Why couldn't you collect the solar energy from the outside of the window and put up blinds to block the light from the inside of the window? Putting up blinds won't generate any electricity.
Efficiency is very important but just one-big factor to consider in your application. Less efficient panels can have other benefits that justify their use. Crystalline silicon panels are more efficient than thin film but thin films are lighter and so can be used on roofs that don't support the heavier panels.