wp3: power conversion module · 2018-10-02 · wp3 - objectives development of a hybrid...
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Grant agreement 737054 Review Meeting – Bruxelles, 6th February 1
WP3: Power Conversion Module
electrons
photons
Thermionic Photovoltaic
emitter
TPV cellcollector
Micro-spacers
Participants
cooling
system
Hybrid thermionic-photovoltaic converter, by A.Datas. Appl. Phys. Lett. 108, 143503 (2016)
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 2
WP3: Power Conversion Module
n- substrate
n
p
emitter / cathode
TPV cell IR PV generation
A (+)
B (-)
Microspacers vacuum micro-gap ~ 1-3 µm (avoid space charge)
Collector coating very low workfunction < 2 eV transparent
Emitter coating low workfunction ~ 3 eV
Cooling
Heat
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 3
WP3: Power Conversion Module
2-terminal Inverted 3-terminal
p
n
n- substrate(transparent)
n- substrate
n
p
emitter / cathode emitter / cathode
TPV cell
electronhole
photon
holeelectron
photon
A (+) A (+)
B (-) C (+)B (-)
TI anode
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 4
WP3: Power Conversion Module
2-terminal Inverted 3-terminal
A (+)
B (-)
A (+)
C (+)B (-)
thermionic
photovoltaic
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 5
WP3 - Objectives
Development of a hybrid thermionic-photovoltaic (TIPV) module
Fabricate the thermionic (TI) emitter and transparent collector with low work functionmaterials
Develop thermal and electrical insulating micro-spacers for the thermionic inter-electrode gap
Fabricate the thermo-photovoltaic (TPV) cell for efficiently converting the radiationemitted by a body operating in the range 1000-2000 °C
Design and optimize a cooling system for the TIPV module, in order to avoid possibledetrimental effects on the performance of the converter.
Provide a characterization system for quantifying the conversion efficiency of the TPVcell
Provide a characterization system for testing all the TIPV components up to thetargeted TI cathode temperature (2000 °C)
Demonstrate the feasibility of the TIPV proof-of-concept and fabricate TIPV devices, tobe further integrated within the overall AMADEUS technology in WP4
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 6
Gantt chart and activity
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
T1.1 D1.2 D1.4/D1.5 D1.7 D1.10
T1.2 D1.1 D1.3 MS1 D1.6 D1.8 D1.9
T2.1 D2.1 - MS2 D2.2 - MS3
T2.2.1 D2.3
T2.2.2 D2.4
T2.3 D2.5 - MS4
T2.4 D2.6
T2.5 D2.7 - MS5
T3.1.1 D3.1
T3.1.2 D3.6 - MS7
T3.2 D3.5
T3.3.1 D3.7 - MS7
T3.3.2 D3.8
T3.3.3 D3.9 - MS8
T3.4 D3.3
T3.5.1 D3.2 - MS6
T3.5.2 D3.4 D3.12
T3.6 D3.10 - MS9/MS10 D3.11 - MS11
T4.1 D4.1 - MS12
T4.2 D4.2 - MS13
T4.3 D4.3 - MS14
YEAR 1 YEAR2 YEAR3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
T1.1 D1.2 D1.4/D1.5 D1.7 D1.10
T1.2 D1.1 D1.3 MS1 D1.6 D1.8 D1.9
T2.1 D2.1 - MS2 D2.2 - MS3
T2.2.1 D2.3
T2.2.2 D2.4
T2.3 D2.5 - MS4
T2.4 D2.6
T2.5 D2.7 - MS5
T3.1.1 D3.1
T3.1.2 D3.6 - MS7
T3.2 D3.5
T3.3.1 D3.7 - MS7
T3.3.2 D3.8
T3.3.3 D3.9 - MS8
T3.4 D3.3
T3.5.1 D3.2 - MS6
T3.5.2 D3.4 D3.12
T3.6 D3.10 - MS9/MS10 D3.11 - MS11
T4.1 D4.1 - MS12
T4.2 D4.2 - MS13
T4.3 D4.3 - MS14
YEAR 1 YEAR2 YEAR3
TPV cell development
Emitter development
Device characterization
Collector coating
