Characterisation of Random Pyramid Surfaces Using Laser Scanning

Characterisation of random pyramid surfaces using laser scanning microscopy Dr. Eckard Wefringhaus International Solar Energy Research Center Konstanz e.V.

Overview • Motivation • Methods • Applying different textures • Determination of surface profiles • Definition and determination of topographical parameters • Evaluation of topographical parameter distribution • Results • Parameter distributions • Pertinence of parameters for reflection • Conclusions

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

2

Motivation KOH/IPA and new methods, T, t, c, …

Anisotropic texturing

Performance of solar cells

Surface topography

Light trapping Reflection

Short circuit current, efficiency 16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

(Uniformity of) pyramid height / density / coverage

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

3

Motivation KOH/IPA and new methods, T, t, c, …

Anisotropic texturing

Performance of solar cells

Surface topography

Light trapping Reflection

Short circuit current, efficiency 16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

(Uniformity of) pyramid height / density / coverage

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

4

Motivation Surface topography

(Uniformity of) pyramid height / density / coverage

Up to now, only qualitative statements or very rough classifications - “a more uniform pyramid geometry” [1] - “inhomegenous pyramidal texture with pyramid size 1-6 µm” [2] - “homogeneous collocation of pyramids (base length 2-5 µm)” [3] - “uniform pyramids ( 2-5 µm )” [4] => Define and derive quantitative parameters describing (uniformity of) pyramid height / size / density [1] Vazsonyi et al., Solar Energy Materials & Solar Cells 57, 179-188, 1999. [2] Ximello et al., Proc. 25th EU PVSEC, Valencia, Spain, 1761-1764, 2010. [3] http://www.gpsolar.de/materials/chemikalien/gp-alka-tex-plus/ [4] http://de.rena.com/fileadmin/img/Produkte/200_Solartechnik/230_Batch/232_BatchTex/RENA_DB_monoTex_201011214.pdf

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

5

Methods Applying different textures (by KOH/IPA and other methods) Determination of surface profiles (by confocal laser scanning microscope) Definition and determination of pyramid height and distances (topographical parameters) (by MountainsMaP)

Evaluation of topographical parameter distribution (by EasyFit)

Pertinence of parameters for reflection

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

6

Applying different textures #

pre-cleaning

texture

refl. [%]*

#

pre-cleaning

texture

refl. [%]*

1

as-cut

GP AlkaTex Plus

11,64

11

as-cut

KOH/IPA **

n.d.

2

as-cut

KOH/IPA **

11,37

12

as-cut

KOH/IPA **

n.d.

3

as-cut

KOH/IPA **

11,25

13

as-cut

RENA monoTex

12,31

4

as-cut

KOH/IPA **

11,87

14

as-cut

RENA monoTex

12,61

5

as-cut

KOH/IPA **

11,88

15

as-cut

RENA monoTex

13,81

6

as-cut

KOH/IPA **

11,92

16

as-cut

RENA monoTex

13,16

7

as-cut

KOH/IPA **

11,96

17

O3

KOH/IPA **

13,41

8

as-cut

KOH/IPA **

11,99

18

O3

RENA monoTex

12,31

9

as-cut

KOH/IPA **

11,89

19

SC1

KOH/IPA **

13,69

10

as-cut

KOH/IPA **

11,67

20

SC1

RENA monoTex

12,35

* unweighted mean 400-1100 nm / mean out of 3 measurements; ** different etching times and temperatures

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

7

Determination of surface profiles by LSM

Olympus OLS4000 LEXT

http://www.physics.emory.edu/~weeks/confocal/

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

8

Definition and determination of pyramid height and distances by MountainsMap (x,y,z)-coordinates of pyramid tips

S-filter 0.6 µm [5, 6]

LEXT picture (height layer)

F-filter transformed picture Watershed analysis [5] ISO/DIS 25178-2:2008. Geometrical product specifications (GPS) – surface texture: Areal – Part 2: Terms, definitions and surface texture parameters. [6] ISO/DIS 25178-3:2008. Geometrical product specifications (GPS) – surface texture: Areal – Part 3: Specification operators.

L-filter 100 µm

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

9

Definition and determination of pyramid height and distances by MountainsMap (z)-coordinates of pyramid tips

H1

Z1

(x,y)-coordinates of pyramid tips

H2 CF3

Z2

- pyramid height H (and pyramid base length a(H) = 1.414 H)

- minimum distance to neighbours (minimum pitch, MinP)

- pyramid height Z (and pyramid base length a(Z) = 1.414 Z)

- mean distance to neighbours (pitch, P)

- Coflatness CF 16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

- maximum distance to neighbour (maximum pitch, MaxP)

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

10

Evaluation of parameter distribution by EasyFit 37 bounded, non-negative distributions considered and ranked according to significance: example pitch P (clipping from table) (SoR = sum of ranks, appl. = distribution applicable in n out of 20 cases) distribution

Kolmogorow Smirnow

Anderson Darling

Chi-square

SoR

appl.

mean rank

SoR

appl.

mean rank

SoR

appl.

mean rank

Beta

156

20

7,80

90

20

4,50

138

20

6,90

Chi-Squared (2P)

600

20

30,00

556

20

27,80

510

20

25,50

Fatigue Life (3P)

209

20

10,45

177

20

8,85

170

20

8,50

Gen. Extreme Value

148

20

7,40

142

20

7,10

157

19

8,26

Gen. Gamma (4P)

171

20

8,55

98

20

4,90

142

20

7,10

Gen. Logistic

358

20

17,90

350

20

17,50

334

20

16,70

Johnson SB

58

18

3,22

79

18

4,39

117

16

7,31

Kumaraswamy

256

20

12,80

221

20

11,05

259

20

12,95

16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

11

Results: parameter distributions 0,4

0,14

0,36

Height H: Fatigue life distribution (α, β, γ)

0,32 0,28 0,24 0,2 0,16 0,12

0,1 0,08 0,06 0,04

0,08

0,02

0,04 0

Height Z: Burr distribution (α, β, γ, κ)

0,12

1

2

3

4

0

4

0,11 0,1 0,09 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0

6

8

10

Z [µm]

H [µm]

Coflatness: Johnson SB distribution

(γ, δ, λ, ξ)

2

4

6

8

CF [µm] 16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

12

Results: parameter distributions 0,22 0,2 0,18 0,16 0,14 0,12 0,1 0,08 0,06 0,04 0,02 0

Minimum Pitch: Dagum distribution? (α, β, γ, κ)

1

2

3

4

5

0,12 0,11 0,1 0,09 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0

Pitch: Johnson SB distribution

(γ, δ, λ, ξ)

2

MinP [µm]

4

6

8

P [µm]

0,1

Maximum Pitch: Gen. extreme value distribution (µ, σ, κ)

0,09 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 0

2

4

6

8

10

MaxP [µm] 16. Juni 2011 Dr. Eckard Wefringhaus, ISC Konstanz

Freiberger Forschungsforum 62. Berg- und Hüttenmännischer Tag 2. Fachkolloquium Materialien/Werkstoffe

13

Results: Pertinence of parameters for reflection Partition-Model (all data) - 18 parameters included : H FL (α, β, γ), Z B (α, β, γ, κ), CF JSB (γ, δ, λ, ξ), P JSB (γ, δ, λ, ξ), MaxP EV (µ, σ, κ) - most significant split parameters: MaxP EV σ & H FL β 14 texture KOH/IPA RENA monoTex

Refl. (mean 3) [%]

13,5 13 12,5 12

H FL b=0,17527

H FL b