Environmental Engineering Reference
In-Depth Information
Figure 1.1
The approximate shape of the solar spectrum under AM1.5
condition. The shape of the spectrum before entering the air atmosphere
(AM0condition) is also shown for comparison [1].
1.2 Photovoltaic Effect
In the process of effective PV energy conversion, four basic steps
must bebrought together simultaneously. These are:
(a) Absorption of photons usinga suitablematerial
(b) Creation of charge carriers (electron-hole, or e-h pairs) mainly
by breaking bonds between atoms
(c) Separation of oppositely charged free carriers before their
recombination
(d) Collection or transportation of photo-generated charge carriers
through electrical contacts and their passage through an
external circuit to create useful electric current.
If any of these four processes is hindered or not taking place, the
device will show poor conversion e
ciency, or zero PV activity.
Bringing these four stages together by selecting the right materials
and putting them together in a suitable device structure is a
challenging task. In PV research, this task is twofold — (i) exploring
