Electronic load combination using the NOVA

Electronic load combination using the NOVA
LED Driver
User manual
Please read this manual carefully before starting to use the Autolab LED
Driver kit
The next sections deal with appearance and use of the equipment and contain
necessary information regarding operation and installation.
SAFETY PRACTICES
General
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The following safety practices are intended to ensure safe operation of the
equipment and must be observed during all phases of operation, service
and repair of the instrument.
Failure to follow these instructions may cause unsafe operation.
Metrohm Autolab is not liable for any damage caused by not complying
with the safety requirements.
Failure to follow these instructions may void any warranty provided to this
product.
Electrical hazards
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To avoid electric shock hazard, always ground the equipment by using the
provided power adaptor.
There are no user-serviceable parts. Equipment installation, component
replacement and internal adjustments must be done only by qualified
personnel.
Opening the equipment poses a risk of exposure to potentially dangerous
voltages.
Please also refer to the Electrical Hazards described separately for the
Autolab instrument used.
General precautions
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Use only stable surfaces for setting up the system.
Do not look directly at the light coming out of the light source.
Allow the light source to cool down after prolonged used at high driving
currents.
Autolab LED Driver User Manual
Table of Contents
1 – Scope of delivery ......................................................................................... 6
2 – Hardware requirements ............................................................................... 8
3 – Software requirements ................................................................................ 9
4 – Installation .................................................................................................. 9
4.1 – Autolab LED driver .............................................................................. 10
4.1.1 – Basic connections ...................................................................... 11
4.1.2 – Optional connections ................................................................. 12
4.2 – Autolab LED array ............................................................................... 13
4.3 – Autolab connections for light intensity control .................................... 17
4.3.1 – Connections for constant illumination measurements ................ 18
4.3.2 – Connections for modulated illumination measurements ............. 19
4.3.3 – Optional connections ................................................................. 22
4.4 – Autolab connections to analog outputs ............................................... 27
5 – Software control ....................................................................................... 29
5.1 – Analog control of the light intensity .................................................... 29
5.1.1 – Settings for the DAC 1 input ...................................................... 30
5.1.2 – Settings for the FRA V input....................................................... 34
5.1.3 – Settings for the DIO control ....................................................... 40
6 – Light source calibration ............................................................................. 43
7 – Cell holder ................................................................................................. 46
8 – Experiment description ........................................................................... 48
8.1 – Cell connections .................................................................................. 48
8.2 – DC measurements at constant illumination.......................................... 49
8.2.1 – i/V and power curves at constant illumination............................ 49
8.2.1.1 – Software implementation ............................................... 51
8.2.1.2 – Possible refinements ...................................................... 52
8.3 – AC measurements at constant illumination.......................................... 53
8.3.1 – EIS measurements at constant illumination ................................ 54
8.4 – AC measurements at modulated illumination ...................................... 55
8.4.1 – Intensity modulated photovoltage spectroscopy (IMVS) ............. 55
8.4.1.1 – IMVS measurements ...................................................... 57
8.4.2 – Intensity modulated photocurrent spectroscopy (IMPS).............. 63
8.4.2.1 – IMPS measurements....................................................... 64
8.5 – Safety settings when measurement is aborted ..................................... 71
9 – Thermal considerations ............................................................................. 74
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Autolab LED Driver User Manual
Autolab PGSTAT in combination with LED Driver
The characterization of optical energy conversion devices (i.e. solar cells) requires
controlled illumination from a light source. Depending on the experimental
requirements, the light source can be a solar simulator, a simple LED, or a laser.
This light source must be programmable in order to expose the device under test
(DUT) to a user-defined light intensity. The type of light profile depends on the
experimental conditions.
Information
This document provides basic information regarding the Autolab LED Driver and
the associated products. This kit is controlled through the NOVA software.
Additional resources are available online (www.metrohm-autolab.com/support).
This manual describes the use of the Autolab LED Driver and LED light source in
combination with the Autolab PGSTAT.
Note
The LED Driver is compatible with all Autolab PGSTAT instruments except the
Autolab PGSTAT302F. In this manual, the term Autolab is used to describe any
type of compatible instrument.
The following measurement techniques are possible with the LED Driver in
combination with the Autolab PGSTAT:
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Polarization curves and power density curves
Charge extraction measurements
Electrochemical impedance spectroscopy at constant illumination
Intensity-modulated photovoltage spectroscopy (IMVS)
Intensity-modulated photocurrent spectroscopy (IMPS)
It is also possible to combine all the measurement techniques in a single
experiment.
Warning
This device must be used carefully to prevent personal injury. Metrohm Autolab
is not responsible for physical injuries sustained while using this product. It is
advised to read this documentation very carefully before operating this
equipment. Please contact Metrohm Autolab ([email protected]) in
case of problems.
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Autolab LED Driver User Manual
Whenever applicable, a hot surface warning label or strong optical radiation
warning label are used in this manual as reminder to the hazards that can be
encountered when operating this equipment.
Warning
This warning symbol is used in this document to indicate a hot surface hazard
related to the heat dissipation in the light source. Allow the system to cool
down after prolonged use.
Warning
This warning symbol is used in this document to indicate an optical hazard
related to highly focused beam of light generated by the LED light source. Do
not look directly into the light beam when the light source is on.
1 – Scope of delivery
The LED Driver kit is supplied with the following items:
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Autolab LED Driver box
Power adaptor
50 Ω terminator plug
6 BNC to SMB adaptor plugs
3 SMB shielded cables (1 m)
1 BNC shielded cable (1 m)
1 BNC shielded cable (2 m)
2 BNC shielded cable (50 cm)
DIO to BNC cable for Autolab N series PGSTAT instruments and µAutolab
DIO to BNC cable for Autolab PGSTAT101 and M101 module
Optical bench
The LED Driver kit is intended to be used with the Autolab LED light source,
included with the LED Driver:
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1 LED array cover (627 nm), 700 mA maximum current
1 LED cover holder
1 LED cover holder connection cable (2 m)
1 calibrated photodiode holder with calibration certificate
Additional accessories are available for the Autolab LED light source:
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Additional LED covers (see Section 4.2 for more information)
Additional LED cover holders
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Autolab LED Driver User Manual
Figure 1 shows a complete overview of the LED Driver kit items.
