slides latex master thesis

Outline

Evaluation von Laser-bearbeiteten Si-nanopartikeldunnfilmen fur denEinsatz in der Photovoltaik

Levon Altunyan

Fakultat fur IngenieurwissenschaftenNanostrukturtechnik

Universitat Duisburg-Essen

February 01, 2012

Levon Altunyan Universitat Duisburg-Essen - Fakultat fur Ingenieurwissenschaften, Nanostrukturtechnik

Evaluation von Laser-bearbeiteten Si-nanopartikeldunnfilmen fur den Einsatz in der Photovoltaik

IntroductionExperiments and Results

Type I CellsType II Cells

Summary

Outline

1 IntroductionProblem Description

2 Experiments and ResultsDynamic light scatteringProfilometry“Safe” regions determinationReference Cell I-V Measurements

3 Type I CellsPrimary ObservationsFinal IV-CharacterizationsCrystallinity and Cell BehaviorSEM InvestigationsEDX Considerations

4 Type II CellsConductivity Measurements

5 SummaryConclusionsFuture Work





Summary

Problem Description

BSF for Photovoltaic Cells

Motivation:

Classical solutions - negative impact on cells:Different expansion coefficients of Al and Si.Warping of the cell is observed.Difficulties in subsequent production.Increased probability of breakage.

New materials such as Si-nanoparticles investigated:A non-toxic material.Abundant in the nature.Strongly reduced size.

Suggested Solution:

Spin-coated Si-nanoparticles.Sintered with the Silicon layer.Controlled, brief, local heating.Create highly doped p+-type region.Benefit in cost per watt reduction.





Summary

Dynamic light scatteringProfilometry“Safe” regions determinationReference Cell I-V Measurements

Liquids of Si-nanoparticles:

HWR.

p-doped (boron).

DLS - diameter µ ≈ 100 d.nm; σ ≈ 9d.nm.

5%wt; 10%wt;

Ball milling procedure:

1 Pre-dispersing - YTZ beads (300 µm).

2 15 min. ultrasonic cleaning applied.

3 Main-dispersing - YTZ beads (100 µm).

4 Final filtering - pore size 0, 5µm.

10 100 1000

0

10

20

30

Filtered particles Measurement 3 weeks before rest of curves 45 min 2000 rpm 75 min 3000 rpm

Mea

n Nu

mbe

r [%

]

Size [d.nm]

Conclusions:

Si-nanoparticles keep size characteristics after three weeks have passed.

Milling for 75 min and reaching 3000 rpm (final mixing velocity) - sufficient.

Graph fit - gaussian distribution, mean value µ ≈ 100d .nm., standard deviationσ ≈ 9d .nm.





Summary


Layer Thickness

Si-nanoparticles spun on glass substrate:

Big glass substrate (25× 25mm2).

Across sample seven more or lessparallel scratch lines (A to G)considered.

An average height ofhSiNp = 650nm(±25nm).

Inhomogeneous thickness due tosubstrate size.

Peak in middle due to depositionmethod/speed.

874 0953,0

Thickness [nm]

2,0 637 0716,0795,0874,0

,

1 5

,

m] 400,0

479,0558,0637,0

1 0

1,5

ition

[cm

1,0

y-Po

si

0,5

0,0 0,5 1,0 1,5 2,00,0

P iti [ ]2

x-Position [cm]





Summary


“Safe” regions determination

45

40

45

35[%]

30ensi

ty [

25"Eye" Guidelinese

r Int

e

20

Eye GuidelineOptimal IntensityOptimal Intensity Argon

Las

0 2000 4000 6000 8000 1000015

p y gOptimal Intensity Nitrogen

7

0 2000 4000 6000 8000 10000Scan Velocity [mm/min]

0 - no visible laser illumination;

1 - visible laser illumination/no change of the sample’s surface;

2 - optimal = change to silver like color of the sample’s surface;

3 - slightly scratched layer;

4 - ablation of cell’s layer;

5 - layer is totally removed;





Summary


Reference cell - a semi-ready cell with antireflex coating (SiN), front Ag silver gridcontacts and back Al layer metalization from the company Solland Solar.