Device cooling
Final PoC
✓ D3.1 - Report on emitter candidates
✓ D3.2 - Upgrade of VTEC
Micro-spacers
Collector + micro-spacers
Upgrade
✓ D3.3 - Optimal design of cooling system✓ D3.4 - First report on advance characterization of TIPV
o D3.5 – D3.8 Recipes for TPV cell, cathode, anode, microspacers
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 7
WP3 – Tasks/subtasks and their development
T3.1 T3.1 Development of the thermionic emitter
T3.2 Development of the TPV cell
T3.5.1 Upgrade of VTEC
T3.4 Cooling system design and optimization
T3.5.2 Characterization of thermionic and photovoltaic devices
T3.1 T3.3 Development of the thermionic collector coatings and microspacers
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 8
WP3 – Development: Task 3.1
Thermionic cathode
Substrate
Emitting layer
T3.1.1 – Selection of emitting materials/Emitter
Substrate: Refractory metals (W, Ta, Mo, Re)Emitting layer: many candidates
LaB6, CeB6, AlN:H, CNx, nanodiamond, perovskites
Characteristics of the substrate:1. high melting point (> 2000 °C)2. large thermal conductivity (> 50 W/mK)3. high thermal stability;4. very low electric resistivity (~10-4 - 10-5 Ω cm)5. coefficient of thermal expansion comparable to thatof the emitting layer
Emitting layers grown by Pulsed Laser Deposition
Characteristics of the emitting layer:1. work function ϕC as low as possible, but at thesame time larger than the anode one ϕA
2. spectrally selective emissivity matched with thePV cell, i.e. high (low) emissivity for wavelengthssmaller (larger) than the wavelength correspondingto the bandgap of the PV cell active material (870nm for GaAs and 1700 nm for InGaAs);3. high melting point4. thermal expansion coefficient comparable tothat of the substrate5. thickness in the range 10-20 nm for satisfyingsuitable optical and electric requirements
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 9
WP3 – Development: Task 3.1
T3.1.2 Development of thermionic emitting layer
Work function determination by UPS
Samples Φ (eV)*
La-B 3.0
Ce-B 3.1
Al-N 2.8
C-N 4.0
*after 30 s of sputtering for removing surface contaminations
Work function determination by thermionic measurements
Richardson-Dushmann fit:J= ART2exp(-Φ/KBT)
Samples A* (A/cm2K2) Φ (eV)J @ 2000 °C
(A/cm2)
La-B 10.14 2.82 3.19
Ce-B 9.63 2.96 1.34
Al-N 77.30 3.19 2.83
C-N 5.47e-5 1.58 0.023
Main chemical-physical properties of the materialsinvestigated by XPS, SEM, and XRD
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 10
WP3 – Development: Task 3.3
T3.3.1 – Development of the collector coatings
BaF2 and BaO deposited by magnetron sputtering:
• BaO films showed a too high workfunction (4.1 - 4.3 eV) due to
oxygen incorporation excess
• Better results with barium fluoride coatings:
Φ = 3.0±0.1 eV for a thickness of 0.15 nm on p-type GaAs
The lowest work function
First objective: to deposit a very thin layer of an alkali-metallic compounds for lowering the work function of GaAs (4.6-4.8 eV for p-type GaAs) down to 1.7 eV
Two possible alternative strategies:• Controlled deposition by e-beam technique for achieving a better composition.• In-situ deposition of Cs and Ba coatings by commercial alkali-metal dispenser is an
on-going activity: it should guarantee lower work function values.