Figure 1 – The LED Driver kit, including optical bench, light source and photodiode holder
The three SMB/SMB shielded cables can be fitted with SMB to BNC adaptor plugs.
Depending on the type of FRA module used in combination with the LED Driver,
these cables can be modified accordingly:
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For the FRA2 module, the cables must be fitted with SMB to BNC adaptors
on both ends (see Figure 2).
Figure 2 – Configuration of the SMB cables used in combination with the FRA2 module
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For the FRA32M module, the cables must be fitted with SMB to BNC
adaptors on a single end (see Figure 3).
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Autolab LED Driver User Manual
Figure 3 - Configuration of the SMB cables used in combination with the FRA32M module
2 – Hardware requirements
The experimental setups described in this manual require the following hardware:
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Autolab PGSTAT, µAutolab 1 or Multi Autolab (for DC measurements)
FRA2 or FRA32M module (for AC measurements)
Autolab LED Driver
Autolab LED cover with holder
Warning
The LED Driver has a working range of 0-10 V, which means that the FRA2
modules must be modified to the 0-10 V input range. The hardware setup must
be adjusted accordingly (see Appendix 1).
1
The µAutolab can only be used for DC measurements.
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Autolab LED Driver User Manual
3 – Software requirements
The experimental setups described in this manual require the following software:
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Latest version of NOVA
This manual assumes that the reader is familiar with the operation of the Autolab
instrument in combination with the NOVA software. More information on the
software tools used in this manual can be found in the following document,
available from the Help – Tutorials menu in NOVA:
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Autolab control tutorial
External devices tutorial
Impedance spectroscopy tutorial
NOVA Getting started
NOVA User manual
Command list
4 – Installation
This section describes the required connections between the Autolab PGSTAT and
the Autolab LED driver.
The combination of the PGSTAT with a LED driver is a very useful hardware
construction which allows measurements at controlled light intensity on solar
cells. In this setup, the LED Driver is used to control the output of the light source
while the Autolab PGSTAT is used to measure the potential and current on the
device under test (DUT).
The LED Driver can be operated in constant output mode or in modulated output
(which requires the FRA2 or FRA32M module). The Autolab PGSTAT can be
operated in potentiostatic mode or in galvanostatic mode.
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Autolab LED Driver User Manual
4.1 – Autolab LED driver
The Autolab LED driver is an analog and digitally programmable constant current
source which can be used to supply a driving current to a LED or a LED array (see
Figure 4). The maximum driving current which can be generated by the LED driver
is 1000 mA DC.
Figure 4 – Top view of the Autolab LED driver
The LED driver provides the following functionality:
1. A dual analog programmable input ( FRA V and  DAC 1) for direct
control of the LED current supplied by the driver.
2. A current to voltage converter for direct analog readout of the driving
current (FRA Y ).
3. A dual input feedthrough for the Autolab Eout and iout signals to the
FRA  X output. The input is controlled by a DIO triggered switch ( DIO
input).
The LED Driver is designed to control a dedicated LED array of three, 1000 mA
rated LEDs, provided by Metrohm Autolab (see Section 4.2 for more information).
This light source is recommended for this application and will be assumed in the
rest of the document.
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Note
The light source is a critical component of this hardware setup and it should be
chosen carefully. Light sources like LEDs are economical and offer a narrow
spectral distribution. Laser diodes can also be used. Both light sources have a
low power output. Alternative light sources can be used however their use fall
outside of the scope of this manual.
When working in combination with the FRA2 or FRA32M module, the maximum
frequency that can be used in combination with the LED driver is 20 kHz. The
maximum frequency is limited by the voltage-to-current converter in the LED
driver.
4.1.1 – Basic connections
Figure 5 shows an overview of the basic connections to and from the LED driver.
All the connectors located on the left-hand side of the driver are input connections
from the Autolab PGSTAT to the LED driver. The BNC connectors located on the
right-hand side of the driver are the output connections to the Autolab PGSTAT.
Figure 5 – Overview of the basic connections provided by the LED driver
The following connections are located on the left-hand side:
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FRA V input ( FRA V): this input is used to supply the AC amplitude used
to modulate the light intensity, in volts (0-10 V input range). See Section
4.3.2 for more information. When no signal is supplied to this input, this
plug must be shorted using a 50 Ohm termination plug (included).
DAC164 #1 input ( DAC 1): this input is used to supply the DC
amplitude used to modulate the light intensity, in volts (0-10 V input
range). See section 4.3.1 for more information. This value must always be
larger than the value supplied to the FRA V input.
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The following basic connections are located on the right-hand side:
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LED power ( ): this connector is used to provide current to the LEDs
through a dedicated cable. This cable is used to interface the driver and the
holder described in Section 4.2.
ELED output (DYN V ): this output provides a voltage (0-10 V),
corresponding to the difference between the value provided to the DAC1
input and the value provided to the FRA V input (on the left-hand side of
the driver).
i LED output (FRA Y ): this output provides a voltage (0-1 V), proportional
to the LED current. The output value, in mV, corresponds to the driving
current, in mA (1000 mV  1000 mA driving current). For IMPS and IMVS
measurements, this output is fed into the FRA Y input.
18 V input: this input is used to supply power the LED driver. The driver is
powered when the power status LED located next to this input is lit.
