Technion, Israel Inst. of Technology

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Technion, Israel Inst. of Technology
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www.ee.technion.ac.il/nano
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Polymer
Calcium/Aluminium
External Circuit
g
l
a
s
s

s
u
b
s
t
r
a
t
e
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Dev 3
Peak Brightness (106cdm-2)
Output Power (mW)
Dev 2
Dev 1
0
200
400
600
Current Density (Acm-2)
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Heterojunction photocells
PPV single-layer diodes show low
photoconductive response. Addition of
electron-accepting layer gives efficient charge
photogeneration.
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M. Granstrom et. al., Nature, 257, 395, 1998
(Laminated Photovoltaic cell)
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Drain
Source
Source
Drain
L
L
W
W
W
W
L
L
SiO
SiO
Insulator
Insulator
2
2
Si
Conductor
Si
Conductor
Vg
Vg
Vg
Vg
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Hopping conduction model

• Conjugated segments ?? States
• Charge conduction ? non coherent hopping

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Hopping conduction model

• Conjugated segments ?? States
• Charge conduction ? non coherent hopping

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There are many layers of complexity!

• Our end goal is to understand organic devices
• We start with a simplified picture
• It is a wide band-gap semiconductor
• It is undoped (in most cases)
• Charge mobility is low

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Reminder (Basics of semiconductor devices, course
044127 )
Intrinsic
N-type
P-type
Metal
EFM
EF
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Isolated Material (?? ?? ?????? ????)
Metal
EFM
Semiconductor
Metal
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Making contact (????? ????? ????)
Metal
EFM
Semiconductor
?? ???? ?????? ??????????
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Making contact (????? ????? ????)
EC
Metal
EFM
EF
Semiconductor
EV
?? ???? ?????? ??????????
????? ?? ??? ????
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Energy levels at equilibrium
EC
EC
EFM
EF
EF
EV
EV
??? ?????? ???? ??? ?? ????? ?????? ??? ?? ???
????? ???? ??????
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?. ?????? ?"? ? ??? ???? ?????
?. ????? ??? ???? ??????? ?? ?????? (?????? ??
???"? ????? ????? ???? ????)
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Isolated Material (?? ?? ?????? ????)
Metal
Semiconductor
?? ???? ?????????
??? ???"? ????? ???????
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Isolated Material (?? ?? ?????? ????)
Connected (????? ????)
"???? ??"
"???? ??" ???? ???? ?? nm
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"???? ??"
???? ??"???? ??" ??? ???? ???? ??????? ???????
??????? ??
????? ????? ??????? Interface dipole
????? ??????? ?????? ?? ????? ?? ????? ????? ???
(????) ?? ?????? (??????)
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?? ???? ???? ?? Heterostructure
Isolated Material (?? ?? ?????? ????)
?? ????? ???????? ?? ????? ?? ??? ??????? ?????
??? ?????? ???? ???? ????
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Energy levels at equilibrium
????? ??? ???? ???? ????? ????
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?? ??? ???? ???? ????? ????????
EC
EFM
EF
EV
????? ?????
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??? ?????? ?? ??? ???? ????
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Energy
Energy
x
x
o
o
Distance,
x
Distance,
x
UBand