Environmental Engineering Reference
In-Depth Information
Table 8.1 A summary of device parameters observed for 3
×
3mm
2
solar
cells, when measured individually and two cells connected in series, as a
function of light intensity
×
3mm
2
Cell
×
3mm
2
Cells in Series
Light Intensity
One 3
Two 3
Connected (mWcm
−
2
)
J
sc
(mAcm
-2
)
V
oc
(mV)
J
sc
(mAcm
-2
)
V
oc
(mV)
FF
FF
1.2
980
0.81
0.10
1,960
0.81
0.12
10.5
1,080
0.83
1.20
2,160
0.83
1.26
53.0
1,140
0.85
6.19
2,270
0.85
6.49
100.0
1,150
0.85
12.12
2,310
0.85
12.14
connectedinseriesfurtherconfirmedthisobservationandaddedup
the two
V
oc
values as expected from aseries connection.
8.5.2
I-V Measurements Under Complete Darkness
The above observation of the production of high values for
V
oc
and
FFatthelowestlightintensityguidedtheauthor'sgrouptoperform
I-V characteristics under complete darkness and as a function of
temperature. The devices were mounted inside a metal cryostat,
eliminating background light completely, and the I-V characteristics
were measured as a function of temperature. A typical set of linear-
linear I-V curves observed under complete dark conditions are
shown in Fig. 8.3.
The observation of
J
sc
and the production of
V
oc
values in
the region of 650-850 mV under complete darkness confirms
the PV activity created by thermal energy from the surroundings,
and, hence, the existence of impurity PV activity in these devices.
The variation of
V
oc
and
J
sc
as a function of temperature is as
expected from a PV solar cell.
V
oc
decreases and
J
sc
increases as the
temperature of the device is gradually increased.
In a separate I-V measurement system, diodes were measured
underdarkandilluminatedconditionsforfurtherconfirmation.Two
such plots are shown in Fig. 8.4 in both linear-linear and log-linear
forms. Again, the device exhibits
∼
1,175 mV and
∼
950 mV open
circuit voltage under air-mass 1.5 (AM1.5) and in complete dark
conditions, respectively, re-confirming the PV activity arising from
IR radiation.