4.1.2 – Optional connections
Figure 6 shows an overview of the optional connections to and from the LED
driver (the basic connections are grayed out). All the connectors located on the
left-hand side of the driver are input connections from the Autolab PGSTAT to the
LED driver. The BNC connectors located on the right-hand side of the driver are
the output connections to the Autolab PGSTAT.
Figure 6 – Overview of the optional connections provided on the LED Driver
(Basic connections are greyed out)
The following connections are located on the left-hand side:
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DIO input ( DIO): this input can be used to connect to the DIO port(s) of
the Autolab. By setting the DIO to the down status (default) or the up
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Autolab LED Driver User Manual
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status, the switch connected to the Eout and iout can be toggled 2. The default
position is set to iout.
Eout input ( E out): this input can be used to connect to the Eout plug
provided by the monitor cable of the Autolab (see Section 8.4.1 for more
information). The Eout signal is required during IMVS measurements.
i out input ( i out): this input can be used to connect to the iout plug
provided by the monitor cable of the Autolab (see Section 8.4.2 for more
information). The iout signal is required during IMPS measurements.
The following optional connections are located on the right-hand side:
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Eout/i out output (FRA X ): this connector provides a direct connection to
either the Eout or the iout supplied on the left-hand side of the driver,
through the Eout and iout connectors, respectively. The default is iout
(indicated by the status LED). This output is connected to the FRA X for
IMPS (iout) or IMVS (Eout) measurements.
4.2 – Autolab LED array
The Autolab LED driver can be connected to a dedicated LED array. This array
consists of a tri-focal LED assembly, collimated into a narrow beam with a lens.
The LED array and the lens are enclosed in an anodized aluminium cover
(see Figure 7).
The light beam width is 18°.
Warning
The lens mounted on the light source provided a highly focused beam of light.
Do not look directly into the light source when it is operating, even if the
driving current is small.
The switch can also be toggled through an analog voltage. Supplying more than 2.5 V on this
DIO input triggers the switch.
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Autolab LED Driver User Manual
Figure 7 – Schematic top view of the LED array casing
The factory default cover, supplied with the kit, is fitted with three, 700 mA rated,
red LEDs (wavelength: 627 nm).
Other covers are available, on request. The following wavelengths are available
(see Table 1):
Article code
Color
Wavelength (nm)
Maximum output (Lumen)
LDC655
Deep Red
655
n.a. 3
LDC627
Red
627
306
LDC617
Red-Orange
617
366
LDC590
Amber
590
396
LDC530
Green
530
390
LDC505
Cyan
505
360
LDC470
Blue
470
174
LDCCW
White (Cool)
n.a.
540
LDCWW
White (Warm)
n.a.
690
LDCNW
White (Neutral)
n.a.
330
Table 1 – Overview of the available LED covers
The back plane of the LED cover is fitted with two holes used to provide electrical
contact to the LEDs enclosed in the cover (see Figure 8). Three screws are
embedded into the cover to fasten it to the holder.
The output in Lumen for the Deep Red source is not specified. The maximum output power is
1740 mW at 700 mA driving current.
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Autolab LED Driver User Manual
Figure 8 – Schematic bottom view of the LED array casing
A label is located on the back of the cover, indicating the type of LED included in
the cover.
The cover can be mounted on a dedicated holder (see Figure 9). The holder is
fitted with two spring mounted pogo pins that are intended to provide the
electrical contact to the LEDs through the matching holes located in the back
plane of the cover.
Figure 9 – The LED cover and the holder
To attach the cover to the holder, align the pogo pins with the matching holes in
the back plane of the cover. The three screws located in the cover can be used to
tighten the cover onto the holder.
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Autolab LED Driver User Manual
Note
When tightening these screws, do not tighten one screw at a time but alternate
between both screws in order to distribute the traction on each screw evenly.
Do not over tighten the screws.
No soldering is required. Connecting the LEDs through pogo pins allows for a
quick change of the wavelength of the light source, by simply replacing one cover
by another.
Warning
Do not exchange the LED cover while the driver is in operation. Always power
off the LED Driver before exchanging the LED cover.
The LED cover and the holder are fitted with six radial cooling fins, which allow
evacuation of the heat generated by the light source. The higher the light intensity
or the driving current supplied to the LEDs by the LED driver, the hotter the holder
becomes (see Figure 10).
Figure 10 – Surface temperature of the LED cover in function of the driving current, in mA
(measured with a 590 nm Amber LED cover, settling time: 60 s)
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Warning
When the light source is driven at high currents, the cooling fins can get very
hot (up to 60 °C). Do not touch these fins and allow for enough cooling time to
prevent injury.
Figure 11 shows the cover attached to the holder.
Figure 11 – The complete LED cover holder
4.3 – Autolab connections for light intensity control
Depending on the experimental setup, two connection schemes are possible
between the LED driver and the Autolab:
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Measurements at constant light illumination: these measurements are
performed with the LED driver set to a fixed user-defined light intensity.
The light source intensity can be changed during the experiment, but no
additional modulation is used. For this setup, only the DAC 1 input of the
driver is used. The  FRA V input must be shorted by a 50 Ohm
terminator plug (see Section 4.3.1 for more information).
Measurements at modulated light illumination: these measurements are
performed with the LED driver set to a fixed user-defined light intensity
with an additional low amplitude intensity modulation. For these
measurements, the DAC 1 and FRA V inputs are both connected to the
Autolab while the Eout, iout and DIO inputs can be connected to the
Autolab, if necessary (see Section 4.3.2 for more information).
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4.3.1 – Connections for constant illumination measurements
Figure 12 shows the overview of the connections to the LED driver required to set
the light intensity to a constant, non modulated value.
Figure 12 – Overview of the connections for constant illumination experiments
The FRA V input must be shorted when not in use with the provided 50 Ohm
termination plug (see Figure 13).
