The degradation kinetics of multicrystalline silicon solar cells and wafers at elevated temperature (often termed "LeTID") depend on the specific temperature and injection conditions. We apply different forward biases in the dark at a constant temperature of similar to 75 degrees C to industrial passivated emitter rear contacted (PERC) solar cells fabricated on p-type multicrystalline wafers from a variety of material producers and determine the degradation rate constant in dependence of the excess carrier density at the p-n junction. We find that whereas the specific material properties influence the degradation extent, the degradation rate constant is comparable for all materials but depends on the excess carrier concentration. This implies involvement of one electron in the rate limiting step of LeTID defect formation. The result not only is an important contribution to elucidate the physical mechanism underlying LeTID, but can also be used as a guideline for devising degradation tests of multi crystalline silicon wafers and solar cells.