Swift Heavy Ion irradiation on Dye Sensitized Solar Cell Dr' Shruti Aggarwal, Associate Professor, G

1
Swift Heavy Ion irradiation on Dye Sensitized
Solar Cell Dr. Shruti Aggarwal,Associate
Professor, GGSIPU
2
Presentation Contains

• 1. Basic understanding of the DSSC.
• 2. About the SHI and experiment.
• 3. Characterization and Results.

3
What are the benefits of DSSc ?
DSSc -easy to be fabricated -low cost -friendly
to the environment -photovoltage is
significantly less sensitive to light
intensity variation than that of conventional
solar cells

• Silicon solar cell
• -costly fabrication process
• -expensive raw materials
• -toxic gases
• -photovoltage is very
• sensitive to light intensity
• variation

4
IThe Understanding of the Device
5
Schematic picture of DSSC
6
Basic Structure
7
ELECTRONIC PROCESSES IN DSSC
How light excites Dye and charge transfer occurs
hv Photon
LUMO
Eelectron
Conduction band
Higher energy
HOMO
Valence band
Dye Black dye Ru (II)
Oxide material TiO2 / ZnO
ITO
8

• Dye molecules absorb incoming light and goes into
  excited state.
• Loses electron to TiO2.
• Electron diffuses to outer electrode.
• Regeneration of dye molecules by taking an e-
  from electrolyte.
• Electrolyte takes up an electron from the counter
  electrode.

9
Equations
10
Light Absorption

• 1. Adsorption of the dye molecules.
• 2. Light absorption

11
Adsorption of the dye molecules.

• Adsorption of dye onto the SC-oxide layer occurs
  via special anchoring group -COOH

12
Charge injection

• No in-build E.field in the TiO2 particles.
• The electrolyte surrounding the particles screens
  any existing E.field and decouples the particles.
  
• E.field only occurs at the SC-electrolyte
  interface H ions

13
Charge injection is due to Energy level
Positioning
14
Rate of charge injection

• Given by Fermi- Golden Rule
• V electronic coupling b/w dye the SC
• ?(E) density of electronic acceptors states in
  CB of the SC

15
Charge Transport

• Electron transport through the SC network.
• Ion transport in the redox electrolyte.

16
Electron transport through the SC network.

• Electron transport is not DRIFT mechanism.
• Electron transport is by DIFFUSION.
• Diffusion of e-s via hopping b/w the electron
  traps in the bulk.

The diffusion coefficients 1 x 10-7 1.5 x
10-5 cm2 s-1
17
Ion transport in the redox electrolyte.

• Regeneration of Dye by the electrolyte
• Reduction of I3- to I- at counter electrode
• It is a 2 e- reaction

18
Recombination

• During electron injection.
• During electron migration in Oxide layer
• a.) loss of e- to oxidized dye
• b.) to a hole in the electrolyte

19
Electron transfer dynamics
20
(No Transcript)
21
Transparent Conducting Oxide Layer (TCO)

• Properties-
• High conductivity/ Low resistivity.
• Optical transmittance in the visible region.
• Reflect IR.
• ITO - In2O3 Sn
• FTO - SnO2 F

22
Indium Tin Oxide (ITO)

• Wide band gap semiconductor 3.75eV.
• To improve the conductivity of In2O3 it is
  doped with Sn.
• The low ? is due to large free carrier density
  generated by -
• 1. Substitution of In by Sn giving out 1
  e-.
• 2. Oxygen vacancies acting as 2 e- donors.
• Charge concentration 1020 1021 / cm3
• Doping level 8- 10

23
PLAN ABOUT DSSC

• Irradiate Photoanode of DSSC by Swift Heavy Ion
  (SHI).
• Then to study the optical and electrical
  properties of photoanode after SHI irradiations.
• Since photoanode of DSSC has three component
• 1. ITO, 2. TiO2 , and 3. Dye
• So, initially we will irradiate each part of
  photoanode by SHI separately and study electrical
  and optical behavior individually.

24
WHAT IS SHI ?

• SHI represents SWIFT HEAVY ION
• It is produced by 15 UD Pelletron at IUAC New
  Delhi.
• We can get different fluences of SHI by changing
  ion charge state, current and time by the
  Pelletron.
• Energy range by Pelletron for SHI is from 30 MeV
  to 325 Mev.