Figure 13 – A 50 ohm terminator plug must be used to short the  FRA V input when this
input is not used
Make sure that the 50 Ohm plug is connected to the  FRA V input at all times!
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Note
If a FRA2 or FRA32M module is present, it is possible to replace the 50 Ohm
terminator plug by a BNC or SMB cable from the  V connector on the front
panel of the FRA module and the  FRA V input.
The light intensity of the LED array is controlled by setting the driving current
(passing through the LED power plug on the right-hand side). This driving current
is defined by setting the DAC164 #1 output to a value between 0 and 10 V.
This voltage value is converted by the LED driver to a constant current using the
following relationship:
𝑖𝑅𝑎𝑛𝑔𝑒
1000 𝑚𝐴
𝑖𝐿𝐸𝐷 = �
𝑉𝐷𝐴𝐶164 � = �
𝑉𝐷𝐴𝐶164 � = 100 𝑚𝐴/𝑉 ∙ 𝑉𝐷𝐴𝐶164
𝑉𝑅𝑎𝑛𝑔𝑒
10 𝑉
Where 𝑖𝐿𝐸𝐷 is the output driving current, in mA, 𝑖𝑅𝑎𝑛𝑔𝑒 is the current range of the
LED driver (1000 mA by default), 𝑉𝑅𝑎𝑛𝑔𝑒 is the input range of the LED driver (10 V)
and 𝑉𝐷𝐴𝐶164 is the output value of the DAC164 #1, in V.
Using the factory default values, setting the 𝑉𝐷𝐴𝐶164 to 1 V will result in a driving
current, 𝑖𝐿𝐸𝐷 of 100 mA. Setting the 𝑉𝐷𝐴𝐶164 to 0 V switches the light off and
setting the 𝑉𝐷𝐴𝐶164 to 10 V will generate the maximum light intensity.
Warning
Do not use DAC164 #2 to control the light intensity. The channel is internally
connected to the PGSTAT and is not suitable for this application.
Warning
Do not look directly into the light generated by the LED array.
4.3.2 – Connections for modulated illumination measurements
To modulate the light intensity, the  FRA V input is now connected to the front
panel output of the FRA module. The sinewave generated by the FRA module is
used to modulate the output of the LED Driver using a sinewave current
superimposed on the DC driving current.
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Note
The maximum modulation frequency is 20 kHz.
For the FRA2 module, the  V BNC plug can be connected to the  FRA V input
of the LED driver, as shown in Figure 14, using the provided SMB to BNC adaptor
plugs.
Figure 14 – Overview of the connections for modulated illumination experiments (FRA2)
The FRA32M module  V SMB plug can be connected to the  FRA V input of
the LED driver, as shown in Figure 15, using the provided SMB to BNC adaptor
plug.
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Autolab LED Driver User Manual
Figure 15 – Overview of the connections for modulated illumination experiments (FRA32M)
The light intensity of the LED array is controlled by setting the driving current
(passing through the LED power plug on the right-hand side). This driving current
is defined by setting the DAC164 #1 output to a value between 0 and 10 V and by
setting the amplitude of the FRA V output to a value between 0 and 0.35 V (RMS).
The difference between the DAC164 output and the FRA V output is converted by
the LED driver to a modulated current using the following relationship:
𝑖𝐿𝐸𝐷 = 𝑖𝐷𝐶 − 𝑖𝐴𝐶 = �
𝑖𝑅𝑎𝑛𝑔𝑒
(𝑉
− 𝑉𝐹𝑅𝐴 𝑉 )�
𝑉𝑅𝑎𝑛𝑔𝑒 𝐷𝐴𝐶164
𝑖𝐿𝐸𝐷 = 100 𝑚𝐴/𝑉 ∙ (𝑉𝐷𝐴𝐶164 − 𝑉𝐹𝑅𝐴 𝑉 )
Where 𝑖𝐿𝐸𝐷 is the output driving current, in mA, 𝑖𝑅𝑎𝑛𝑔𝑒 is the current range of the
LED driver (1000 mA by default), 𝑉𝑅𝑎𝑛𝑔𝑒 is the input range of the LED driver (10 V),
𝑉𝐷𝐴𝐶164 is the output value of the DAC164 #1, in V and 𝑉𝐹𝑅𝐴 𝑉 is the output value
of the FRA V, in V.
Warning
The 𝑉𝐷𝐴𝐶164 value must always be larger than 𝑉𝐹𝑅𝐴 𝑉 so that the 𝑉𝐷𝐴𝐶164 −
𝑉𝐹𝑅𝐴 𝑉 difference is always positive. When this difference is negative, the net
output driving current 𝑖𝐿𝐸𝐷 is 0 mA, regardless of the values of 𝑉𝐷𝐴𝐶164 and
𝑉𝐹𝑅𝐴 𝑉 .
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Note
The output driving current, 𝑖𝐿𝐸𝐷 is given by the difference between the constant
current, 𝑖𝐷𝐶 and the modulated current, 𝑖𝐴𝐶 .
Using the factory default values, setting the 𝑉𝐷𝐴𝐶164 to 1 V and the 𝑉𝐹𝑅𝐴 𝑉 to 0.1 V
will result in a DC driving current, 𝑖𝐷𝐶 of 100 mA, modulated by an AC current, 𝑖𝐴𝐶
of 10 mA. Setting the 𝑉𝐷𝐴𝐶164 − 𝑉𝐹𝑅𝐴 𝑉 to 0 V switches the light off and setting
the 𝑉𝐷𝐴𝐶164 − 𝑉𝐹𝑅𝐴 𝑉 to 10 V will generate the maximum light intensity.
Warning
Do not use DAC164 #2 to control the light intensity. The channel is internally
connected to the PGSTAT and is not suitable for this application.
Warning
Do not look directly into the light generated by the LED array.
