What is an air mass 1.5 spectrum? [solar cell performance calculations]

The origin of the AM 1.5 spectra, how they are related to actual outdoor spectral distributions, and the implications for outdoor PV (photovoltaic) performance predictions are explained. It is pointed out that the AM 1.5 spectra provide a reference point corresponding to a particular set of atmospheric conditions and a specific air mass. One can expect variations in outdoor PV device performance for different atmospheric conditions and air masses. The uncertainty in using AM 1.5 spectra to predict field performance depends on the particular PV device design and climate. The wavelength distribution of photon flux varies with respect to conditions such as water vapor and air mass, and this in turn influences current densities in PV devices, depending on such device characteristics as bandgap(s). Therefore, PV device design (e.g. optimization) should be based on a range of spectra representing various atmospheric conditions and air masses