Nanostructured semiconductors for solar cells...Applications of mesoporous materials Metal powders...
16
Nanostructured semiconductors for solar cells Dr. I. Nandhakumar University of Southampton, UK
Transcript of Nanostructured semiconductors for solar cells...Applications of mesoporous materials Metal powders...
Nanostructured semiconductors for solar cells
Dr. I. Nandhakumar
University of Southampton, UK
Research rationale
• ‘High quality’ nanostructured semiconductors using electroplating methods (e.g. CdTe, ZnO) with novel optical and electrical properties
Mesoporous materials
0.1 1 10 100 1000 nm
Mesoporous materials (2-50 nm)
Surfactants
CH3(CH2)15(OCH2CH2)10OH Hydrophobic tail
Hydrophilic headgroup
Amphiphile self-assembly
T /°C
40
60
30 80 70 40 50 60 Amphiphile concentration /wt%
HI I1
La
V1
Lamellar Hexagonal
Micellar cubic
Micellar
Cubic Ia3d
Mz+
Mz+
electrodeposited!semiconductor film!
LC template
conducting substrate!
Electroplating
Surfactant removal
nanostructured!semiconductor film!
Mz+
Two-step templating
Applications of mesoporous materials
Metal powders
Metal films
Silicas and metal oxides
Polymers
Catalysis
Chemical sieves
Batteries Fuel cells Chemical capacitors
Sensors Semiconductors
solar cells optoelectronic devices
!
!
Phasediagram C16EO8/Cd/Te/water/H2SO4
Polarised Optical Microscopy
Liquid Crystal Template Mesoporous CdTe
Nanoporous CdTe
hexagonal arrangement d-spacing 6 nm
d
• TEM gives direct evidence of a hexagonal array with a d-spacing of 6 nm
end-on view: pore size ~ 3 nm pore-to-pore distance 7 nm
Low-angle XRD
0
50
100
150
200
250
300
350
1 1.5 2 2.5 3 3.5 4 4.5
2θ (degrees)
d100
Inte
nsity
(arb
. uni
ts)
d100
Interchannel spacing = d100 / cos30°
nλ = 2 dhkl sinΘ; λCuKα = 1.54 Å
!CdTe!• d100 = 58 ± 2Å !• 69 Å pore to pore !distance!
• Temp. 25°C
!• 17 domains showing 2 spots • largest domains 3 mm2
Measuring domain sizes by synchrotron SAXS
d100 = 60 Å Pore-to-pore = 70 Å
Optical Data
• Interference fringes => optically flat surfaces • Strong absorption above band gap
100
80
60
40
20
0
Ref
lect
ance
%
1600140012001000800600Wavelength nm
Experiment perpendicular Experiment parallel CdTe RT band gap
Chem. Comm., 12, 1374 (2004)"
ZnO
a
d b
c
a
f d
e
b
c a
a
b
c
d
h
g
f
e
j
i
SEM micrographs of three films electrodeposited at -0.845 V vs. SCE at 50 C The template mixture contained a 45 wt.% solution of 0.1 M zinc nitrate and 55 wt.% Brij®56.
Summary & Conclusions
• high quality semiconductors"• CdTe, PbTe, ZnO, Te….""
• 40 % of all the atoms are at or near a surface:!– Enhanced electronic + optical properties for e.g. solar cells, ultra-fast
photodiodes, non-linear optical elements!"
• Unique 3D nanostructuring"
– Exploration of quantum-size effects"• Bandgap compares welotodiode efficiency 14% to ?? i"
