  Energy harvesting from shadow-effect is the generation of electrical power
from a Schottky junction when a part of it is kept in shadow and the remaining
under illumination. It has been recently invented in Au/n-Si junctions, where
modulation of work function of the Au top electrode under contrasting
illumination has been invoked to explain the effect. In this paper, a different
physical mechanism for energy harvesting from shadow-effect in a Schottky
junction is proposed that does not assume change in work function of the top
electrode under illumination. The device, termed shadow-effect energy generator
(SEG), is modelled as two parallel Schottky junction solar cells, one at the
shadowed and the other at the illuminated part, connected with each other in a
closed loop circuit through the Si substrate and the top electrode. To test the
proposed mechanism, ITO/n-Si junction based SEGs have been fabricated. The
values of open circuit voltage in the SEGs have been found to be matching with
the difference of photovoltages of the two cells corrected for the potential
drop across the Si substrate, that validates the proposed mechanism. To further
corroborate the mechanism, the conventional SEG geometry has been modified by
applying a continuous ohmic coating at the back of the Si substrates that
bypasses the resistance of the Si substrate for current flow and results in
higher open circuit voltage and short circuit current. Moreover, ITO/n-Si based
SEGs have been found to produce higher output power density compared to that
reported in Au/n-Si devices in both the conventional and the new geometry.
Although the closed loop present in the equivalent circuit of the SEG devices
lead to wastage of harvested energy, the ITO/n-Si SEG devices can nevertheless
be used as self-powered sensor for light, object and movement detection as well
as for producing electricity from contrasting illumination.
