1. Characterization of Al-doped Conductive
Layer of ZnO for Thin Film Solar Cell
Presenting by:
Mohammad Shakil Khan
3rd Batch
Exam Roll: 409, Reg. No: HA-297

2. OVERVIEW OF THIS
PRESENTATION
 Objective of the Thesis
 ZnO Layer
 Conductive Layer: AZO
 Methodology: Literature Review
 AZO Preparation: Sol-gel Method
 AZO Preparation Steps
i

3. OVERVIEW OF THIS
PRESENTATION
Experimental Layer Preparation
Glass Substrate
Sample Slide Cleaning
 AZO Solution Preparation
 Magnetic Stirring of the Solution
 Deposition & Spin Coating of the Sample
Slides
 Ageing using Oven
Drying in Ambient Temperature
Annealing for Densification
Preparation Completion ii

4. OVERVIEW OF THIS
PRESENTATION
 AZO Characterization
 Thickness Measurement
• Testing Preparation
- Wet Etching Process
• HNO3 Solution
• Etching the Substrates
• Testing
• Result
• Observation
 Surface Morphology Test
• Testing
• Result
• Observation iii

5. OVERVIEW OF THIS
PRESENTATION
 Hall Effect Measurement
• Testing
• Result
• I-V Curve
• Observation
 Future Work Scope
iv

6. OBJECTIVE OF THIS
THESIS
Observe technology for
improving conductivity by
Al doping on ZnO layer
Observe the layer thickness
and relative characteristical
change in the substrate
Identify dopant material
requirement for
optimization of layer
resistivity
1

7. OBJECTIVE OF THIS
THESIS
Impact of deposition on
a fixed range of
substrates
 Observing affect of
surface roughness
produced at fixed
temperatures
2

8. ZnO LAYER
II-VI compound
semiconductors
Wurtzite Crystal
Structure
Large band gap
(Eg=3.37ev)
 Large excitation
energy of 60 meV
Source:
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&
uact=8&ved=0ahUKEwizu6PsuNTKAhVTj44KHcm6D7wQjhwIBQ&url=http%3A%2F%2
Fpubs.rsc.org%2Fen%2Fcontent%2Farticlehtml%2F2013%2Fdt%2Fc3dt51578h&psig
=AFQjCNFtdQPZyTVEjOzaTVhKcXUeifhc9Q&ust=1454343198573957
3

9. ZnO LAYER
 High optical transmittance
in the visible region
 Blocks 95% of all UV
radiation
 Impurity doped ZnO has
Good transparent
conducting oxide (TCO)
characteristics
 Good electrical conductivity
and low optical loss
Source:
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKE
wizu6PsuNTKAhVTj44KHcm6D7wQjhwIBQ&url=http%3A%2F%2Fpubs.rsc.org%2Fen%2Fcontent%2Farticle
html%2F2013%2Fdt%2Fc3dt51578h&psig=AFQjCNFtdQPZyTVEjOzaTVhKcXUeifhc9Q&ust=145434319857
3957
4

10. CONDUCTIVE LAYER: AZO
 Doped binary compounds, Composed
of Al and Zn, common and
inexpensive materials
 Deposited by sputtering from targets
composed of 2-4% Al metal
incorporated in ZnO
 Electrical conductance, measured as
bulk resistivity or as sheet resistance,
related to deposition properties and
thickness
5
Source:
http://materion.com/ResourceCenter/ProductData/InorganicChemicals/Oxides/AZOTransparent
ConductiveCoating.aspx

11. CONDUCTIVE LAYER: AZO
 Full range of sheet resistance, from < 50 Ω/sq to M Ω/sq,
can be obtained with AZO by varying deposition thickness
and parameters
 No substrate heat is required. Patterning of films by
etching is easier than with ITO films. Weak acids of <1%
concentration (0.2% HNO3 for 2 minutes at 18° C) can be
used
 The refractive indices for reactive magnetron sputtered
AZO at 600 nm wavelength range from 1.90 ± 0.02. Pulsed
DC magnetron sputter deposition of AZO produces an
index ~2.00
6