Breakdown voltage can be extracted to be Vbr = −8, 5V .Open circuit voltage is Voc = 0, 59V .Short circuit current equals to Isc = −27, 78mA.Power at maximum power point is given as PMPP = 9, 7mW .Fill factor of FF = 59, 21% can be computed.An effective cell efficiency of η = 12, 93% was obtained.

-5 0 5 10 15

-0,10

-0,05

0,00

0,05

0,10

Reference Cell by Solland Solarwith Anti-Reflective Coating and Metal Contacts

Dark

Cur

rent

[A]

Voltage [V]-3 -2 -1 0 1

-0,04

-0,02

0,00

0,02

0,04

0,06

0,08

0,10

0,12

Reference Cell with Anti-reflex Coating and Al BSF;No Si-nano Particles, No Sintering;

Cur

rent

[A]

Voltage [V]

Illuminated Dark

Rs = 5,9 Ω;Rsh = 2060,19 Ω;





Summary


Sample Name In Figure Scan Parameters Nano ParticlesReference a1 No Laser Treatment No

#0110 a2 1x10%100mm/min Yes#11 a3 1x10%100mm/min Yes#05 a4 1x15%100mm/min Yes#08 a5 1x17%100mm/min Yes#17 a6 1x17%100mm/min Yes

#0622062011 a7 1x18%100mm/min Yes#13 a8 1x18%100mm/min Yes#07 a9 1x19%100mm/min Yes

#06 20.06.11 a10 6(continuous ↓↑)x50%10m/min 1x30%100mm/min No





Summary

Primary ObservationsFinal IV-CharacterizationsCrystallinity and Cell BehaviorSEM InvestigationsEDX Considerations

0 5 10 15 20 25 30

20

25

30

35

40a4

a5

a2

a1

a3

a7

a9

a10

a7

a7a8

Fill Factor vs Laser Intensity

FF [%

]

Laser Intensity [%]

a9a6

0 5 10 15 20 25 30

0

1

2

3

4

5

6

7

a5

a4

a5a2a1

a3

a9

a10

a7

a8

η [%

]

Laser Intensity [%]

Cell Efficiency vs Laser Intensity





Summary


-0,9 -0,6 -0,3 0,0 0,3 0,6 0,9-0,04

-0,02

0,00

0,02

0,04

Rs = 9,75 Ω;Rsh = 689,54 Ω;

Cur

rent

[A]

Voltage [V]

Dark Illuminated

Sample #05 from 22.06.20111xscan 15% @ 100mm/min

Solar Cell With Anti-reflective Coating and Ag Front Contacts Grid, DepositedSi-nanoparticles.Iscan = 15% Vscan = 0, 1m/min.Fill Factor FF ≈ 41%.Cell efficiency η = 6, 38%.Low series resistance Rs = 9, 75Ω.High shunt resistance Rsh = 689, 54Ω.Levon Altunyan Universitat Duisburg-Essen - Fakultat fur Ingenieurwissenschaften, Nanostrukturtechnik




Summary


1 grinding of the sample’s edges.

cleaningputting on an adhesive tape on the front side of the sample as protection measure;spin-coating;

2 cleaning the edges with a Cotton Swab rinsed in Ethanol or Acetone;

3 grinding of the sample’s edges;

laser sintering step (Iscan = 15% Vscan = 100mm/min);

4 cleaning the sample’s Si-nanoparticle thin film.





Summary


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170,100,150,200,250,300,350,400,450,500,55

Voc

[V]

Combination [-]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

0,000

-0,005

-0,010

-0,015

-0,020

Average Open Circuit Voltage and Short Circuit Current

Combination [-]

Ιsc[

A]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170,150,200,250,300,350,400,450,500,55

FF [%

]

Combination [-]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

0,00,51,01,52,02,53,0

Average Fill Factor and Corresponding Efficiency

Combination [-]

η [%

]

Figure: Applying Different Cleaning Procedures: a.) Open Circuit Voltage and Short CircuitCurrent; b.) Fill Factor and Corresponding Efficiency;





