It means that the electrical current that is created by the solar
cell can now run backwards and partially or fully stop it from working.
In roll-to-roll produced polymer solar cells, for instance, the first
or front electrode is printed as a fine silver grid.
Unfortunately, the ink sometimes contains larger spike-like
silver particles that can protrude through the device.
To minimize this problem, the back electrode was
also printed as a grid structure, so that the
only places where the top and bottom electrode could
meet was at the intersections of these two grids.
The concentration of larger silver particles is still
high enough, so that occasionally, shorts will develop.
In the LBIC images, a very small resistance in a full
short circuit means that the output from the whole cell disappears.
If the resistance is merely decreased somewhat, it affects a smaller area.
This can be seen in the highlighted area of the LBIC image as darker areas in
the vicinity of the grid electrodes, particularly where they meet.
I have invited an expert, Dr. Dieter Karg, from DCG Systems
to talk about lock-in thermography to detect electrical defects in OPV.