mudasir malik

2. TOPIC
INCORPORATION OF
SEMICONDUCTOR OXIDES
IN PHOTOVOLTAIC DEVICES

3. Obectives:
At the end of presentation the learners will be able to
explain about
 Semiconductor oxides
 Working of MOS
 Organic solar cells
 Photocatalysis
 Applications of MOS

4. Semiconductor oxides: ” A semiconductor device (such as a diode or a capacitor) in which a
metallic oxide (such as silicon dioxide) serves as an insulating layer.”
 “The materials with band gap energy< “5ev”are essential to absorbs solar
energy.”
 e.g: ZnO,TIO2 ,Sno ,Sio2

5. INCORPORATION
METHODS:
 There are many methods for incorporation of MOS in
photovoltaic devices.
 Semiconductor oxides incorporated in the form of layers
in photovoltaic devices.
 This method include formation of plurality of prcursor
films of the elemental components and at least one III
component being deposited prior to any precursor film
including the I component.
 The method comprising forming a film supported by a
base subtrate.

6. Contin…..
 In the prescence of VI component converting at least a portion of the III
component of the film from elemental form to a compound form in a III-VI
compound.
 After the step of converting the layers of I-III-VI semiconductor material
supported on the base substrate.

7. Photovoltaics:
Solar energy conversion technologies based on organic semiconductor such
as:
 Dye- sensitized solar cell (DSSCs)
 Organic solar cells(OSCs)

8. Metal oxide semiconductor for OSCc:
 Metal oxide semiconductors (MOSs) for the OSCs can be
p-type and n-type materials, contingent on the position
of the conduction band and valence band.
 For an n-type material, electron transfer from the
LUMO of the acceptor to the conduction band (CB) of
the MOS is the requisite. For a p-type contact material,
the valence band (VB) of the MOS is required to match
the HOMO of the polymer. The wide band gap of the
interface materials also serves as a barrier for carriers
of the other sort, thus improving the carrier selectivity
of the contacts .

10. Zinc oxide as a
photopcatalyst:
 ZnO has a wide band gap (3.2 eV) and the unique electrical
and optoelectronic property has made it a potential
candidate as a photocatalyst.
 Studies have shown that the performance of ZnO under
visible light is much more efficient than TiO2 .
 Though it is highly effective under the influence of UV light
, with suitable physio-chemical modifications or by doping,.
 ZnO can be used as a visible light photocatalyst. Apart
from this, the usage of higher-intensity (500 W) visible light
is found to increase the photocatalytic activity of the ZnO
nanoparticles .
 . ZnO photocatalyst is also found to be better than SnO2,
CdS and ZnS for dye degradation under UV and visible light
.

11. TIO2 as a photocatalyst:
 TiO2 is widely employed as a photocatalyst in dye
wastewater treatment, mainly due to its capability to
generate a highly oxidizing electron–hole pair. Moreover, it
has good chemical stability, non-toxicity, and long-term
photostability.
 Numerous modifications of the structure of TiO2 have been
made to achieve the following:
 (i) decrease the band gap energy to harness the photons
from the visible region;
 (ii) increase the efficiency of electron–hole production;
and
 (iii) augment the absorbency of organic pollutants onto
TiO2 by appropriate surface modifications .

12. Photocatalysis:
 Photocatalysis is the key process that enables
the conversion of solar energy into chemical
energy in the prescence of MOS such as Tio2
.Sno2 ,Zno.
 Photocatalytic reactions are basically a multi-
step process involving oxidation and reduction
reactions .
The photocatalytic processes comprise three
fundamental reaction pathways:
 (1) Photons are absorbed by the photocatalysts
upon illumination from the light source. When

13. (2) The photogenerated carriers (electrons and holes) have the tendency to
recombine on the surface/bulk of the semiconductor.
(3) Finally, the reduction reaction occurs when the photogenerated electrons
interacts with the absorbed molecules on the semiconductor (photocatalysts)
surface.

14. Applications:
 The application of MOSs as electrodes
and interfacial layers in the technologies
that involve photon-assisted
physiochemical processes.
 In photovoltaics, MOSs serve as a
scaffold layer for loading dyes in dye-
sensitized solar cells (DSSCs) as well
as electron and hole transport layers in
DSSCs and organic solar cells (OSC).

15. Coni……
The function of scaffold in DSSCs is to facilitate charge
separation and charge transport.

16. Conclusions:
 To achieve high efficiency and cheaper solar
technology, MOS, which is inexpensive and processable
at low temperature, is preferred without compromising
the light absorption and charge transport
characteristics.
 MOS could effectively enhance the photocatalytic
activity and maintain the long-term photooxidation and
photoreduction-processing sites selectively for greater
efficiency.