Fast and reliable spectral response measurements of PV cells using light emitting diodes

We present a measurement system for absolute differential spectral responsivity of solar cells based on high-powered LED arrays coupled to an optical light guide capable of large area illumination. Two different measurement techniques were developed and tested with the same measurement apparatus on a variety of solar cells. The first method is an individual LED lock-in technique that can be performed over a broad frequency range. The second method is based on synchronous multi-frequency optical excitation, called the Fourier transform (FT) technique, using the LEDs and detection with a spectrum analyzer. A scheme for providing light bias using the LEDs during either measurement scheme is discussed.