SE1x_2022_Week_4_2_Solar_cell_losses_and_design_part_2-video

Summary

This video covers the fundamentals of crystalline silicon solar cells, detailing the various losses that affect their performance. It explores optical losses like spectral mismatch, reflection, and transmission, as well as electrical losses such as recombination and resistive losses. The video introduces the basic design of solar cells, highlighting key mechanisms like parasitic absorption and shading losses. It also discusses how the series and shunt resistances influence energy efficiency. Finally, the video ties these concepts to solar cell design rules and prepares viewers for the next course on photovoltaic materials and technologies, offering insights into industry practices and challenges.

Takeaways

• 😀 Spectral mismatch losses occur in solar cells, affecting energy conversion efficiency.
• 😀 Additional optical losses include reflection and transmission losses, shading, and parasitic absorption.
• 😀 The metal grid on solar cells causes shading, decreasing the amount of sunlight reaching the absorber layer.
• 😀 The glass encapsulating the solar modules reflects a portion of incident light, reducing the amount of light entering the solar cell.
• 😀 Parasitic absorption occurs when light is absorbed in layers that do not contribute to charge carrier generation, particularly in p-i-n junction solar cells.
• 😀 Transmission losses happen when photons pass through the solar cell without being absorbed, especially those with energy close to the bandgap.
• 😀 Recombination losses occur when an excited electron returns to its initial energy state, preventing energy conversion.
• 😀 There are three main types of recombination: radiative, Auger, and Shockley-Read-Hall (SRH).
• 😀 Auger recombination involves a three-particle process where energy is transferred to another particle, which then relaxes thermally.
• 😀 Electrical losses in solar cells also include resistive series losses and shunt losses, which impact the overall efficiency.

Q & A

What are some of the additional losses that occur in crystalline silicon (c-Si) solar cells?

The additional losses in c-Si solar cells include reflection and transmission losses, parasitic absorption, and shading losses caused by the metal grid and glass encapsulation.

How does the metal grid impact solar cell efficiency?

The metal grid causes shading, blocking sunlight from reaching the absorber layer, thereby decreasing the amount of sunlight that can be converted into electrical energy.

Why does the glass plate used in solar modules cause reflection losses?

The glass plate reflects a fraction of the incoming light, reducing the amount of light absorbed by the solar cell despite the high transparency of silicon dioxide to visible light.

What is parasitic absorption in the context of solar cells?

Parasitic absorption occurs when light is absorbed in non-photovoltaic layers of the solar cell, which does not contribute to charge carrier generation and represents a loss in energy conversion.

What are transmission losses in solar cells?

Transmission losses happen when photons pass through the solar cell without being absorbed, typically occurring with photons that have energy equal to or slightly above the bandgap energy, which are less likely to be absorbed.

What are recombination losses in solar cells?

Recombination losses occur when an electron, after excitation, falls back to its initial energy state, causing the absorbed energy to be lost and not converted into electrical energy.

What are the three types of recombination mentioned in the video?

The three types of recombination are radiative recombination, Auger recombination, and Shockley-Read-Hall (SRH) recombination.

How does radiative recombination differ in direct and indirect bandgap semiconductors?

In direct bandgap semiconductors, radiative recombination is significant, where energy is emitted as a photon. In indirect bandgap semiconductors like crystalline silicon, radiative recombination is relatively rare.

What is Auger recombination?

Auger recombination is a three-particle process where the energy and momentum of recombining carriers are transferred to a third electron or hole, which is excited into a deeper band and then relaxes through thermalization.

What causes resistive losses in solar cells, and how do they affect efficiency?

Resistive losses are caused by series resistance from bulk semiconductor material and metal contacts, as well as shunt resistance from current leakage. These losses reduce the solar cell's output power and efficiency.

How do the resistive and shunt resistances affect the current in a solar cell?

The series resistance reduces the maximum output power, so it should be kept low. Shunt resistance, when low, acts as a current sink and decreases the power delivered to the load, so it should be kept high.

What are the three major solar cell design rules derived from the discussed loss mechanisms?

The three major design rules are spectral utilization (to address spectral mismatch losses), light management (to minimize optical losses), and bandgap utilization (to reduce electrical losses like recombination and resistive losses).

What is the significance of understanding these loss mechanisms in solar cell design?

Understanding these loss mechanisms helps in designing more efficient solar cells by targeting specific losses in optical and electrical processes, leading to improved energy conversion and performance.