Environmental Engineering Reference
In-Depth Information
performed in order to test the existence of this effect in these
devices.Themostrelevanttechniqueisthequantume
ciency(QE)
measurement to test whether there is a collection of current in the
IRregion.TherearetwotypesofQEmeasurementsusedinsolarcell
assessment,externalQEandinternalQE.ExternalQEmeasurements
include the effects of optical losses, such as transmission through
the cell and reflection from the surface. Internal QE refers to the
e
ciency with which photons that are not reflected or transmitted
from the cell can generate collectable charge carriers. Internal QE
is also referred to as incident photon to charge carrier e
ciency
(IPCE), and this is the method used to measure the graded bandgap
multi-layersolar cells.
Figure 8.1 shows the IPCE measurements carried out for two
devices in two different laboratories. Their features are similar, and
the losses at UV and IR ends are due to high doping of the materials
at both front and back of the cell. These issues are described in
chapter 7 and dealt with separately in order to achieve the full
features shown in Fig. 1.16 and increase the performance of the
3mm
2
solarcells.
Figure 8.1
TypicalIPCE%curvesmeasuredfortwo3
×
Notethesharpcut-offwavelengthat
∼
740nmindicatinganullcollectionin
the IR region.
