Design, CFD Analysis and Fabrication of Solar Flat Plate ...
M.Tech Presentation(Design, Growth & Fabrication of Solar Cell)
-
Upload
ptravishankar-shukla-universityraipur -
Category
Documents
-
view
333 -
download
1
Transcript of M.Tech Presentation(Design, Growth & Fabrication of Solar Cell)
Design, Growth & Fabrication of InxGa1-xN (0 ≤ x ≤ 0.25) Based Solar Cell
Dissertation by
Rajkumar Sahu
Advisor: Mr. Sonachand AdhikariCo-advisor: Dr. Sanjay Tiwari
CSIR-Central Electronics Engineering Research Institute, Pilani , RajasthanSchool of Studies in Electronics & Photonics , Pt. Ravishankar Shukla University, Raipur
May 22, 2014
Rajkumar [email protected]
Rajkumar [email protected]
May 22, 2014Slide 2
Outline1. Motivation & background
• Photovoltaic (PV), High-efficiency, InGaN.
2. Objectives• Status, Research Objective, Approach
3. Theory and modeling• Design, Silvaco-Atlas, Optimization
4. Experimental• Growth & Fabrication
5. Conclusion
Rajkumar [email protected]
May 22, 2014Slide 3
Motivation for PV: Population growth
•Energy Demand -
Rajkumar [email protected]
May 22, 2014Slide 4
Motivation for PV: Energy demand
World marketed energy consumption, 1990 - 2035.(source: Based on data from U.S. Energy Information Administration, 2011)
Rajkumar [email protected]
May 22, 2014Slide 6
Motivation for PV: Global warming
(Source:-IPCC, 31st march 2014)
Rajkumar [email protected]
May 22, 2014Slide 7
Motivation for PV: The Sun
ONE SOLUTION COMES UP EVERY MORNING!
SOLUTION
Rajkumar [email protected]
May 22, 2014Slide 8
What is Photovoltaics (PV)?
Photovoltaics is the DIRECT method……of converting SUNLIGHT into ELECTRICITY…
…using a device known as SOLAR CELL.
Rajkumar [email protected]
May 22, 2014Slide 9
Operation of a solar cell• Working principle of Solar Cell based on Photovoltaic effect.• Photovoltaic effect is generation of Electric power from light.• Single junction solar cell is simply PN junction under illumination of light.
• Operating diode in fourth quadrant generates power.
Rajkumar [email protected]
May 22, 2014Slide 10
Advantages of PVGreen Technology
No combustion/emission, radioactivity, disposal High public acceptance
Infinite ResourceFuel, semiconductor
Flexibility and convenienceGrid connected, stand-alone, modularQuick installation, integration
High-quality output power
Rajkumar [email protected]
May 22, 2014Slide 11
Generations of PV1st Generation…
Bulk Silicon, single junctionMature technology, 93% market shareLimitation: Efficiency ~25%, Si
2nd Generation…Thin films decrease material costsLimitation: Low efficiencies, stability
3rd Generation…High efficiency Lower costHigh output power density
Rajkumar [email protected]
May 22, 2014Slide 12
Efficiency limit in single junction solar cell
Efficiency - 25%Loss mechanisms in a single junction solar cell.
Transmission of low energy photons ~23%.Thermalization of high energy photons ~29%.Junction/Contacts ~14%.Recombination due to material quality ~5%.Other: Curve factor Loss, Shading, Reflection ~5%.
Rajkumar [email protected]
May 22, 2014Slide 13
High efficiency approaches: Tandem solar cell
Solar cells with decreasing band gaps are stacked with greatest band gap on the top.High energy photons are absorbed by top layers decreasing thermalization losses.Low energy photons are transmitted to lower band gap layers.
Concept of a tandem solar cell.
Rajkumar [email protected]
May 22, 2014Slide 14
High efficiency approaches: Quantum-well solar cellProposed by Keith Barnham’s group in 1990.
Multi-Quantum-Well (MQW) system is added to the i-region of a p-i-n solar cell.
Quantum Wells (QW) can absorb photons with energy less than that of the bulk material.
↑Absorption → ↑Current → ↑Efficiency
Concept of quantum well solar cell
Rajkumar [email protected]
May 22, 2014Slide 15
III-Nitride material system
Wide direct-band gapWide direct-band gap High absorptionRadiation hardness High carrier velocities Piezoelectric polarization
Rajkumar [email protected]
May 22, 2014Slide 16
III-Nitride material system - Challenges1. Substrate mismatch with GaN
Substrate Latticemismatch
Thermal expansion
Sapphire 16% -34%SiC 3% +2%ZnO 2% -14%
Si 17% +100%
2. Material Quality
High dislocation density -1010cm2
Low lifetimes and diffusion lengths
3. P-GaN
P-type dopingOhmic contact
Rajkumar [email protected]
May 22, 2014Slide 17
Overview: InGaN solar cell researchLawrence Berkeley National Lab
Proposed full spectrum InGaN solar cells.InGaN/Si tandem (modeling).