Summary


Combination Included Optional Steps1 Grinded (Step 01) and Sintered Samples, No Particles Deposited2 Cleaning the Edges With a Cotton Swab Rinsed in Acetone (Step 02)3 Cleaning the Edges With a Cotton Swab Rinsed in Ethanol (Step 02)4 Reference Cell, Grinded Only (Step 01), No Particles Deposited, Not Sintered5 Grinding of the Samples’ Edges, (Step 03)6 Grinding of the Samples’ Edges, (Step 01)7 Cleaning with Acetone the Samples’ Nanoparticle Thin Film, (Step 04)8 Cleaning with Ethanol the Samples’ Nanoparticle Thin Film, (Step 04)





Summary


1 2 3 4 5 6 7 80,000

-0,005

-0,010

-0,015

-0,020

Jsc

[A/c

m2 ]

Combination [-]

1 2 3 4 5 6 7 8

0,00,10,20,30,40,50,6

Combination [-]

Voc

[V]

1 2 3 4 5 6 7 816

18

20

22

24

26

FF [%

]Combination [-]

1 2 3 4 5 6 7 8

0,0

0,5

1,0

1,5

2,0

2,5

Combination [-]

η [%

]

Figure: Applying Different Cleaning Procedures: a.) Open Circuit Voltage and Short CircuitCurrent; b.) Fill Factor and Corresponding Efficiency;





Summary


-3 -2 -1 0 1 2 3-0,06

-0,04

-0,02

0,00

0,02

0,04

0,06Q-tip (Acetton) Sample #05

Cur

rent

[A]

Voltage [V]

Illuminated(1) Dark(1) Illuminated(2) Dark(2) Illuminated(3) Dark(3)

-3 -2 -1 0 1 2 3

-0,040

-0,035

-0,030

-0,025

-0,020

-0,015

-0,010

-0,005

0,000

0,005Q-tip (Acetton) Sample #06

Cur

rent

[A]

Voltage [V]

Illuminated (1) Dark(1) Illuminated(2) Dark(2) Illuminated(3) Dark(3)

Figure: Front Side (Step 2-Cleaning the Edges With a Cotton Swab Rinsed in Acetone, Samples05 and 06)





Summary


Sample 20110901 ‐ 08

Scan unbehandeltScan unbehandelt –hochreflektierend – unbehandelt

100 µm

10 µm 10 µm 10 µm

Figure: Micrograph Sintered Coated Sample, Transition (Untreated-Treated-Untreated) Region





Summary


Highly reflective Non-reflective

10 µm

Difference in color!Difference in color!

Figure: Highly vs. Low Reflective Area Comparison; Semi-ready Solar Cell with Anti-reflexCoating and Pre-deposited Front Side Ag Contacts (Sample No 10, 01.09.2011: 6× preheating,Ipreheat = 50%@Vpreheat = 10m/min; 1 sinter scan, Isintern = 30%@Vsintern = 0, 2m/min)





Summary


Figure: Back Surface of the Solar Cells After Sintering: a.) Type II 21.09.2011; b.) Type I,01.06.2011; c.) Kapton R© foils





Summary


800 1000 1200 14000,01

0,1

1

10

2*10-3*exp-1,59/(κb*T)*10-8 μm2/s

2*10-3*exp-1,6/(κb*T)*10-8 μm2/s

6*10-5*exp-1,15/(κb*T)*10-8 μm2/s Extrapolation of graph

Diff

usio

n C

oeffi

cien

t [μm

2 /s]

Temperature [°C]

Diffusion Coefficient ofSilver in Silicon vs Temperature

[43, 44][45, 46]

[47]

1 µm1 µm

O

NCTi

SiAg Zn

Figure: Possible diffusion of front silver contacts into the n-layer takes place. More importantly,there exists a probability that the front contacts get even further - to the p-layer.





