What is the Difference Between Internal and External Quantum Efficiency?

The key difference between internal and external quantum efficiency lies in the way they are calculated and the factors they consider. Quantum efficiency (QE) is a measure of the ratio of charge carriers collected by a solar cell to the number of photons incident on the cell. It can be classified into two types:

1. Internal Quantum Efficiency (IQE): This is the ratio of the number of charge carriers collected by the solar cell to the number of photons of a given energy that penetrate the material and are not reflected or transmitted out of the cell. IQE is always calculated when the incident is on the inside of the material and considers the photons that actually enter the solar cell material. It accounts for the efficiency with which photons generate collectable charge carriers within the solar cell.
2. External Quantum Efficiency (EQE): This is the ratio of the number of charge carriers collected by the solar cell to the total number of incident photons, considering the photons shining from outside the material. EQE does not depend on the interface reflection or penetration and calculates the total number of incident photons. It includes the effect of optical losses such as reflection and transmission.

In summary, the main differences between internal and external quantum efficiency are:

• IQE is calculated using the photons that penetrate the material and are not reflected or transmitted out of the cell, while EQE is calculated using the total number of incident photons.
• IQE accounts for the efficiency with which photons generate collectable charge carriers within the solar cell, while EQE includes the effect of optical losses such as reflection and transmission.

Comparative Table: Internal vs External Quantum Efficiency

The key difference between internal and external quantum efficiency is that internal quantum efficiency is calculated using the photons that are not reflected or transmitted out of the cell, while external quantum efficiency is calculated using the total number of incident photons, including those that are reflected or transmitted. Here is a table summarizing the differences between internal and external quantum efficiency:

In summary, internal quantum efficiency focuses on the efficiency of photon conversion within the solar cell, while external quantum efficiency accounts for the total number of incident photons, including those that are not absorbed by the cell.