On Apr 15, 2:45 pm, wrote:
ons why we can't:

Convert light into electricity with 90% efficiency.
We are already doing it, for specialized applications. Internal
quantum efficiencies of certain semiconductor materials have
approached nearly 100% within a narrow spectral range.The challenge is
how to translate that to match the broad solar spectrum. The know-how
exists, but there isn't enough investment to make it happen.

The best efficiency achieved in a lab to date is around 40% of the
total incident energy of the sun's spectrum.

That is why I said 'the challenge is how to translate that to match
the broad solar spectrum'. A narrow band emission can be converted to
electrons with extremely high efficiency. We are already doing it.
Look up the quantum efficiency of any high-end photodetector.

A challenge can be overcome. Fundamental physical limits cannot be
overcome. The quantum efficiencies of todays solar cells are due to
limitations of implementation, not due to a fundamental limit, similar
to the Carnot cycle. If you use a single material (silicon) and a
single junction, it will do poorly with a broad band spectrum,
especially the portion of the spectrum that lays above 1.1um
wavelength.

I can make a 90% efficient solar cell in the lab. Split the solar
radiation into many spectral components, and use a high QE detector
for each spectral range. Make your detectors out of GaN, GaP, AlGaAs,
GaAs, HgCdTe to cover the entire spectrum. That is the crude way to do
it, and will cost enormous $, and will never be practical. But it is
not an impossibility. There is much we can do to improve solar cell
efficiency. The focus needs to be there.