Sub-monolayer(non continuous film)
Sub-monolayer(non continuous film)
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 11
WP3 – Development: Task 3.3
T3.3.2 – Development of micro-spacers
The minimization of the inter-electrode gap leads to preventspace-charge conditions and tomaximize the TI energy conversionefficiency
Defined geometry for mechanical stability and reduction of the contact surface in order to limit heat transport by conductionShape: circular – Size: 5-10 µm-diameter – Pitch: 50-200 µm
Need of vacuum gap at least in therange 1-3 µm, but phenomena ofthermal expansion could occur:risks of electrodes’ contact
Dielectric ceramic microcolums for guaranteeing thermal and electric insulation
Selected materials: Aluminum oxide (Al2O3)and Zirconium oxide( ZrO2)
Optimal emitter-collector gap for thermionic energyconverters, Appl. Phys. Lett. 100, 173904 (2012)
AMADEUS solution: dielectric microspacers
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 12
WP3 – Development: Task 3.2
GaAs
Fabrication of GaAs PV cells
I-V curves
1.4eV525 nm n-GaAs 2e18
5 nm p+ AlAs 8e18
5 nm p+ GaAs 8e18
N++ GaAs substrate
500 nm p++ GaAs 8e18-1e20
5000 nm n+ GaAs 2e17
GaAs (AA06)
30 nm p+ Al0.5Ga0.5As 4e18
900 nm p+ GaAs 2e18
200 nm n+ Al0.33Ga0.67As 1.33e18
Layer structure
2 mm
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 13
WP3 – Development: Task 3.2
InP
Layer structure
I-V curves0.74eV
In0.53Ga0.47As
Fabrication of InGaAs TPV cells
2 mm
70 A/cm2 and 20 W/cm2
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 14
WP3 – Development: Task 3.2
0
5
10
15
20
25
0.00 0.20 0.40 0.60
Cu
rre
nt
De
nsi
ty (
mA
/cm
2)
Voltage (V)
S1 (InGaAs)
S2 (InGaAs)
AA06 (GaAs)
Fabrication of IBC TPV cells
pn
n- substrate
emitter / cathode
10x10 mm2 5x5 mm2 n-contact
p-contact
IBC TPV cell
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 15
WP3 – Development: Task 3.5
T3.5.1 – Upgrade of the characterization system
UHV DN 160 with full metal CF standard
Laser
source
Some fundamental characteristics: Vacuum level ≃10 -8 mbar Capacity to manage 2000 °C without any problem Cooling of the TIPV anode to avoid overheating Deposition of coatings in-situ Possibility to approach the electrodes with 1 µm resolution
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 16
WP3 – Development: Task 3.4
Numerical simulation of a cold copper plate based cooling system of the TIPV anodeconverter – Input delivered by CNR, IONVAC, and UPM
Detailed steady-state 3D CFD model describing the conductive and convective heattransfer process occurring within the TIPV anode/cooling system
Test of two different cooling mediums (H2O+15% glycol ethylene and liquid N2) undera wide range of operating conditions in terms of input thermal heat flux and coolantproperties
Simulation of alternative scenarios to optimize the TIPV anode/cooling system
Test of additional conceptual cooling systems (heat sink, water pipe cooling)
Cooling medium: H2O&15% ethylene glycol
Realistic operating conditions
Extreme operatingconditions Qmax/4
ΔΤ≈18 oC
Tc=5 oC, mc=0.4 kg·s-1
Many results have been obtained from simulations: investigations as a function of several parameters are carefully reported in Deliverable 3.3
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 17
WP3 – Development: Task 3.5
T3.5.2 – Characterization of thermionic and photovoltaic devices
10-10
10-9
10-8
10-7
10-6
10-5
10-4
-10 -8 -6 -4 -2 0 2
Case C
Case B
Case A
Curr
en
t d
ensity (
A/c
m2)
Voltage (V)
T =1260 ± 10 °C
Experiment Cathode / Emitting layer
Anode
case A 8 nm-thick LaB-O (ΦC = 3.26-3.34 eV from UPS)
Gold (Au) anode(ΦA = 5.0-5.1 eV fromUPS)
case B 15-nm-thick CeB-O emitting layer(ΦC = 3.6-3.9 eV from UPS)
p-type GaAs wafer / 40-nm-thick BaF2 coatinganode(ΦA = 3.7 eV from UPS)
case C 15-nm-thick CeB-O emitting layer(ΦC = 3.6-3.9 eV from UPS)
n-type GaAs wafer / 40 nm-thick BaF2 coatinganode(ΦA = 3.8-3.9 eV fromUPS)
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 18
