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Tel Aviv University | Faculty of Engineering
ISES-2015
1
Contacts Configuration for Novel Photo-Thermionic Solar Cells
Rama Sandovsky
Abraham Kribus School of Mechanical Engineering
Tel Aviv University
Support: Israel Ministry of Energy and Water
Gideon Segev
Yossi Rosenwaks School of Electrical Engineering
Tel Aviv University
Tel Aviv University | Faculty of Engineering
ISES-2015
2
The Race to Solar Electricity
PETE
CSP
PV
Tel Aviv University | Faculty of Engineering
ISES-2015
3
Thermionic Conversion
Load
Cat
ho
de
An
od
e e¯
e¯
Energy
Conduction Band
Valence Band
Fermi
Vacuum
Work Function
Waste heat
Electricity
Heat Input
Emission current density
Tel Aviv University | Faculty of Engineering
ISES-2015
4
Photon-Enhanced Thermionic Emission (PETE)
Cathode Anode
-
Schwede et al, Nature materials 2010
Semiconductor cathode
Tel Aviv University | Faculty of Engineering
ISES-2015
5
Contacts Geometry Front grid (as in PV cells) Shading Recombination
hv hv
Contact
Fraunhofer ISE 2-D model - COMSOL
Potential Electrons
concentration Holes concentration
Generation Recombination
Electrons current density
Holes Current density
Tel Aviv University | Faculty of Engineering
ISES-2015
6
Solution in COMSOL-Multiphysics
Electric Potential [V]
Inputs Cathode and anode parameters (materials, sizes, doping concentrations,..) Operation condition (cathode temperature, sun concentration,..) Contact size (fraction) Voltage
Outputs Current density Potential map Charge carrier concentration Recombination concentration
0
20
40
60
80
0 0.2 0.4 0.6
Cu
rren
t[A
/cm
²]
Voltage[V]
Tc=850 K
Tc=750 K
Tc=550 K
Tel Aviv University | Faculty of Engineering
ISES-2015
7
0
50
100
150
550 650 750 850 950
10% contact Sh
ort
-Cir
cuit
Cu
rren
t [A
/cm
²]
Cathode Temperature [K]
The Temperature Effect
PETE Thermionic
Electrons flow lines:
Electrons recombination At contact
Electrons injection (negative recombination)
Tel Aviv University | Faculty of Engineering
ISES-2015
8
Contact Size Effect: Moderate Temperature
Contact area 0.1% 1.0% 10.0% 100.0%
Cu
rren
t [
No
rmal
ized
]
Small contact = Barrier
Tel Aviv University | Faculty of Engineering
ISES-2015
9
Cu
rren
t [
No
rmal
ized
]
Contact area
0
2
4
6
8
10
12
0.1% 1.0% 10.0% 100.0%
Contact Size Effect: High Temperature
Normalized current > 1 Current > Photogeneration
Tel Aviv University | Faculty of Engineering
ISES-2015
10
0
10
20
30
40
50
500 600 700 800 900 1000
Effi
cien
cy[%
]
Temperature [K]
Efficiency
PETE Thermionic
Smaller contact is better Larger contact is better
Impact of contact size is significant
Tel Aviv University | Faculty of Engineering
ISES-2015
11
Conclusions
Contact size is important
PETE regime: Smaller contact
Thermionic regime: Larger contact
Further work
Validate experimentally
Investigate for other cathode materials