Photoluminescence Excitation Spectroscopy for In-Line Optical Characterization of Crystalline Solar Cells

Techniques to permit in-line characterization during various stages of solar cell research, development, and manufacturing provide a convenient means for optimizing yield, cost, and efficiency. Photoluminescence measurements are widely used for material characterization. This paper examines photoluminescence excitation spectroscopy (PLE) in which the steady-state photoluminescence is monitored as a function of the wavelength of the incident illumination. The use of PLE for in-line optical characterization of direct bandgap crystalline solar cells is explored. With a novel LED-based setup, we measure the PLE response of a GaAs solar cell. Using drift-diffusion numerical simulations, we evaluate the relation between PLE and EQE measurements, and also compare the PLE measurement with the corresponding EQE measurement in order to establish the correspondence between the two techniques.