External quantum efficiency

Definition

External quantum efficiency (EQE) is a measure of how effectively a solar cell converts incident photons into usable electrical current. It is defined as the number of charge carriers collected by the device per incident photon, reflecting the effectiveness of light absorption, charge generation, and collection processes. A high EQE indicates that a device can utilize a larger fraction of the incoming light, which is critical for improving the performance of photovoltaic cells in various structures and configurations.

5 Must Know Facts For Your Next Test

1. EQE can vary with wavelength; solar cells may have higher efficiencies for certain wavelengths due to material properties and band gaps.
2. In tandem and inverted devices, optimizing EQE is essential as multiple layers can absorb different parts of the solar spectrum, enhancing overall performance.
3. Light management strategies, such as using anti-reflective coatings or texture on the surface, can significantly increase EQE by reducing reflection losses.
4. EQE is typically measured under specific conditions, such as monochromatic light sources, to obtain accurate data on how well a cell converts different wavelengths into electricity.
5. Improving EQE is a key goal in designing new materials and structures for organic photovoltaics to maximize energy conversion efficiency.

Review Questions

• How does external quantum efficiency influence the overall performance of inverted and tandem solar cell structures?
  • External quantum efficiency is crucial in inverted and tandem solar cell structures because it directly affects how much of the absorbed light is converted into electrical energy. In these designs, each layer can be optimized for specific parts of the light spectrum, leading to higher overall EQE. The ability to achieve high EQE across multiple layers ensures that more photons contribute to electricity generation, which is vital for maximizing power output.
• What role does light management play in enhancing the external quantum efficiency of organic photovoltaics?
  • Light management techniques are essential for enhancing external quantum efficiency because they help capture more incoming light and minimize losses due to reflection or suboptimal absorption. By incorporating features such as textured surfaces, anti-reflective coatings, and light-trapping structures, organic photovoltaic devices can increase the number of photons that enter the active layer. This improved light interaction directly translates into higher EQE, leading to better overall device performance.
• Evaluate how optimizing external quantum efficiency could impact future developments in tandem solar cell technology.
  • Optimizing external quantum efficiency could significantly impact future developments in tandem solar cell technology by enabling these devices to achieve higher power conversion efficiencies. By focusing on materials and architectures that enhance EQE across the spectrum, researchers can create tandem cells that outperform traditional single-junction cells. As new materials are developed and layered configurations are refined to maximize EQE, this advancement could lead to substantial reductions in cost per watt and increased adoption of solar technologies in various applications.

Related terms

Photovoltaic effect: The process by which a solar cell converts light energy into electrical energy through the generation of charge carriers.

Charge carrier: An electron or hole that carries electric charge within a material, playing a crucial role in the conduction process in solar cells.

Absorption spectrum: A spectrum that shows the range of wavelengths of light absorbed by a material, which is important for understanding how efficiently a solar cell can capture light.