the wide range of semiconductor applications comes from the ability to easily change their conductivity. the addition of even very small amounts of impurities, known as dopants, can change their material conductivity over orders of magnitude even though the impurity concentration might be very small with concentrations of the order of parts per billion. the conductivity may also be changed by applying a voltage or current in one part of the materials to cause a large change in the conductivity in another part of the device. solar cells are usually based around pn junction devices and are just large diodes that have been optimized to absorb light. as such solar cells belong to the family of of bipolar junction devices, which also includes diodes and bipolar junction transistors (bjts).
semiconductors typically use the cgs (centimeter, gram, second) unit system. however, the thickness of a solar cell will be measured in microns. for modeling and calculations, the easiest approach is to convert all dimensions to cm so that a wafer of thickness 160 μm becomes 0.016 cm.