Cornell UniversityMaterial growth.
University of HoustonSimulation, material characterization.
Novel Semiconductor Material Lab, ChinaFabricated 2.7-2.8 eV InGaN p-n solar cells 0.43 VOC , FF 57%.
Rajkumar [email protected]
May 22, 2014Slide 19
Research objectives
Develop an accurate modeling tool for III-nitride solar cells.
Optimize MOCVD epitaxial growth of InGaN Eg 2.51 eV
Design & fabricate InGaN solar cells Eg 2.51 eV
Understand loss mechanisms in solar cellsMaterial quality, fabrication issues
Develop robust & efficient fabrication scheme
Rajkumar [email protected]
May 22, 2014Slide 20
ModelingSilvaco-Atlas
PC1D, etc.
Fabricationn & p contact, Current
spreading layer
CharacterizationI-V, TLM
2.4 – 2.9 eVInGaN solar cell
GrowthMOCVD(In-situ
Characterization: GaN Growth)
Research approach
Rajkumar [email protected]
May 22, 2014Slide 22
Modeling of solar cells: Silvaco-AtlasDevice parameter files
Structure, Region, Electrodes, Doping, etc.
Material filesModel, Contact, Interface, Indium(%)
OpticalRefractive index, Absorpotion
Silvaco-AtlasSolar cell simulation program
Simulate two and three-dimensional semiconductor devices.
OutputGraphical (Tony plot)
I-V, band diagram, electron & hole conc., mobility etc.
Rajkumar [email protected]
May 22, 2014Slide 23
Modeling of solar cells: Silvaco-AtlasStep 1: Preliminary modification Step 2: Advance modification
Material filesModels, Contact, Interface,
Indium(%)
OpticalRefractive index, Absorption
Polarization
Rajkumar [email protected]
May 22, 2014Slide 24
Primary design: p-i-n solar cell
p-region ~ 100 nmMaximize absorption in i-region.Provide charge to junction.
n-region ~ 2 µmHole diffusion length ~ 2 µm.
Test material i-region. GaN/InGaN p-i-n solar cell.
Rajkumar [email protected]
May 22, 2014Slide 25
Optimization : p-region
ThicknessOn increasing the p-GaN thickness, generated charge carriers are not separated out instead they start recombining in p-region which results in decrease in the Jsc as shown in fig. (a).
DopingWe also investigated the effect of doping by taking different doping concentration. Results shows that Jsc first increases and then decreases with increase in doping concentration, as shown in fig. (a).
ab
c d
Rajkumar [email protected]
May 22, 2014Slide 26
Preliminary design: i-region thicknessIt can be observed that Jsc increases with increasing i-layer thickness. Since i-layer is low bandgap semiconductor compare to p-GaN, it can absorb the photons of some lesser energy than p-GaN.
There is no significant change in the Fill Factor(FF). However, FF starts to decrease as we increase the thickness because series resistance of the cell also increases with increasing thickness of i-layer
Rajkumar [email protected]
May 22, 2014Slide 27
p-i-n structure with varying Indium Composition
Jsc of the double hetero-junction GaN/InGaN solar cell increases with increase in indium composition till 20%, which contributes to increase in efficiency but beyond this composition Jsc decreases sharply as shown in Figure.
Rajkumar [email protected]
May 22, 2014Slide 29
Preliminary InGaN growthEpitaxy: Emcore MOCVD D-125 rotating disk reactor with short jar configuration.
Material investigated: InGaN: [In] 0 – 25%.