12. CONDUCTIVE LAYER: AZO
Property of high transmission in the visible region and
useable transmission to IR wavelengths as long as ~12
μm.
In contrast, the more commonly known TCO, ITO,
reflects IR at wavelengths longer than ~2 μm.
Transmittance loss for a 120 nm thick coating on Ge is
<10% out to ~12 μm.
7

13. METHODOLOGY:
LITERATURE REVIEW
 Preparation and characterization of ZnO
thin films deposited by sol-gel spin coating
method
 Thickness changes inversely with
increasing or decreasing chuck
rotation
 Effect of Sol Concentration on Structural
and Optical Behavior of ZnO Thin Films
Prepared by Sol-Gel Spin Coating
 Grain size increases with increase in
molar concentration of the deposited
thin films
8

14. METHODOLOGY:
LITERATURE REVIEW
 Al-doped ZnO via Sol-Gel Spin-coating as a Transparent
Conducting Thin Film
 Crystallite size increases but Electrical resistivity
decreases with increasing Al concentration
 Structural and optical properties of ZnO: Al films prepared
by the sol–gel method
 Increasing Al concentration leads to an amorphous
stage of the film appears higher than 2 wt.% of
concentration
9

15. METHODOLOGY:
LITERATURE REVIEW
 Damp heat stability of AZO transparent electrode and
influence of thin metal film for enhancing the stability
 Mobility decreased with increasing Al concentration
 Low Temperature Sol-Gel Technique For Processing Al-
Doped Zinc Oxide Films
 Each annealing concentration of oxygen increased
and concentration of carbon decreased in the films
10

16. AZO PREPARATION:
SOL-GEL METHOD
 Method for producing solid materials from small molecules
 Conversion of monomers:
 A colloidal solution (sol) that acts as the precursor for an
integrated network
Gel of either discrete particles or network polymers
 Sol (or solution) evolves gradually towards the formation of a
gel-like network containing both a liquid phase and a solid
phase
11

17. AZO PREPARATION:
SOL-GEL METHOD
Sol-gel Method steps:
Hydrolysis
Condensation
Gelation
Ageing
Drying
Densification
12

18. AZO PREPARATION:
SOL-GEL METHOD
13

19. AZO PREPARATION STEPS
14

20. EXPERIMENTAL LAYER
PREPARATION
Glass Substrate: 1’’×1’’
Sample Slide Cleaning: Ultrasonic Bath (USB)
process
 Cleaned by brush with de-ionized water and washed
by methanol as mechanical scrubbing
- Methanol for 10mins
- Acetone for 10mins
- Methanol for 10mins
- De-ionized Water for
10mins
15

21. EXPERIMENTAL LAYER
PREPARATION
 AZO Solution Preparation
 Magnetic Stirring of the Solution:
- 2hour at 60 degree Celsius
- Solution was allowed to aged for 24 hr in room temperature
Elements Role Amount
Zinc acetate dehydrate [Zn(CH3COO)2. 2H2O]
Starting
Material
5.39g
2-methoxy ethanol (CH3OCH2CH2OH) Solvent 46.93g
Mono-ethanol-amine [(HOCH2CH2)NH2] Stabilizer 1.5ml
Aluminum nitrate nonahydrate [Al2(NO3)3.9H2O]
Doping
Material
0.11g
16

22. EXPERIMENTAL LAYER
PREPARATION
Deposition & Spin Coating of the Sample Slides
-Solution: 0.5 ml
- RPM: 3000
- Spin Time: 30 seconds
- Rotation/Sec2: 500
17

23. EXPERIMENTAL LAYER
PREPARATION
Ageing using Oven
- At 300 degree Celsius
- Cycle was done
for 5, 10 & 15 times
- Kept in Oven for 10mins
18

24. EXPERIMENTAL LAYER
PREPARATION
 Drying in Ambient Temperature
- Pre-heating stability gain
- At room temperature
- for 10mins for all substrates
 Annealing for Densification
- Both Air & Vacuum annealing
- Nitrogen purging for Air
annealing
at 500 Degree Celsius
- Vacuum annealing for 1 hour 19

25. EXPERIMENTAL LAYER
PREPARATION
Preparation Completion
- Kept for 24 hours for making samples stable
- AZO substrates are ready for experiment
20