4.3.3 – Optional connections
Additionally, a number of connections are available on the left and right hand side
of the driver. These connections are not mandatory, but can be used to facilitate
the measurement of experimental values used in IMPS and IMVS measurement.
Figure 16 shows the overview of the optional connections between the Autolab
and the LED driver. The connections shown in Figure 16 are complementary to the
connections shown in Figure 16 (shown in grey in Figure 16).
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Figure 16 – Overview of the optional (black) connections for modulated light intensity
experiments
The black connections shown in Figure 16 are optional and are provided for
convenience sake. These connections are required for signal readout during IMVS
and IMPS measurements. More information on these measurements can be found
in Section 8.4.
The FRA Y  output located on the right-hand side of the LED driver can be used
to feed the converted current to the  Y input of the FRA impedance analyzer.
The Eout and iout inputs, located on the left-hand side of the driver can be
connected to the corresponding outputs located on the monitor cable provided
with the Autolab PGSTAT (see Figure 17).
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Figure 17 – Monitor cable for the series 7 PGSTAT (above) and the series 8 PGSTAT (below)
Note
The PGSTAT101 and M101 module are not supplied with a monitor cable. This
cable must be ordered separately (article codes for PGSTAT101:
CABLE.MONITOR4, M101: CABLE.MONITOR.MAC). Please contact Metrohm
Autolab B.V. ([email protected]) or your local distributor for more
information.
The Eout and iout outputs signals are used for the IMVS and IMPS, respectively. By
feeding these two signals into the driver, the user can pass either one of these
signals to the FRA X output located on the right-hand side of the driver, using the
either one of the compatible DIO cables (see Figure 18).
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Figure 18 – Overview of the feedthrough connections for E out and iout
Two different DIO cables are compatible with the LED Driver:
•
For all the supported Autolab Potentiostat/Galvanostat instruments, except
the PGSTAT101 and the M101 module, a male DIN25 to female BNC cable
is supplied with the LED Driver kit (see Figure 19). This cable can be
connected to either P1 or P2 of the instrument. The female BNC connector
can be connected to the  DIO connector on the LED Driver using the
supplied 2 m long BNC cable.
Figure 19 - DIO cable for the Series 7 and Series 8 PGSTAT instruments
•
For the PGSTAT101 and the M101 module, a male DIN15 to female BNC
cable is available (see Figure 20). This cable can be connected to the DIO
port of the instrument or module. The female BNC connector can be
connected to the  DIO connector on the LED Driver using the supplied 2
m long BNC cable.
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Figure 20 - DIO cable for the Autolab PGSTAT101/M101
By setting the DIO input to high or low 4, the switch located in the driver can be
toggled remotely. The status LEDs located on the left-hand side of the driver will
indicate the selected input (see Figure 21).
Figure 21 – The iout/E out switch can be set remotely through the DIO input (top, DIO status UP
or disconnected – iout selected, bottom, DIO status DOWN – E out selected)
Please refer to the External devices tutorial, available from the Help menu in NOVA for more
information on the control of the DIO port(s) of the Autolab.
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By default, when no connection to the DIO is present, the iout is always selected,
indicated by the status LED on the left-hand side. The switch can also be toggled
through an analog voltage. Supplying more than 2.5 V on this DIO input triggers
the switch.
Note
Using the built in Eout/iout switch is not mandatory for IMVS/IMPS measurements,
but is recommended because it facilitates the wiring schemes.
4.4 – Autolab connections to analog outputs
The Autolab LED Driver provides two analog outputs, labelled DYN V  and FRA
Y , respectively, on the right-hand side of the driver. These two outputs can be
connected to the external inputs of the Autolab.
Depending on the output, the following values are provided:
•
•
DYN V : this output provides the potential difference between the
 DAC 1 input and the  FRA V input of the LED Driver, in volts. The
output range is between 0 V and 10 V.
FRA Y : this output provides the value of the driving current passing
through the LEDs, converted to voltage by a current-to-voltage converter.
The current follower used in this circuit has a single current range of 1 A,
with a 1 V/A conversion. The output range is between 0 V and 1 V.
Figure 22 shows the values recorded on the DYN V  plug in function of the
specified driving current. A linear relationship is observed between the two values,
and the measured slope corresponds to 0.01 V/mA.
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Figure 22 – Output value of the DYN V plug plotted against the specified driving current
Figure 23 shows the values recorded on the FRA Y  plug in function of the
specified driving current. A linear relationship is observed between the two values,
and the measured slope corresponds to 0.001 V/mA.
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Figure 23 – Output value of the FRA Y  plug plotted against the specified driving current
5 – Software control
The Autolab LED driver is intended to be controlled by the NOVA software. The
control of the driver is performed through the use of analog and/or digital
settings:
•
•
Analog control of the light intensity and modulation, if applicable.
Digital control of the Eout/iout through the DIO port.
This section provides details on the light intensity control.
5.1 – Analog control of the light intensity
Regardless of the type of experiment, the light intensity of the LED is controlled by
supplying a voltage value between 0 V and 10 V to the DAC 1 input and the FRA
V input of the driver. At all times, the value supplied to the FRA V input must be
smaller than the value supplied to the DAC 1 input. The supplied voltage
difference between the inputs is converted into a driving current,
𝑖𝐿𝐸𝐷 given by:
𝑖𝐿𝐸𝐷 = 𝑖𝐷𝐶 − 𝑖𝐴𝐶 = �
𝑖𝑅𝑎𝑛𝑔𝑒
(𝑉
− 𝑉𝐹𝑅𝐴 𝑉 )�
𝑉𝑅𝑎𝑛𝑔𝑒 𝐷𝐴𝐶164
𝑖𝐿𝐸𝐷 = 100 𝑚𝐴/𝑉 ∙ (𝑉𝐷𝐴𝐶164 − 𝑉𝐹𝑅𝐴 𝑉 )
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Or, when no voltage is supplied on the FRA V input (50 Ohm termination plug in
place) by:
𝑖𝑅𝑎𝑛𝑔𝑒
𝑖𝐿𝐸𝐷 = �
𝑉
�
𝑉𝑅𝑎𝑛𝑔𝑒 𝐷𝐴𝐶164
𝑖𝐿𝐸𝐷 = 100 𝑚𝐴/𝑉 ∙ 𝑉𝐷𝐴𝐶164
Where 𝑖𝐿𝐸𝐷 is the output driving current, in mA, 𝑖𝑅𝑎𝑛𝑔𝑒 is the current range of the
LED driver (1000 mA by default), 𝑉𝑅𝑎𝑛𝑔𝑒 is the input range of the LED driver (10 V),
𝑉𝐷𝐴𝐶164 is the output value of the DAC164 #1, in V and 𝑉𝐹𝑅𝐴 𝑉 is the output value
of the FRA V, in V.
