There are indeed several "new" performance reports about the IAM.
However this measurement is rather difficult to perform with accuracy, and there are high discrepancies between the results of different laboratories.
I can just propose my own theoretical calculations, according to the Fresnel's laws, for a standard flat glass without Anti Reflective dispositives.
File comment: IAM Fresnel calculation taking 2 reflexions into account, compared to ASHRAE parametrization.
Ashrae_Fresnel.png [ 6.92 KiB | Viewed 4720 times ]
I took 2 reflexions into account, i.e. the first Air-glass interface, the reflexion on the bottom of the glass side (against the PV cells), and the secondary refraction from glass to air.
The next contributions are completely negligible.