## Quantum efficiency in photovoltaics

Quantum efficiency in photovoltaics is the ratio of electrons in a photocurrent to the number of photons that hit, for example, a solar cell. Since no one wants to count individual electrons or photons, it is common to compare the component that is to be tested with a calibrated element. The unknown quantum efficiency QE is results from the following:

$$QE = QE_{kal} * \frac{I_{mess}}{I_{kal}}$$

QEkal is the quantum efficiency of the calibrated component, and the quotient is the ratio of the two generated currents. This is subject to both cells being irradiated with the same luminous intensity. The image shows a typical QE measurement setup (here: on a photodiode). On the left side radiation of a specified wavelength (energy) is created. The chopper creates lighting packages of a determined frequency. On the right you can see an M81 with two current measurement pods. The main system M81-SSM entangles and measures the two currents (Imess and Ikal) which occur at the photodiodes, with reference to the chopper frequency and phase.

Compared to the classic measurement setup with two preamplifiers and two lock-in channels, this system not only saves hardware but also gains metrological flexibility. For example, the M81 allows DC measurements like current/voltage characteristic (IV) curves or creating a bias (by using additional pods, if necessary). In the table, you will find the specifications of the combination M81-SSM with the current measure module CM.
In principle, quantum efficiency can also be measured on other opto-electronic components, like phototransistors, photomultipliers, photocathodes, solar cells and image intensifiers.

#### M81 CM-10 Current measure module

• Frequency: DC to 100 kHz
• Best sensitivity: 10 fA
• Max. range: 100 mA
• Bias voltage: +/-10 V

Nicolas Tcherbak

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