Found this paper which appears to be a study of studies of Energy Payback Time for energy used of various PV materials. It's only four years old, so fairly recent.
http://astro1.panet.utoledo.edu/~rel...nergy_revs.pdf
The chart on the fifth page shows the energy cost for the various materials. Later, payback times are shown. Their conclusions are about the same as in my earlier post of about a one to four year payback depending on the material used. Dozens of references are given if anyone would like to dig deeper.
JJ