Solar Cell Measurement

Core to any analysis of a solar cell or photovoltaic module is the assessment of its energy conversion efficiency. In a laboratory, this is typically done by using a solar simulator in combination with high-precision electronics. The solar simulator should be as close to the standardised solar spectrum as possible. This solar cell spectrum is defined in standards such as the IEC AM1.5G [1]. Also, the solar simulator should also have a sufficiently short and long-term stability and uniformity. The requirements are summarised in Table I and II. Solar simulators are quantified in Classes A to C, where A is the best and C the worst in terms of the spectral match, uniformity, and temporal stability.

The solar cell is placed on a temperature-controlled chuck, typically maintaining the temperature at 25 oC. The front of the solar cell is contacted using bars with various current-voltage pins, while a full area copper chuck typically contacts the rear of the solar cell with one voltage probe. The contacts are connected to a four-quadrant current voltage source meter which allows for the measurement of the current-voltage characteristics of the solar cell.

Table I: Global solar irradiance distribution in the 400 – 1100 nm spectrum according to the IEC [1, 2].

  Wavelength range (nm) Percentage of total irradiance in the 400 – 1100 wavelength range
1 400 − 500 18.4 %
2 500 − 600 19.9 %
3 600 − 700 18.4 %
4 700 − 800 14.9 %
5 800 − 900 12.5 %
6 900 − 1100 15.9 %


Table II: Definition of solar simulator classifications according to the IEC [2]. The short-term temporal stability refers to the stability of the light source during the measurement of one data set (e.g., the irradiance, current, and voltage) while the long-term instability refers it is related to the time required to take one entire I-V measurement.  

Classification Spectral match to intervals specified in Table I Non-uniformity of irradiance Temporal instability
Short-term instability Long-term instability of irradiance
A 0.75 – 1.25 2 % 0.5 % 2 %
B 0.6 – 1.4 5 % 2 % 5 %
C 0.4 – 2.0 10 % 10 % 10 %


The solar simulator shown in the video below, supplied by the company Wavelabs from Germany, is one of the first that is employing a set of 20+ different colours light emitting diodes (LEDs) to replicate the solar spectrum. This offers some unique advantages compared to single light source simulators.

  • The spectrum of the solar simulator can be changed by changing the relative intensities of the 20+ LEDs and can achieve an unprecedented match to AM1.5G and other spectral standards.
  • Pulse length can be changed to allow for the measurement of high-capacitance solar cells.
  • Fast quantum efficiency measurements can be made for 20+ wavelengths, including light-biasing required for multi-junction solar cells.
  • LEDs have typically very long lifetimes, hence, reduced operating costs (and increased up-time)
  • In-situ measurement of spectral intensity ensuring excellent repeatability.


[1]         IEC 60904-3: Measurement principles for terrestrial with reference spectral irradiance data, 2008.

[2]         IEC 60904-9: Solar simulator performance requirements, Edition 2.0, 2007.