When you manage to increase scattering as well as absorption in your nano structure you are in business. Evidently both processes have to occur with higher levels than in a thin film solar cell. Anyhow, the more scattering you can induce in your nano structure PV cell, the more interactions you will get with the radiation absorbing material in your nano structure. Hence, when you manage to increase radiation absorption of your nano structure material so that it has has better absorption characteristics than a thin film structure in a PV cell, you are in business.
Evidently, your nano structure has to be cheaper when you produce it, than a thin film structure or else you will still be out of business. Unless the quantum efficiency of your nano structure panels is much higher than that of of thin film photovoltaic panels.And that's your objective I figger?
According to me these are the physical boundary conditions to be successful with nano structures in PV applications.
Should be a piece of cake for a specialist in nano structures to produce a nano structure according to the boundary conditions I cited.