When these discussions happen I like to calculate some hard systems numbers since they're rarely in either the literature or the popular science articles. All the power available naturally comes from the sun so we need to know the solar spectrum to start. Conveniently there's an ASTM standard , so let's use that.
Here we're only interested in capturing energy outside the human visible spectrum so only radiation above 750nm is interesting.
Integrating from the spectrum data we find that the absolute maximum power that we can ever get from this system is 464W/m^2 (Compared to 1000W/m^2 without wavelength restriction)
The paper  talks about 4.5% PCE (power conversion efficiency), let's be generous and say they can get to 10% before commercialization which implies 46W/m^2 MAX from these window tints.
Since these films are on the sides of buildings we also can't track the sun. Solar angle varies throughout the day but let's integrate for a south-facing building in North American latitudes and we get a power factor of about 0.5 over the course of a day so we're back at 23W/m^2. of electrical energy from these films.
They're going to have to be exceedingly inexpensive to make this effort worthwhile.
In short, think microwatts.