Measurement of Solar Cell Efficiency

The most fundamental of solar cell characterisation techniques is the measurement of cell efficiency. Standardised testing allows the comparison of devices manufactured at different companies and laboratories with different technologies to be compared.
The standards for cell testing are:

  1. Air mass 1.5 spectrum (AM1.5) for terrestrial cells and Air Mass 0 (AM0) for for space cells.
  2. Intensity of 100 mW/cm2 (1 kW/m2, one-sun of illumination)
  3. Cell temperature of 25 °C (not 300 K)
  4. Four point probe to remove the effect of probe/cell contact resistance

Constructing a system that meets all the above criteria simultaneously is difficult and expensive. Most research laboratories have simple custom built testers that only roughly approximate the above conditions. Results that are tested "in-house" are typically quite approximate. Periodically companies and research institutions will send devices with record efficiencies to certified testing laboratories for confirmation. Such efficiencies are published as "confirmed efficiencies" along with the name of the test centre and the testing date (see appendix).

Basic structure of a simple IV tester. The current and voltage are measured separately to overcome contact resistance problems.

In the diagram of the IV tester the electronics are shown as all one unit, however, the voltage and current can be measured separately from the power source. Adjusting the height of the lamps rather than the power to the lamps keep the spectrum constant. However small adjustements to the lamp power is possible without unduly affecting the light spectrum.

IV tester components and Sources of Error

The following pages discuss the individual components of a measurement system and the source of error each component may introduce.