Microscopic Light-Beam Induced Current Measurement for High … · 2018-01-08 · Microscopic...

© Fraunhofer-Center für Silizium-Photovoltaik CSP

Microscopic Light-Beam Induced Current Measurement for High-Resolution Solar Cell Characterization

Susanne Richter, Stephan Großer, Tabea Luka, Marko Turek, Martina Werner, Christian Hagendorf

Fraunhofer Center for Silicon Photovoltaics CSP Otto-Eißfeldt-St. 12 06120 Halle (Saale) [email protected]

28.09.2016

mailto:[email protected]


Content

Motivation

Principle of µLBIC

Results of new devloped application

Comparison of EBIC and µLBIC measurements

Correlative LBIC measurements from macroscopic to microscopic scale

Conclusion


Motivation

Quality control from module to cell level Non-destructive failure analysis, inline diagnostics on module and cell level

Information of local structural, optical and electrical properties needed

Current systems of electrical characterization on solar cell level limited in spatial resolution

correlation between structural and electrical properties

Separate measurement of 2D photo current images and topography and/or light microscopic images

Non-destructive investigation of degradation mechanism

Alternative method to EBIC

EL


Principle of µLBIC Laser beam absorption generates free

electron–hole pairs, which diffuse to and drift within an electric field photo current is induced

The drift process induces a current for the duration in which carriers travel to their respective sinking nodes, i.e. the junction edges where they recombine with their opposite sign

Scanning measurement of current enables generation of maps related to collection efficiency visualization of electrically active defect

n+-Si

p-Si

p+-Si IµLBIC

+

– front

rear

Laser

Challenge: Establishment of software- and hardware interface

Trilateral cooperation of Zeiss Microscopy, Point electronic and Fraunhofer CSP for µLBIC measurement system


Principle of µLBIC Experimental Setup

Local measurement of light induced (photo) current on µm-scale and correlated visualization of topography

LSM 700 (Zeiss)

DISS 5 Scansystem (Point Electronic)


Principle of µLBIC Experimental Setup

Local measurement of light induced (photo) current on µm-scale and correlated visualization of topography

LSM 700 (Zeiss)

DISS 5 Scansystem (Point Electronic)

Measurement of µLBIC

ISC

LSM Measurement

Triggered: • Line • Frame • Pixel


405 nm

555 nm

639 nm

Physical background - absorption depth

Absorption depth (1/α) corresponds to intensity drop of 1/e (~36%)

Choice of wavelength influences information depth and power density

IR UV visible range

3,3 µm

1,6 µm

0,1 µm

639 555 405

1/α (S i)

[1] Data source: http://pveducation.org/pvcdrom/materials/optical-properties-of-silicon

[1]

Wavelength [µm]

Po

we

r d

en

sity

[W

m- ²

µm

-1]

http://pveducation.org/pvcdrom/materials/optical-properties-of-silicon








Comparison of EBIC and µLBIC measurement

200 µm 200 µm

REM / SE-contrast EBIC

n+-Si

p-Si

p+-Si IEBIC

+

– front

rear

e--beam

µLBIC @405 nm µLBIC @555 nm µLBIC @639 nm

200 µm 200 µm 200 µm

A – optical inactive/shadowed region B – range with good life time

C – electrical volume losses due to grain boundaries D – surface losses due to contaminations

Contrast and current values (in nA range) vary for different wavelengths

Results of EBIC and µLBIC correlate


Standard electrical characterization on cell level

EL on Si solar cell Detail of EL image LBIC measurement on solar cell level (LOANA)

Different methods of electrical chararacterization on solar cell level (EL, LBIC,…)

Spatial resolution of LBIC system (LOANA) >100 µm

Microstructural analys is on µm-scale without sample preparation by µLBIC on the example of light induced degradation (LID) test

5 mm


EL & LBIC detail of solar cell

Standard electrical characterization on cell level before and after LID test

EL & LBIC detail of solar cell - after 19 h LID test

980 nm 980 nm

Carrier life time decreases after LID test

Some grain boundaries appear brighter compared to volume due to different degradation effects

Effects on µm-scale?


Correlative LBIC measurements on µm-scale

500 µm

980 nm

µLBIC @ 555 nm (LSM700 / DISS 5)

LBIC @ 980 nm (LOANA)

Positions of LBIC can be found and remeasured by µLBIC for 405 nm, 555 nm and 639 nm in a higher spatial resolution (< 2,5…5,5 µm)

LBIC (LOANA) uses also higher wavelengths with higher absorption depths

90°


Correlative measurements on µm-scale

200 µm 200 µm

µLBIC @ 639 nm light microscopy topography (height map) topography (3D view)

µLBIC@639 nm (scaled)

Correlation of different material properties:

Electrical characterization by µLBIC

Optical information by light microscopy

Structural/topographic analysis by LSM

nA


µLBIC without and after LID test (neighbor cells)

405 nm 555 nm 639 nm

405 nm 555 nm 639 nm

After 19 h LID test

undegradated

µLBIC measurement with equal parameters on neighbor cells

Comparison of electrical properties for different wavelengths

Data evaluation of photo current values


µLBIC without and after LID test (neighbor cell)

200 µm 200 µm

After 19 h LID test undegradated (neighbor cell)

Analyzed Grain structure in two neighbored cells

Quantitative comparison of electrical properties on µm-scale


Quantitative comparison of µLBIC without & after LID test

0 20 40 60 80 100 120

1000

1100

1200

1300

1400

1500

1600

1700

1800

undegradated

LB

IC c

urr

ent [n

A]

position [a.u.]

line 1

line 2

line 3

line 4

1670

1510

1400

0 20 40 60 80 100 120

1000

1200

1400

1600

1800

after 19 h LID test

LB

IC c

urr

en

t [n

A]

position [a.u.]

line 1

line 2

line 3

1600

1470

nA nA

undegradated (neighbor cell) After 19 h LID test


Conclusion

New developed µLBIC system shows good correlation to EBIC measurements

No sample preparation necessary

No vacuum condition needed

Possibility of measurement of complete solar cells enables defect analysis on µm-scale e.g. for investigation of degradation mechanisms

Quantitative (photo) current values in nA-range

Correlation of different material properties (optical, structural and electrical)


Acknowledgement

Financial support in project „Fidelitas“ Contract no. 0325735C

Grigore Moldovan Uwe Grauel

Jörg Steinbach Stefan Groß Martin Beck Andreas Lutter

Thank you for your attention!

Microscopic Light-Beam Induced Current Measurement for High … · 2018-01-08 · Microscopic...

Documents

Transcript of Microscopic Light-Beam Induced Current Measurement for High … · 2018-01-08 · Microscopic...