Using the factory default values, setting the 𝑉𝐷𝐴𝐶164 to 1 V and the 𝑉𝐹𝑅𝐴 𝑉 to 0.1 V
will result in a DC driving current, 𝑖𝐷𝐶 of 100 mA, modulated by an AC current, 𝑖𝐴𝐶
of 10 mA. Setting the 𝑉𝐷𝐴𝐶164 − 𝑉𝐹𝑅𝐴 𝑉 to 0 V switches the light off and setting
the 𝑉𝐷𝐴𝐶164 − 𝑉𝐹𝑅𝐴 𝑉 to 10 V will generate the maximum light intensity.
Note
When the input voltage is 90 mV or less, the current output will be switched off
and the output current will be 0 mA. The minimum current is therefore limited
to 9 mA.
5.1.1 – Settings for the DAC 1 input
The DAC 1 input of the LED driver controls the DC light intensity. This setting is
defined in the software through the Control external device (DAC) command,
available from the Measurement – general group of commands (see Figure 24).
Note
The Control external device (DAC) command is an Advanced command. Adjust
the Profile in NOVA if necessary.
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Figure 24 – The Control external device (DAC) command is used to set the DC light intensity
The Control external device (DAC) command is a Timed command, and as such
must always be included in a Timed procedure. This command has the following
parameters:
Parameter
Set value
Description
The converted value required to control the external
device (the value corresponds to (offset + DAC voltage *
slope)
DAC channel
The DAC channel used to control the external device
(DAC 3, corresponding to DAC 1 on the front panel,
should always be used)
Conversion offset
Defines the offset for the value conversion
Conversion slope
Defines the slope for the value conversion
For Autolab LED driver, the conversion offset should be set to 0 and the
conversion slope should be set to (10 V/1000 mA) if the value should be defined in
mA or to (10 V/1 A) if the value should be defined in A (see Figure 25).
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Figure 25 – The settings required for the Control external device (DAC) command (Top:
defined in mA, Bottom: defined in A)
For bookkeeping purposes, it is convenient to rename the command and to
indicate which units are used to set the light intensity. In the rest of this
document, the V to mA conversion will be assumed (see Figure 26).
Figure 26 – Renaming the command (note the units)
Furthermore, it is recommended to save the modified command in the My
commands database, by right-clicking the command and choosing the Save in My
commands option (see Figure 27).
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Figure 27 – Saving the command in the My commands database
The command will appear in the My commands group of commands. It can be
used at any time in the procedure (see Figure 28).
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Figure 28 – The saved command is available in the My commands group
5.1.2 – Settings for the FRA V input
The FRA V input of the LED driver controls the AC light intensity modulation. This
setting is defined in the software through the FRA measurement external
command, available from the Measurement – impedance group of commands (see
Figure 29).
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Figure 29 – The FRA measurement external command is used to modulate the light intensity
Note
When no modulation is required in the experiment, the FRA V input of the LED
driver must be shunted using a 50 Ohm terminator plug (included, see
page 18).
The FRA measurement external command is used to perform a FRA measurement
using the external inputs and outputs of the FRA module. The output of the FRA
module is used to generate a sinewave which is fed into the LED Drive FRA V
input. This sinewave, supplied as a voltage (0 – 5 V top amplitude range) is
converted into an AC driving current.
The FRA measurement external command is a composite command (see Figure
30).
Note
The FRA measurement external command is an Advanced command. Adjust the
Profile in NOVA if necessary.
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Figure 30 – The commands and parameters of the FRA measurement external command
The settings for controlling the light source modulation are defined in the FRA
sampler. To edit these settings, click the
button located next to the FRA
sampler in the FRA single frequency command (see Figure 31).
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Figure 31 – The settings required for light source modulation are defined in the FRA sampler
The FRA sampler window will be displayed (see Figure 32).
Figure 32 – The FRA sampler window
The FRA sampler window is used to define the settings for the generation of the
sinewave and the analysis of the transfer function. To control the modulation of
the LED directly in AC driving current, the Input amplitude multiplier must be
specified properly.
Click the
checkbox in the top left corner and specify the conversion factor
required to convert the supplied voltage into driving current (10 V/1000 mA). In
the units field indicate the units used for this converted AC signal (see Figure 33).
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Figure 33 – The settings required for the input amplitude
Note
In the example shown in Figure 34, the conversion settings are defined in such
way that the amplitude can be defined as AC driving current in mA. If the AC
unit is to be defined in A, the conversion factor needs to be adjusted (to 10, see
page 30 for more information).
The settings for the transfer function, defined in the Channel X and Channel Y
sections of the FRA Sampler depend on the type of measurement. More
information is provided in Sections 8.4.1.1 and 8.4.2.1.
Press the
button to close the FRA sampler.
The applied light modulation can now be specified in the FRA frequency scan
command. Click the
button located next to the FRA frequency scan command
to open the FRA frequency scan editor window (see Figure 34).
