Comment Hot electrons [Re:Perovskite thin films] (Score 3, Informative) 42
I have some amount of skepticism too. Nanosecond lifetimes of hot electrons are amazing, but to date there's no way for turning hot electrons into electrical energy*. So they'd essentially have to invent a technology from scratch.
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Your last sentence... I was just about to post something similar... far as I remember, heat doesn't generate electricity in PV cells... it might even hurt their efficiency, but you beat me to it.
Correct on both, in fact heat decreases efficiency of PV cells (thermal dark current is opposite to photovoltaic current). However, keep in mind that "hot electrons" aren't exactly hot in the sensible-heat sense-- it means that the electrons are in a high-energy state well above the bandgap of the semiconductor. The solar photons come in at an equivalent temperature of 6000K, and all of that energy gets transferred to the minority-carrier electrons, but they quickly shed their excess energy (by transferring energy to the lattice and to other electrons or holes) and relax to the edge of the conduction band (or, ~kT above it). So, using "hot electrons" means somehow finding a way to transfer energy out of the highly-excited initial state immediately after photon absorption, rather than the relaxed quasi-equilibrium state of the conduction band.
So, there's energy there, and in principle it could be used. It's just going to take a new approach to use it. I can't think of a way to do that without adding junctions, and then you end up essentially just re-inventing the multi-junction solar cell.
Now... you could route a water line behind the PV cell, and that'd give you warmer (depends on conditions) water (and might help cool the PV cells which might help their efficiency).
Yes, but of course now you're harvesting the sensible heat, not the hot electrons. This can be useful, if you need low-grade heat.