26. AZO
CHARACTERIZATION
 Thickness Measurement
- layer thickness influence the efficiency
- Being too thin affect efficiency and durability, being too thick
can increase cost
- Profilometer is used to measure the surface thickness
 Surface Morphology Test
- Analytical Imaging test
- Test is performed for detecting surface defect and roughness
- Surface Imaging Information: Surface structures & defects
21

27. AZO
CHARACTERIZATION
 Hall Effect Measurement
- Production of a voltage across an electrical
conductor, transverse to an electric current in
the conductor and a magnetic field
perpendicular to the current
- Determining resistivity & conductivity
22

28. THICKNESS
MEASUREMENT
 Testing Preparation
 Wet Etching Process
- Using masking tap in one side
- Weak solution of HNO3
 HNO3 Solution Preparation
- 125ml of De-Ionized (DI) water in beaker
- 0.32ml of HNO3 poured in it
- De-Ionized water upto 500ml
23

29. THICKNESS
MEASUREMENT
 Etching the Substrates
- Kept substrates drenched 10mins in
solution
- Taken up and rinsed by De-Ionized water,
then dried 10mins
- Removed mask and got side etch
24

30. THICKNESS
MEASUREMENT
 Testing
- Stylus Surface Profilometer, Model: Detak-
150 was used
- Layer: 1, 10 & 20 times
AZO solution deposited
25

31. THICKNESS
MEASUREMENT
 Result
- For 1-layer: 504nm
- For 10-layer: 5851.9nm
- For 20-layer: 10311.8nm
 Observation
- Huge improvement in layer thickness with each
deposition
- Each deposition obtained significant improvement in
layer thickness hence increase performance
26

32. THICKNESS
MEASUREMENT
 Observation
0
2000
4000
6000
8000
10000
12000
1-layer 10-layer 20-layer
Thickness(µm)
Layer
Layer Thickness
Improvement trend of layer thickness with deposition 27

33. SURFACE MORPHOLOGY
TEST
 Testing
- Used Stylus Surface Profilometer, Model:
Detak-150
- Observe the surface roughness of the
substrates in particular its adhesion,
microstructure and final topography
28

34. SURFACE MORPHOLOGY
TEST
 Result
The layer roughness are:
 For 1-layer, Ra: 45.3nm
 For 10-layer, Ra: 11545.1nm
 For 20-layer, Ra: 1885.1nm
29

35. SURFACE MORPHOLOGY
TEST
 Observation
 Roughness of surface increased by the number of
layer
 1-deposition the roughness is futile; doesn’t affect
the surface (grain size) at all
 From 1-times to 10-times roughness increases
highly
 From 10-times to 20-times not significantly
 Increasing of doping concentration doesn’t
increase the smoothness after certain layer
deposition
30

36. HALL EFFECT
MEASUREMENT
 Testing
 10 times deposited layer
 Instrument: ECOPIA HMS-3000
31

37. HALL EFFECT
MEASUREMENT
 Result
 Bulk Concentration: -9.675×1010 /cm3
 Mobility: 1.564×103 cm3/VS
 Resistivity: 4.126×104 Ω-cm
 Magneto-Resistance: 2.698×108 Ω
 Sheet Concentration: -6.627×106/cm2
 Conductivity: 2.423×10-5/ Ω-cm
 Average Hall Coefficient: -6.452×107cm3/C
32

38. HALL EFFECT
MEASUREMENT
 I-V Curve
33

39. HALL EFFECT
MEASUREMENT
 Observation
 Hall Coefficient value was measured as -
6.452×107cm3/C
 Negative sign of the Hall coefficient indicates Al-
doped ZnO are n-type
 Conductivity is 2.423×10-5/ Ω-cm means the substrates
has optimized conductivity
 After Vacuum Annealing the resistivity is 4.126×104
Ω-cm
 Indicates post-heat-treatment in a reducing
environment efficiently reduced the electrical
resistivity, affected mainly the oxygen vacancy
concentration
34

40.  Increasing efficiency of Al doped ZnO
will increase efficiency of Thin film
 Need to endeavor:
- Impact of layer deposition on roughness
- Impact of conductivity increase at annealing
temperature variation
- Optimize high efficient grain size doping (i. e.)
material and chemical composition
FUTURE WORK SCOPE
35

41. Thank You

42. Q/A