Infrared active-source lock-in techniques are used for a variety of solar cell inspections, including electro- and photoluminescence,
carrier density imaging, shunt imaging and physical defects. The principles and power of the lock-in
technique are reviewed for these inspection methods. Different camera types, including NIR, MW and LW, are available
for the different techniques. A selection of excitation sources--electrical, laser, lamp and mechanical-stimulate different
physical phenomena. Measurements are presented of several manufacturing yield limiting parameters, and the
advantages and limitations of the techniques are discussed.