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Figure 34 – Opening the frequency editor
The FRA frequency scan editor window will be displayed (see Figure 35).
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Figure 35 – The FRA frequency scan editor window
The units of the amplitude are indicated in the FRA frequency editor window. In
this example, the conversion factor defined in Figure 33 specified that the units of
the amplitude are mA.
The maximum amplitude, 𝑖𝐴𝐶 (𝑀𝐴𝑋), that can be specified is 350 mA (RMS) or 500
mA (TOP). However, for the default LED covers supplied by Metrohm Autolab, the
total driving current cannot exceed the maximum limit of 700 mA. The applied
amplitude must also be larger than the DC driving current, at all time.
0 𝑚𝐴 ≤ 𝑖𝑡𝑜𝑡𝑎𝑙 = 𝑖𝐷𝐶 + 𝑖𝐴𝐶 (𝑇𝑂𝑃) ≤ 700 𝑚𝐴
5.1.3 – Settings for the DIO control
The  DIO BNC connector can be used to switch remotely between the  E out
or i out inputs on the LED Driver, using the DIO port(s) provided by the Autolab,
as explained in Section 4.3.3.
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To control the DIO of the Autolab, the Autolab control command 5 must be used
to initialize the DIO port used in the experiment (not required for the PGSTAT101
and the M101 module). The DIO port used must be initialized at the beginning of
the procedure.
Note
Pin #1, located on DIO port A is used to control the switch.
To initialize the DIO port A, located on either P1 or P2, the direction setting for
this port must be set to Output, using the drop-down list provided in the Autolab
control window (see Figure 36).
Figure 36 – Setting the direction of Port A of connector P1 to Output
More information on the settings of the DIO ports can be found in the External devices tutorial.
More information on the Autolab control command can be found in the Autolab control turorial.
Both tutorials can be found in the Help menu of NOVA.
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After the port is initialized, the status of Pin #1 can be set at any time to high (5 V)
or low (0 V), using the Autolab control command.
•
•
Low (00000000 – 0): when pin #1 is set to low status (0 V), the  E out
input is active. This is also the default status when nothing is connected to
the  DIO input of the LED Driver.
High (00000001 – 1): when pin #1 is set to high (5 V), the  i out input
is active. The switch will be kept in this position as long as pin #1 is set to
high.
The status of pin #1 of the initialized port can be changed at any time using the
Autolab control window. The status can be set as a decimal value (0 or 1), or as a
binary string (00000000 or 00000001). The status defined is permanent until
changed (see Figure 37).
Figure 37 – Setting the status of pin #1
For the PGSTAT101 or M101 module, the same settings are used. However, in this
case, only a single port is available (see Figure 38). Port A of the DIO connector of
the PGSTAT101 or M101 does not have to be initialized since it is hardwired to
output.
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Figure 38 – Setting the status of pin #1 for the PGSTAT101 or M101 module
6 – Light source calibration
Quantitative results can only be obtained after the calibration of the light source.
This can be done by using a calibrated photodiode exposed to the light source at a
controlled distance on the optical bench. The calibration can be performed with
the Autolab or with external digital multimeters. In this manual, the procedure
used in combination with the Autolab is described.
The LED Driver kit is supplied with a calibrated photodiode, embedded into a
cylindrical holder (see Figure 39). The measurement range of the photodiode is
from 350 nm to 1100 nm.
Figure 39 – The photodiode holder (front view)
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The photodiode holder is fitted with three female 4 mm banana connectors,
labeled WE (red), CE (black) and GND (green), respectively. These connectors are
used to accommodate the cell connectors provided by the Autolab PGSTAT (see
Figure 40).
Figure 40 – The photodiode holder (back view)
The photodiode holder is also supplied with an additional plastic cover which can
be mounted on top of the calibrated photodiode. This cover is designed to hold a
filter 6 to protect the photodiode from exposure to light intensities beyond the
damage threshold.
Warning
The photodiode will be irreversibly damaged when exposed to a light intensity
of 100 mW/cm2 or more. For very high intensity measurements, a neutral
density filter may be required. Please contact your Metrohm Autolab distributor
for more information.
The calibration procedure requires the calibrated photodiode to be placed at the
required distance from the light source and to expose the photodiode to different
light intensities (controlled by the driving current supplied by the LED Driver). The
photodiode current can be converted to light intensity using the conversion values
reported in the calibration certificate of the calibrated photodiode supplied with
the LED Driver kit (see Figure 41).
To protect the photodiode a reflective neutral density filter can be used. The size of the filter is
1.27 cm (1/2 inch).
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Figure 41 – Calibration data provided on the calibration certificate
The calibration certificate provides a table of wavelengths (λ, in nm) and
responsivity (η, in A/W). The responsivity values are reported in absolute values
and should be normalized with respect to the active surface area of the
photodiode (13 mm²).
Using this strategy, it is relatively easy to establish a driving current-to-light
intensity correlation, as shown in Figure 42. The data shown in this plot was
obtained at a distance of 20 cm, using a 590 nm LED cover (Amber).
𝜑
The light intensity, 𝑃𝐿𝐸𝐷 , is calculated from the measured photodiode current, 𝑖𝑆𝐶 ,
divided by the surface of the photodiode (0.13 cm²) and divided by the
responsivity reported in the calibration certificate (see Figure 41).
𝑃𝐿𝐸𝐷
𝜑
𝜑
𝑖
𝑖𝑆𝐶
= � 𝑆𝐶 � = �
�
𝐴∙𝜂
0.13 𝑐𝑚² ∙ 0.279 𝐴/𝑊
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Figure 42 – Driving current to light intensity conversion curve, measured at 590 nm (Amber)
To use the photodiode, connect the RE/CE leads from the PGSTAT to the CE plug
on the photodiode holder and connect the WE/S to the WE plug on the
photodiode holder. Connect the green ground plug embedded in the cell cables of
the Autolab to the matching GND banana connector of the photodiode holder.
