In this paper various applications of axial tensile load, bending load, and rolling loading has
been applied to a Copper Indium Gallium Diselenide (CIGS) Solar Cell to lean how it would affect
the solar cell parameters of: Open circuit voltage (Voc), Short circuit current, (Isc), Maximum power
(Pmax), and Efficiency (EFF), and Fill Factor (FF). These Relationships were found for with three
different experiments.
The first experiment the applies axial tensile stress is to a CIGS solar cell ranging from 0 to
200 psi with various strain rates: 0.0001, 0.001, 0.01, and 0.1 in/sec as well as various relaxation
time: 1min, 5min, and 10 min while the performance of solar cell is measured. The results of this
gave several trends couple pertaining the Voc . The first is that open circuit voltage increases
slightly with increasing stress. The second is the rate of increase (the slope) increases with longer
relaxation times. The second set of trend pertains to the Isc. The first is that short circuit current
generally is larger with larger stress. The second is there seems to be a general increase in the Isc
up to a given threshold of stress. After that threshold the Isc seems to decrease. The threshold stress
varies depending on strain rate and relaxation time.
The second set of experiments consisted of holding a CIGS solar cell in a fixed curved
position while it was in operational use. The radii of the curved cells were: 0.41, 0.20, 0.16, 0.13,
0.11, 0.094, and 0.082 m. The radii were performed for both concave and convex cell curvature.
The trends for this show a slight decrease in all cell parameters with decreasing radii, the exception
being Voc which is not effecting, the convex curvature causing a slightly faster decrease than the
concave. This set of experiments were also processed to find the trends of the single diode model
parameters of series resistance (Rs), shunt resistance (Rsh), dark current (I0), and saturation current
(IL), which agreed with the experimental results.
The second experiment consisted of rolling a CIGS solar cell in tensile (cells towards dowel.)
and compression (cells away from dowel) around a dowel to create internal damage. The diameter
of the dowels decreased. The dowel diameters were: 2. 1.75, 1.25, 1, 0.75, 0.5, and 0.25 inches.
This experiment showed similar trends as the bending one but also had a critical diameter of 1.75
in where beyond that damage much greater.
Finally a parametric study was done in COMSOL Multiphysics® to examine how changes
in the CIGS material properties of electron mobility (EM), electron life time, (EL), hole mobility
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(HM), and Hole life time (HL) effect the cell parameters. The trends are of an exponential manner
that converges to a given value as the material properties increase. When EL, EM, HL are very
small, on the order of 10-4 times smaller than their accepted values, a transient like responses occurs.