Curious about Quantum Dots.

[deleted-310044]

Hello,
I have been researching quantum dots. I have come across a few questions that I have not been able to answer and I was hoping you could help with them.

Why are quantum dots so efficient? In theory, if quantum dots work by absorbing a photon and emitting it at a different wavelength, the efficiency should be limited the same way it is limited in solar cells.

Could quantum dots ever emit a photon with a smaller wavelength than the absorbed photon?

Do quantum dots always "glow" or could they act more as a filter, with light passing straight through rather than being diffused in all directions?

Why aren't quantum dot solar cells already on the market? (All I can find is that it's a new technology.)

Thank you very much!