Summary

Conductivity Measurements

-3 -2 -1 0 1 2-0,04

-0,02

0,00

0,02

0,04

0,06

0,08

0,10

0,12

Rs = 18,88 Ω;Rsh = 1204,54 Ω;

15% 1scan with Si-nano Particles

Cur

rent

[A]

Voltage [V]

Dark Illuminated

-3 -2 -1 0 1 2

-0,06

-0,04

-0,02

0,00

0,02

0,04

0,06

0,08

0,10

0,12

Rs = 23,38 Ω;Rsh = 76,21 Ω;

Dark Illuminated

35% 1scan with Si-nano Particles

Cur

rent

[A]

Voltage [V]

15 20 25 30 35 40 450,01

0,1

1

10

100 With Particles - Initial Study from 13.09.2011 With Particles - Samples from 16.09.2011 Without Particles - Samples from 16.09.2011

On-Off Current Ratio - Samples With and Without Nanoparticles

Rat

io [+

1/-1

]

Laser Intensity [%]0 10 20 30 40 50 60 70

0,0

0,5

1,0

1,5

2,0

2,5

3,0

Laser Intensity [%]

Effi

cien

cy [%

]

Efficiency vs Laser Intensity





Summary


25 30 35 40 45 50 5510-4

10-3

10-2Conductivity Total vs Laser Intensity

Con

duct

ivity

[Ω−1

cm−1

]

Laser Intensity [%]

Rtotal

RL

RL

RL

RL

UU

U

Si Wafer

Si-NP

RSi-NP

RWafer

RL RLRL RL

dSiNp

dwafer

Argon N2 Si Si+Np (no laser) Al10-3

10-2

10-1

100

5x105106

Con

duct

ivity

[Ω-1cm

-1]

Parameters

Conductivity of samples treated in Ar, N2,

without laser treatment with Si-NP spincoated only

Comparisson: Al(data from Handbook of Chemistry and Physics 90th ed.)





Summary


Dielectric Constant, Results and Discussion

Results:

Conductivity values (σtotal ≤ 2, 57× 10−3 Scm

) corresponds well to the values given inliterature [2].

Comparable with nanoparticle-coated Si-wafer pieces not treated with an IR-laser(σNoLaser ≤ 3, 52× 10−3 S

cm).

Conductivity of the Si-wafer itself σwafer = 0, 0137 Scm

.

Single scans with low intensities are not sufficient for melting most of the depositedSi-nanoparticles.

Remove native silicon surface oxide (Eg = 9eV [2]) with hydrofluoric acid beforelaser treatment.

Use more scans at higher intensity.





Summary

ConclusionsFuture Work

Summary

Summary

The size and stability of the particles inside the dispersion was determined.

Laser treated semi-ready structures from Solland Solar with (Type I) and withoutantireflective coating (Type II).

The characteristic curves of different treated samples are examined.

Fill Factor of FF = 41%; cell efficiency of around η = 6, 38% (Type I).

Fill Factor of FF = 27%; cell efficiency of around η = 2, 95% (Type II).

SEM measurements are carried out.

Estimation of doping depth to at least hBSF = 5µm is achieved.

Breakdown voltage and breakdown field strength are studied.

An initial work with thin-film Kapton R© foils.





Summary

ConclusionsFuture Work

Proposals for Future Work

More thorough studies of the regions characterized by a highly reflective surface.

Further studies of the correlation between crystallinity size and diode behavior.

Pulsed UV-Laser treatment on Kapton R© foils.



ReferencesAbbreviations

N. BensonNETZ Vollversammlung,Conference at University Duisburg-Essen, 2011

K. LamineRealisierung funktionaler Si-Dunnfilme durch Laserkristalisation vonnanopartikularem Silizium.Bachelor Thesis, 2012




Ag silverAl aluminumB boronBSF back surface fieldEDX energy-dispersive x-rayη solar cell efficiencyFF fill factorHWR hot wall reactorIsc short circuit currentO oxygenP phosphorusPmpp power at maximum power pointRs equivallent parasitic series resistanceRsh equivallent parasitic parallel resistanceSEM scanning electron microscopeSi siliconVoc open circuit voltageZn zinc

:Levon Altunyan Universitat Duisburg-Essen - Fakultat fur Ingenieurwissenschaften, Nanostrukturtechnik


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