WP3 – Development: Task 3.5
Device efficiency measurement setup
T3.5.2 – Characterization of thermionic and photovoltaic devices
0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Ele
ctr
ic P
ow
er
(wa
tt)
Heat (Watt)
PowerVsH Efficiency
Heatsink
Heat flux sensor
TPV cell
Cu baseplate
Cu baseplate
DBC substrate
PELTIER COOLER
Emitter
Pcool(Tcell)
Q
Pel
T1
T2
V (Q, T1, T2)
Tcell
Pin Pout
el
el
outin
el
PQ
P
PP
P
eloutin PQPP
Energy balance in the TPV cell
Set point (TPV cell temperature)
Preliminary result
power
efficiency
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 19
WP3 – Deliverables
Del. 3.1: Report on the emitter material candidates
Definition of the thermionic cathode: substrate + very thin emitting layer (10-20 nm).
Description of the main characteristics of both substrate and emitting layer:
• Melting point
• Thermal expansion coefficient
• Thermal conductivity
• Thermal stability
• Electrical resistivity
• Work function
• Spectral emissivity
A list of possible candidates for acting as substrate and emitting layer has been established.
A guideline for the development of the thermionic cathode has been traced: first materials tobe investigated as best candidates, found through the discussion (W as substrate,nanostructured borides deposited by pulsed laser deposition as emitting layers), and possiblealternatives (Mo, Ta, and Re as substrates; nitrides, perovskites, and H:diamond as emittinglayer).
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 20
WP3 – Deliverables
Del. 3.2: Upgrade of VTEC
Definition of the heating strategy for reaching a cathode temperature of 2000 °C: heatingsystem by a continous laser diode up to 250 W has been chosen.
Detailed description of the design of the upgrade of VTEC (Vacuum & Temperature ElectronicCharacterization) system: analysis of the materials involved and the geometrical solutionsadopted to respond to the scientific needs
Report of the fabricated components and the system installation in CNR labs.
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 21
WP3 – Deliverables
Del. 3.3: Optimal design of cooling systemAn evaluation of the proposed design (Cold Copper Plate) in V-TEC upgrade has been performed using
defined boundary conditions and input thermal fluxes.
A steady-state 3D CFD model describing the conductive and convective heat transfer process within theTIPV anode/ cooling system has been applied.
In case of water/ethylene at low Tin (5 oC) and high mass flow rate (0.05 kg·s-1) the anode temperaturecan withstand up to 180 W·cm-2, without its upper part exceeding 100 oC – If the PV cell is placed nearthe anode bottom, the system can move towards higher thermal fluxes, up to 250 W·cm-2.
Increasing the heat transfer coefficient results in an increased heat removal from the TIPV anode.However, the velocities inside the tubes are extremely high in this case (almost 40 m/s).
Pressurized liquid nitrogen (at P>5 bar) can be used for input fluxes higher than 300 W·cm-2 –Unexpected boiling should be avoided in the closed tank.
Cooling medium: Liquid NitrogenCooling medium: H2O&15% ethylene glycol Tc=-196.15 oC, mc=0.074 kg·s-1
Tc=40 oC, mc=0.05 kg·s-1
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 22
WP3 – Deliverables
Del. 3.3: Optimal design of cooling system
Use of materials with lower thermal resistance in the TIPV anode system can improve the coolingefficiency of the copper tank
The water pipe cooling system results in improved cooling efficiency compared to the standarddesign for the same coolant mass flow rate
The heat sink with straight fins cooling system has almost the same cooling efficiency with thecopper tank, but its efficiency can be further improved with a higher coolant mass flow rate
Both new conceptual designs should be further investigated in terms of mechanical stability
The possible optimization of the cooling system has been discussed, by highlighting how to improve the present system and by proposing different solutions.
