Calorimetric separation and determination of conversion losses in solar cells

Modulation (photo)calorimetry was used to study the energy conversion losses in solar cells. A scheme that allows detailed discrimination between the various heat-generating processes that occur in solar cells is outlined. The processes that are separated are Joule losses at the contacts, cooling due to carrier injection across the barrier, heating due to 'sliding down the barrier' of photogenerated carriers, and recombination of the injected carriers in the base. Further information was achieved by measuring separately the thermal waves from the front and the back surfaces of the cell. The measurements were done with amplitude modulation of the illumination, in which case the device drives a variable load, or of the voltage. The methodology is also valid for thin-film devices, even if their thicknesses are much smaller than the thermal diffusion length.