External quantum efficiency

Definition

External quantum efficiency (EQE) is a measure of how effectively a device, like an organic light-emitting diode (OLED) or a photovoltaic cell, converts injected charge carriers into emitted photons or electrical energy. EQE reflects the percentage of charge carriers that successfully contribute to light emission or electricity generation, making it a crucial parameter for evaluating the performance of these devices.

5 Must Know Facts For Your Next Test

1. EQE is expressed as a percentage, indicating the fraction of injected charge carriers that result in emitted photons in OLEDs or generated electricity in photovoltaics.
2. In OLEDs, high EQE is essential for creating bright displays with minimal energy consumption, while in photovoltaics, high EQE maximizes energy harvesting from sunlight.
3. Factors affecting EQE include material properties, device architecture, and the presence of non-radiative recombination processes that can reduce efficiency.
4. For OLEDs, achieving both high internal quantum efficiency (IQE) and high EQE is necessary for optimal performance, since IQE measures the number of excitons converted to photons within the device.
5. Improving EQE in both OLEDs and photovoltaics often involves optimizing layer thickness, materials selection, and device structures to minimize losses.

Review Questions

• How does external quantum efficiency influence the performance of organic light-emitting diodes?
  • External quantum efficiency significantly impacts the performance of organic light-emitting diodes by determining how many charge carriers contribute to light emission. A higher EQE means that more electrons and holes are effectively recombining to produce photons, leading to brighter displays and lower power consumption. In designing OLEDs, engineers aim to maximize EQE by using materials that enhance radiative recombination and reduce non-radiative losses.
• What are some key factors that affect the external quantum efficiency of photovoltaic cells?
  • Several factors influence the external quantum efficiency of photovoltaic cells, including the quality of the semiconductor materials used, the design of the cell structure, and how effectively it captures and utilizes sunlight. Additionally, minimizing recombination losses—both radiative and non-radiative—through careful engineering can significantly enhance EQE. The presence of anti-reflective coatings and light-trapping structures can also improve EQE by increasing the amount of light absorbed by the cell.
• Evaluate the relationship between external quantum efficiency and overall device performance in OLEDs and photovoltaics.
  • The relationship between external quantum efficiency and overall device performance in both OLEDs and photovoltaics is crucial for achieving optimal functionality. High EQE correlates with better brightness in OLEDs and greater energy output in photovoltaics, which enhances user experience and energy yield. Evaluating this relationship involves understanding how various design choices—like material selection and layer structuring—impact not only EQE but also other metrics like lifetime and stability, ultimately driving advancements in these technologies.

Related terms

Photoluminescence: The process by which a material absorbs photons and re-emits them, which is critical in determining the efficiency of light emission in OLEDs.

Power conversion efficiency: A metric used to assess how well a photovoltaic device converts sunlight into electrical energy, directly related to the concept of external quantum efficiency.

Charge carrier: Particles such as electrons or holes that carry electric charge through a material, playing a key role in the function of OLEDs and photovoltaic cells.