Water pipe cooling system Heat sink with straight fins cooling system
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 23
WP3 – Deliverables
Del. 3.4: First report on advanced characterization of photovoltaic and thermionic devices
Description of the first characterizations of the two single devices: thermionic by the VTECupgrade and TPV by an ad-hoc measurement system for evaluating the conversion efficiency.
Analysis of potential and possible bottlenecks (to be overcome) of the two systems.
Report of the preliminary performance of TI and TPV devices at M12.
Careful review of the future activities and improvements of the advanced characterizations, inthe meantime the final recipes of TI and TPV converters get a mature status.
0 1 2 3 4 5
0.000
0.002
0.004
0.006
0.008
0.010
Outp
ut pow
er
density (
W/c
m2)
Output voltage (V)
Black curve: experimental dataRed curve: hypothesis ΦA = 1 eV
0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Ele
ctr
ic P
ow
er
(wa
tt)
Heat (Watt)
PowerVsH Efficiency
power
efficiency
thermionic thermophotovoltaic
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 24
WP3 – Milestones
Milestone Brief Description Due date Comments
MS6 Critical analysis of the VTEC temperature upgrade
M6
MS7 Cathode & Anode work function (WF)
M15
MS8 Inter-electrode spacers fabrication on anode
M20
MS9 Convergence of thermionictechnologies
M24
MS10 TIPV proof-of-concept M24
MS11 TIPV device for WP4 experiments
M30
The verification was performed. A temperature close to 2000 °C can be
achieved.
At M12: cathode WF close to the target value (2.7 eV); anode WF is still higherthan the expected one (1.7 eV). Risk-
mitigation measures have been proposed.
Preliminary development is satisfying, but it is too early for a definite
evaluation.
Too early for an evaluation.
Too early for an evaluation.
Too early for an evaluation.
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 25
WP3 – Perspectives
Towards the PoC demonstration…
Low cathode and anode work function
Some µm gap required for TI
Transparent anode required for TIPVintegration
Low temperature anode required (for TPVoperations)
After the first year of project, some key-points have to be considered for reaching the goals of WP3and fabricating and demonstrating the TIPV device:
Ensure thermal stability and the suitable operating conditions of all the components for theapplication at 2000 °C
Obtain the condition ΦC› ΦA for a proper operation of the TIPV
Find the optimal design for InGaAs-based TPV anode
Evaluate the behaviour of the TIPV anode with respect to the cooling capacity of the system
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 26
WP3: Power Conversion Module
Participants
Thank you for the attention
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 27
Backup slides?
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 28
T3.2 – TPV cell development
• Semiconductor material growth by MBE
InP
In0.56Ga0.44As
In0.53Ga0.47As
In0.53Ga0.47As In0.56Ga0.44As
Lattice matched Unstrained
Possible defects
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 29
T3.2 – TPV cell development
• Semiconductor material growth by MBE
RHEED calibration of In/Ga ratio growing InAs Quantum Dots on GaAs
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 30
T3.2 – TPV cell development
• Semiconductor material growth by MBE
Bad morphology due to the defects induced by lattice difference between layers
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 31
T3.2 – TPV cell development
• XRD Measurements (very first devices)
Excess of Indium content(~ 3-6 %)
Desired
In0.53Ga0.47As
Obtained
In0.56-0.59Ga0.44-0.41As
Grant agreement 737054 Review Meeting – Bruxelles, 6th February 32
T3.2 – TPV cell development
• InGaAs TPV cell results (very first devices)
The First InGaAs TPV cell
J-V curve
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