F R A U N H O F E R I N S T I T U T E F O R S O L A R E N E R G Y S Y S T E M S I S E

modulum – MODULATED LUMINESCENCE OF SILICON INGOTS, WAFERS AND CELLS

Aiming at steadily reducing the levelized

cost of electricity of PV plants, state-of-

the-art research and development in silicon

photovoltaics must focus on material

quality: This relates to feedstock quality,

to the impact of the crystallization and

wafering processes, and to the impact of

the individual solar cell process on material

quality. Such focus on material quality

calls for accurate analysis techniques of

efficiency-limiting electrical characteristics

in all stages of solar cell production –

ranging from crystallization to metalization.

Luminescence imaging is widely used for

process control by solar cell manufacturers

and their suppliers. Fraunhofer ISE provides

accurate quantitative material and cell

analyses based on harmonically modulated

lifetime and luminescence imaging. With

such process control capabilities, we assist

our customers in meeting the state-of-the-

art challenges in silicon PV research and

development.

The harmonically modulated luminescence

tool ”modulum“ of Fraunhofer ISE

bundles the following capabilities:

n modulated lifetime measurement:

broad range injection-dependent

carrier lifetime

n PL imaging:

2D process control using the latest

hardware, suited for the most versatile

batch measurement applications

n carrier lifetime imaging:

calibrated by harmonically modulated

luminescence, suited for investigations

such as efficiency potential analyses or

interstitial iron imaging

n ingots – wafers – solar cells:

PL and carrier lifetime imaging capability

across the entire solar cell processing

chain

1 Sample of measurement capabilities

from the modulated luminescence tool

”modulum“ of Fraunhofer ISE, combining

software applications like harmonically

modulated lifetime, luminescence imaging,

carrier lifetimeimaging, efficiency

potential analysis (ELBA), and interstitial

iron concentration mapping, as well as

customer-specific applications.

Fraunhofer Institute for

Solar Energy Systems

Heidenhofstrasse 2

79110 Freiburg

Germany

Phone +49 761 4588-0

Silicon Photovoltaics –

Characterization of Process

Materials and Silicon Materials

Dr Martin Schubert

Phone +49 761 4588-5660

Carrier Lifetime Metrology

Dr Johannes Giesecke

Phone +49 761 4588-5560

sipv.characterization@ise.fraunhofer.de

www.ise.fraunhofer.de

06-331-16

1

IRON CONCENTRATION (cm -3)

EFF IC IENCY POTENTIAL (%)BULK L IFET IME (µs )

19

18

17

60

40

20

10 12

10 11

10 10

Applications

The modulum setup and software allows

the following material analyses:

n injection-dependent harmonically

modulated lifetime

n stand-alone PL imaging

n carrier lifetime imaging

n ELBA: efficiency limiting bulk

recombination analysis

n interstitial iron concentration imaging

n ingot bulk lifetime imaging

n individual customer application

Customized Setup

Fraunhofer ISE has more than five years

of experience in providing modulated

luminescence measurement services to the

solar cell industry. With the introduction of

modulum, customers are now able to

deploy this hardware and software them-

selves and customize it to fit their individual

R&D requirements.

The modularity of our concept allows

customers to easily integrate additional

hardware components as well as software

applications and measurement routines.

The modulum tool has already been

successfully integrated into industrial R&D

environments, creating significant added

value. Together with our customers, we

develop appropriate designs for

luminescence-based experiments.

Modulated Luminescence

Harmonically modulated luminescence

infers carrier lifetime from the time shift

between harmonically modulated excess

carrier generation and excess carrier

density. This approach provides several

benefits:

n applicable across the entire solar

cell processing chain – from ingot

to solar cell – with one consistent and

comparable quality control parameter

(carrier lifetime) throughout

n microsecond sensitivity

n weakest impact of trapping

n readily combinable with luminescence

imaging for bulk lifetime imaging of

ingots and wafers, and effective lifetime

imaging of solar cells and metalized cell

precursors

n suited for injection-dependent lifetime

analyses down to lowest measured

excess carrier densities

n dynamic access to carrier lifetime taking

minimal a priori assumptions, yet at a

sharply defined injection level

1 modulum features comprehensive carrier

lifetime measurement capabilities: for silicon

ingots (left), wafers (center) and finished solar

cells (right). The illustration shows carrier life-

time measurements on one substrate from the

ingot state to the finished solar cell.

1

2 Harmonically modulated lifetime, measured

with modulum‘s carrier lifetime calibration.

Modulated excess carrier generation rate [G] and

luminescence intensity [PL] (top) reveal injection-

dependent carrier lifetime [t] (bottom) over a

broad range of excess carrier densities [Dn].

0 3 6 9 12

t / 10-3s

G /

Gm

ax &

PL

/ PL m

ax

1.0

0.5

0.0

G

PL

1012 1013 1014 1015

Dn / cm-3

t / s

10-5

10-4

WAFER BULK L IFET IME (µs )

30

20

10

SOLAR CELL L IFET IME (µs )

10

INGOT BULK L IFET IME (µs )

10

20

30

4020