25
IRRADIATION DETAILS
ION --? Ni8
, ENERGY --? 110 MeV , Current 2pnA , Vacuum
10-6 mbar
FLUENCE --? 3 X 10 11 ion/cm2 to 1 X 10 14
ion/cm2 SAMPLE MATERIAL --? ITO
thin film ( 160 nm ) on Corning glass
substrate. Irradiation experiment has been
performed using PELLETRON at IUAC New Delhi,India
Characterizations

• UV-Vis Absorption Spectroscopy

For band gap change

• UV-Transmission Spectroscopy

For transmittance

• AFM

For surface morphology
For confirming the crystal plane

• XRD

For defects near band edge

• Photo Luminescence

Four Probe Transport Measurement
For resitivity/sheet Resistance
26
X-Ray DIFFRACTION
Initially pristine sample has already
stress/strain because its dominant peak for
(222) is different( 30.390 )from the actual value
of 2? ( 30.290 ). When fluence reaches upto
3x1012 ion/cm2 , its peak approaches towards the
highest value of 2? ( 30.620 ), revealing that
strain increases as fluence increases. Peak
again shifted towards lower value of 2? ( 30.420
) beyond the fluence of 3x1012 ion/cm2. It
implies that stress/strain relaxation occures at
higher fluences . SHI irradiation produce heat
which creates oxygen vacancy and it is confirmed
by (400) plane presence in XRD peaks.
Jun S-I, Mcknight TE, Simpson ML, Rack PD. Thin
Solid Films 200547659.
27
AFM
Roghness is lowest and grain formation is also
better for 3x 1012 ion/cm2 fluence, because of
increase in temprature. According to thermal
spike model, ion beam produces heat through out
the track and material get started to melt and
after cooling it makes fine grain. But after
optimized doze, damaged zoan created by ion beam
are overlapped to each other and thus forming the
porous structure and bigger clusters on the
surface. It causes the increase in roughness .
28

PHOTO-LUMINISCENCE PL peak is
observed around 450 nm correspond to the defect
state in ITO. At low fluencess PL quenches,
showing the annealing of defects. At moderate
fluence 3X10 12 ion/cm2, intensity increased and
again decreases with increasing fluence. It may
be due to the creation of radiative center (
point defect ) at 3x1012 ion/cm2. .
29
UV-Vis
Band gap increases from 3.5 eV to 3.79 eV for
pristine sample up to fluence of 3x 1012 ion/cm2.
Transmittance increases from 75 to 83 for this
fluence. Since crystallite size marginally
decreased, so increase in band gap is not due to
quantum confinement. It may perhaps due to
increase in stress/ strain up to 3X1012 ion/cm2
fluence. Beyond this fluence to the highest
fluence band gap slightly decreased ( 3.75 eV ).
It is due to relaxation of the lattice strain
which causes decrease in band gap and hence
transmittance. It is also supported by XRD
spectra as small broadenning and shifting is
observed in peak with fluence.
30
Sheet Resistance Four Probe Measurement
Sheet resistance of ITO increased from 8 to 13
ohm/sq at 3x1012 ion/cm2 fluence while roughness
is the lowest. This resistance is under
acceptable limit of DSSC.
31
CONCLUSION

• 1. Transmittance increased from 75 to 83 at
  3x1012 ion/cm2 fluence. It is very useful
  result in the context of DSSC application. It is
  due to increase in stress/strain in the film.
• 2. Increase in sheet resistance from 8 to 14 ?/?
  at 3x1012 ion/cm2 is under acceptable limit of
  DSSC application.
• PL intensity peak is the highest at 3x1012
  ion/cm2 fluence and before and after this fluence
  peak is low. It may be due to the creation of
  radiative center ( point defects ) at this
  fluence.
• Stress/strain of pristine sample is increasing
  upto 3X1012 ion/cm2 fluence and beyond this
  fluence it again relaxes. It shows that maximum
  stress/strain regarding to film is at this dose.
• Increament in band gap and transmittance pattern
  upto 3X1012 ion/cm2 fluence and beyond this is
  also nearly according stress/strain pattern. It
  reveals that UV-Vis pattern is supported by XRD.

32
200 m2 of STI DSC panels installed in Newcastle
(Australia) the first commercial DSC module
(http//www.sta.com.au/index.htm)
33
Recent Advancements

• Quantum Dots Sensitized Solar Cells

34
Quantum Dots The Sensitizer

• Multiple e-h pairs through impact ionization can
  be achieved, resulting in higher quantum yields.

35
REFRENCE

• 1. M. Gratzel, J. of Sol-Gel Sci. and Tech.,
  Vol. 22, 2001, p. 7.
• 2. M. J. Cass et. Al., J. Phys. Chem. B, Vol.
  107, 2003, p. 113.
• 3. Avasthi DK. Curr Sci 2000 78(11) 1297
• Sunderwaran S, Senthil Kumar O, Ramasamy P,
  Kaviraj D, Avasthi DK and Dhansekaran R, 2005
  Physica B 335 222.
• 5. Vacuum 82 (2008) Deshpandey et,al.
• 6. Jun S-I, Mcknight TE, Simpson ML, Rack PD.
  Thin Solid Films 2005 476 59.

36
Thank You