances like 25% for PERL, 24.2% for IBC, and 24.7% for HIT. The video concludes with insights into solar cell production and module creation.

Takeaways

• 😀 The PERL solar cell, developed by Martin Green’s group, achieved efficiencies near 25% by minimizing optical losses with textured surfaces, anti-reflection coatings, and thin metal contacts.
• 😀 The Interdigitated Back Contact (IBC) solar cell, created by SunPower, eliminates front-side shading losses by placing contacts on the rear, utilizing n-type wafers for reduced degradation.
• 😀 N-type wafers used in the IBC solar cells are more resistant to light-induced degradation and impurities compared to p-type wafers, making them more cost-effective and durable.
• 😀 The IBC solar cell’s interdigitated design separates p- and n-type contacts at the back, reducing recombination and resistive losses for improved efficiency.
• 😀 The Heterojunction (HIT) solar cell by Panasonic uses a combination of monocrystalline silicon and amorphous silicon, achieving high open-circuit voltages (750 mV), the highest for crystalline silicon technologies.
• 😀 HIT cells passivate charge carrier surfaces with thin layers of amorphous silicon, which results in improved carrier lifetimes and bifacial light collection (from both front and rear).
• 😀 HIT solar cells utilize transparent conductive oxide (ITO) layers for current collection, addressing the poor conductivity of p-type amorphous silicon.
• 😀 Panasonic's HIT solar cell efficiency reached 24.7%, demonstrating the effectiveness of its bifacial configuration and surface passivation techniques.
• 😀 Record efficiencies for crystalline silicon-based cells include: 25% for PERL (lab-scale), 24.2% for IBC (SunPower), and 24.7% for HIT (Panasonic).
• 😀 Multicrystalline silicon cells typically have lower efficiencies, with Q-cells achieving a best efficiency of 19.5%, about 5% less than monocrystalline-based technologies.

Q & A

What is the PERL concept in crystalline silicon solar cells?

The PERL concept, developed by Martin Green's group at the University of New South Wales, stands for Passivated Emitter Rear Locally Diffused. It minimizes optical losses at the front side of the solar cell using textured surfaces, a double-layer anti-reflection coating, and thin metal fingers. It also focuses on reducing surface recombination with a passivated emitter and rear surface field.

How does the PERL concept improve efficiency in solar cells?

The PERL concept improves efficiency by reducing optical losses with textured surfaces and a double-layer anti-reflection coating. It also suppresses surface recombination with a passivated emitter and rear surface field, leading to an open-circuit voltage above 700 mV.

What are the advantages of using n-type wafers in solar cells, particularly in interdigitated back contact (IBC) cells?

N-type wafers offer advantages over p-type wafers, such as resistance to light-induced degradation and lower sensitivity to impurities like iron. This results in better stability and potentially lower costs due to easier processing of high-quality n-type silicon.

What is the role of back contact technology in solar cells?

Back contact technology, as used in interdigitated back contact (IBC) solar cells, eliminates shading losses by positioning all the metal contacts at the rear of the solar cell. This allows for larger contact areas, reducing resistive losses, and the use of passivation layers that act as backside mirrors to improve light absorption.

What is the difference between homojunction and heterojunction solar cells?

A homojunction solar cell is made from a single semiconductor material with p-type and n-type regions. In contrast, a heterojunction uses two different semiconductor materials, such as n-type crystalline silicon and p-type amorphous silicon, resulting in different band gaps and creating an energy barrier for charge carrier separation.

What are the key benefits of the HIT (Heterostructure with Intrinsic Thin Film) solar cell?

The HIT solar cell, developed by Panasonic, combines a thin layer of amorphous silicon with n-type crystalline silicon, offering high open-circuit voltages and excellent passivation of charge carrier recombination. The amorphous silicon layers are deposited at low temperatures using inexpensive techniques, making it a cost-effective solution for high-efficiency cells.

Why is amorphous silicon used in heterojunction solar cells?

Amorphous silicon is used in heterojunction solar cells because it provides excellent passivation, reducing charge carrier recombination at the surface. Its ability to be doped with both p-type and n-type properties also helps in forming efficient junctions with crystalline silicon.

How does the HIT solar cell achieve its high open-circuit voltage?

The HIT solar cell achieves high open-circuit voltage by using thin layers of intrinsic and doped amorphous silicon on both the front and rear surfaces of the n-type crystalline silicon wafer. This design minimizes surface recombination and maximizes charge carrier lifetimes.

What is the importance of using double-layer anti-reflection coatings in high-efficiency solar cells?

Double-layer anti-reflection coatings are crucial in high-efficiency solar cells, as they significantly reduce surface reflection, allowing more light to enter the cell and be absorbed. This enhances the overall efficiency by improving the amount of light that is coupled into the solar cell.

How does the interdigitated back contact (IBC) solar cell minimize shading losses?

The interdigitated back contact (IBC) solar cell minimizes shading losses by placing all the metal contacts on the back of the solar cell. This arrangement eliminates the need for a front metal contact grid, which would otherwise block incoming sunlight and reduce efficiency.