No, the worst case is much, much lower. The problem is that there are two different definitions of efficiency going on here. The 90-100% conversion to electricity means that 90-100% of the absorbed photons are turned into single electrons. This does *not* say that 90-100% of the energy in the original photons is converted to energy in the electrons. In fact, just as in all other solar cell devices, the photons initially create fast moving electrons, converting all of their energy. But most of that kinetic energy is lost to heat before the electrons can be extracted from the device and used to do work.
So, the take-home message is that efficiency can refer to number of converted photons, regardless of how much energy was lost to heat.