Environmental Engineering Reference
In-Depth Information
14
th
May 2004
Dear Dr. Dharmadasa
I have read your papers with interest. Giant photocurrents reported
by you are a matter of serious Physics. A long time ago when we
were working with Cu
2
S/CdS cells, we did observe very high currents
even at low e
ciencies. Our peers were not very happy with our
resultsandthuswehesitatedfrompublishingsuchnumbers.Thegood
argument is that even if we assume total absorption of all the solar
photons and a unit quantum e
ciency generating one electron per
photon, the photocurrent expected will be no more than half of the
highest value you have reported. Yes, graded compositions and thus
band gaps do possibly exist though not in any well defined way. But,
this cannot explain high currents (since total absorption is already
assumed) unless you postulate multi-step absorption processes and
multi-electron excitations. If you are serious about your results, you
should devise experiments to look into such effects.
Iwilldrawtheattentionofourstudentsandcolleaguestoyourresults.
Best Wishes
KL Chopra, Professor Emeritus, IITD.
This kind of positive feedback from senior members of the PV com-
munity should take place in order to encourage rapid development
of this most-needed clean energy production technology. It is clear
from this communication that the reluctance to accept high
J
sc
values has been going on during the past four decades hindering
rapid PV development. A radical change in thinking is required for
the benefit of the PV field!
12.2.4
Graded Bandgap Multi-Layer Structures for
Next-Generation Solar Cells
The reader's attention is drawn again to the new results presented
in chapters 6, 7, and 8 for the positive contribution coming from the