Growth variables:Film thickness: 20 – 100 nmTemperature: 640 – 800°CTMIn: 30 – 250 SCCMTMGa: 15 – 150 SCCM
Rajkumar [email protected]
May 22, 2014Slide 31
MOCVD growth of GaN In-situ Characterization
Simulated reflectance profile for GaN growth with extinction
coefficient of 0.001
Simulated reflectance profile for GaN growth with extinction
coefficient of 0.153
Rajkumar [email protected]
May 22, 2014Slide 32
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000
0
2000
4000
6000
8000
10000
12000
14000
16000
Ref
lect
ion
Time (Sec)
p-i-n Solar Cell
MOCVD growth of GaN template
low temperature nucleation layer growth at 550 oC high temperature GaN growth at 1060 oC, lateral growth, and surface roughening which induce a lightly drop in the reflectance intensityisland coalescence which the amplitude and intensity of oscillations increases, qusi-2D GaN growth (500torr)qusi-2D GaN growth
Rajkumar [email protected]
May 22, 2014Slide 33
MOCVD growth of GaN template
(c) low temperature nucleation layer growth at 550 oC (d) temperature ramp and morphology transformation(e) high temperature GaN growth at 1060 oC, lateral growth, and surface roughening which induce a lightly drop in the reflectance intensity(f) island coalescence which the amplitude and intensity of oscillations increases, qusi-2D GaN growth (500 torr)(g) qusi-2D GaN growth
Rajkumar [email protected]
May 22, 2014Slide 34
Baseline solar cell fabrication
p-type Contact Formation
Current Spreading Layer
n-type Contact Formation
Mesa Etchingp-GaN
i-InGaN
n-GaN
u-GaN buffer layer
Sapphire
InGaN/GaN Epi layer
Rajkumar [email protected]
May 22, 2014Slide 35
Baseline solar cell fabrication
3535
P-type Contact Formation
Current Spreading Layer
n-type Contact Formation
Mesa Etchingp-GaN
i-InGaN
n-GaN
u-GaN buffer layer
Sapphire
InGaN/GaN Epi layer
Rajkumar [email protected]
May 22, 2014Slide 36
Baseline solar cell fabrication
P-type Contact Formation
Current Spreading Layer
n-type Contact Formation
Mesa Etchingp-GaN
i-InGaN
n-GaN
u-GaN buffer layer
Sapphire
InGaN/GaN Epi layer
Ti/Al/Ni/Au
Rajkumar [email protected]
May 22, 2014Slide 37
Baseline solar cell fabrication
P-type Contact Formation
Current Spreading Layer
n-type Contact Formation
Mesa Etchingp-GaN
i-InGaN
n-GaN
u-GaN buffer layer
Sapphire
InGaN/GaN Epi layer Ni/Au
Ti/Al/Ni/Au
Rajkumar [email protected]
May 22, 2014Slide 38
P-type Contact Formation
Current Spreading Layer
n-type Contact Formation
Mesa Etchingp-GaN
i-InGaN
n-GaN
u-GaN buffer layer
Sapphire
InGaN/GaN Epi layer Ni/Au
Ti/Al/Ni/Au
Baseline solar cell fabrication
Rajkumar [email protected]
May 22, 2014Slide 39
p-GaN
MQW active layer
n-GaN
u-GaN buffer layer
Sapphire
Ni/Au
Ti/Al/Ni/Au
Baseline solar cell fabrication
FINAL DEVICE
Mesa etching
n-type contact formation
Current spreading layer
CONTACTING
SCHEMS
Rajkumar [email protected]
May 22, 2014Slide 40
n-contact resistance measurement
Fig. n-contact resistance measurement
-30 -20 -10 0 10 20 30 40 500
5
10
15
20
25
30
35
Mean Linear Fit of Sheet1 Resistance
Res
ista
nce
()
Gap (m)
y-Intercept = 10.46Slope = 0.42
x-Intercept = -24.98
c = 6.53x10-5 cm2
Contact Res. = 5.23 Sheet Res. = 41.87 sq.
Rajkumar [email protected]
May 22, 2014Slide 41
ConclusionIndium Gallium Nitride is a semiconductor material with potential to be used in photovoltaic devices.
Established InGaN as a high-efficiency photovoltaic material.
p-i-n double hetero junction structure is optimized with conventional structure and also effect of indium variation is observed on characteristic parameters.
Rajkumar [email protected]
May 22, 2014Slide 42
ReferencesNeff, H., Semchinova, O., Lima, A., Filimonov, A., Holzhueter, G.,“Photovoltaic properties and technological aspects of In1-xGaxN/Si, Ge(0 < x < 0.6) heterojunction solar cells,” Sol. Energy Mater. Sol. Cells 90, 982-997(2006).Jani, O.et al., “Design and characterization of GaN/InGaN solar cells,” Appl. Phys. Lett. 91, 132117 (2007).Shih-Wei Feng et al., “Theoretical simulations of the effects of the indium content, thickness, and defect density of the i -layer on the performance of p - i - n InGaN single homojunction solar cells ” Appl. Phys. Lett. 108, 093118 (2010).Iulian Gherasoiu et al., “Photovoltaic action from InxGa1-xN p-n junctions with x > 0.2 grown on silicon ” Phys. Status Solidi C 8, No. 7–8, 2466–2468 (2011).
Rajkumar [email protected]
May 22, 2014Slide 43
AcknowledgmentI am thankful to the Director, CSIR-CEERI, Pilani for giving me opportunity to work in this laboratory.
I am thankful to my supervisor Mr. Sonachand Adhikari.
I am also thankful to Dr. C. Dhanvantri (Group Leader-ODG), Dr. S. Pal and Dr. Sumitra Singh for constant encouragement in this work. I also thank all ODG members for their support.
I am thankful to training in-charge Mr. Vinod K. Verma.
Rajkumar [email protected]
May 22, 2014Slide 2Thank You