Note
The photodiode current must be measured at short-circuit conditions (0 V
applied) and at known wavelength.
7 – Cell holder
The calibrated photodiode holder is fitted with two sliding clamps that can be
used to fix the cell onto the holder, provided that the cell is small enough to fit in
this space. This holder is designed for a common form factor for experimental
solar cells, like the one shown in Figure 42.
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Figure 43 – Typical experimental cell design suitable for the Autolab LED Driver kit
The clamps can be repositioned if necessary by loosening the two screws that hold
them in place (see Figure 44).
Note
If the cell does not fit between the two clamps, an external holder can be used
to place the cell close to the photodiode. Metrohm Autolab cannot anticipate
all the possible cell configurations and it is left to the user to find a suitable
solution, if necessary.
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Figure 44 – The cell can be mounted onto the photodiode holder
8 – Experiment description
This section provides a description of different experiments that can be carried out
with the LED Driver kit, using the information provided in the previous sections.
8.1 – Cell connections
Photovoltaic devices are usually characterized in the so-called two electrode mode.
In this mode, the Autolab PGSTAT is connected to both the anode and the
cathode using the CE/RE and WE/S, respectively (see Figure 45).
Figure 45 – Overview of the connections to the cell
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In this configuration, the potential difference across the cell is measured between
the RE and the S, using the differential amplifier electrometer of the Autolab
PGSTAT. The current is measured between the CE and the WE.
Note
By convention, the potential of the cell under operating conditions is always
positive and the current, under operating conditions is always negative.
8.2 – DC measurements at constant illumination
DC measurements at constant illumination are the simplest measurements possible
with the PGSTAT in combination with the LED Driver. During these experiments,
the light source is set to a user defined driving current to provide constant
illumination on the cell, while the PGSTAT measures the i/V curve of the cell. The
i/V curve can be recorded either potentiostatically or galvanostatically.
Note
The Power cannot be measured directly. It can be calculated by multiplying the
potential, V, by the current, i.
The following DC measurements are possible:
•
•
Measurement of the i/V curve of the cell
Charge extraction measurements
8.2.1 – i/V and power curves at constant illumination
Characterization of solar cells usually requires the determination of i/V curves. As
the potential of the cell is scanned from 0 V (short circuit conditions) to the open
circuit potential, the current changes from the maximum value (short-circuit
current, 𝑖𝑆𝐶 ) to OCP (0 A). A typical example is shown in Figure 46.
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Figure 46 – i/V curve (blue) and power curve (red) obtained with the PGSTAT in combination
with a 590 nm LED. The light intensity is 1.655 mW/cm2, the cell is a Dye Sensitized Solar Cell
The i/V curves and power curves can be recorded at different light intensities, by
varying the driving current. If the conversion of driving current to light intensity in
W/cm² is known, then the light intensity to which the cell is exposed can be
controlled directly (see Section 6).
From the short circuit current (𝑖𝑆𝐶 ), open circuit potential (𝑉𝑂𝐶𝑃 ) and the maximum
power point (𝑃𝑀𝐴𝑋 ), the fill factor (𝐹𝐹) of the cell can be calculated.
𝐹𝐹(%) = �
𝑖𝑀𝐴𝑋 ∙ 𝑉𝑀𝐴𝑋
𝑃𝑀𝐴𝑋
� ∙ 100 = �
� ∙ 100
𝑖𝑆𝐶 ∙ 𝑉𝑂𝐶𝑃
𝑖𝑆𝐶 ∙ 𝑉𝑂𝐶𝑃
𝐹𝐹(%) = �
82.558 𝜇𝑊
� ∙ 100 = 61.04 %
186.58 𝜇𝐴 ∙ 0.656 𝑉
From the light intensity (𝑃𝐼𝑁 ), the wavelength (𝜆) and the short-circuit current
density (𝑗𝑆𝐶 ) the incident photon-to-current conversion efficiency (ICPE) can be
calculated.
𝑗𝑆𝐶
𝐼𝑃𝐶𝐸 = 1239 �
� ∙ 100
𝑃𝐼𝑁 ∙ 𝜆
0.325 𝑚𝐴/𝑐𝑚2
𝐼𝑃𝐶𝐸 = 1239 �
� ∙ 100 = 41.2 %
𝑚𝑊
1.655
∙
590
𝑛𝑚
𝑐𝑚2
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8.2.1.1 – Software implementation
DC measurements with the PGSTAT in combination with the LED Driver can be
performed using a NOVA procedure. The light intensity can be controlled using
the Control external device (DAC) command, as explained in Section 5.1.1.
This command can be combined in a measurement with a LSV staircase or LSV
staircase galvanostatic command, depending on the experimental conditions.
Under potentiostatic condition, it is common practice to start the scan a 0 V
(short-circuit conditions) and stop the scan when the current becomes zero
(open circuit conditions). An example of a procedure for this type of measurement
is shown in Figure 47.
Figure 47 – An example of a procedure used to measure the i/V curve of a cell
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Note
A cutoff condition can be used to detect the potential at which the current
changes polarity (see Figure 47).
Figure 48 – A cutoff condition can be used to detect the point where the current changes
polarity
8.2.1.2 – Possible refinements
The sequence shown in Figure 47 is a very simple sequence which offers limited
possibilities. It is possible to combine this sequence with other NOVA commands
in order to build a complete measurement sequence. Since the description of such
a sequence is left to the requirements of the users, it falls outside of the scope of
this document. A few tips are provided below:
•
A Repeat for each value command, with the set current values defined in
the values sequence of the repeat command can be used in combination
with the Control external device (DAC) command (renamed to Control LED
Driver (mA)). This will repeat the whole measurement sequence for each
pre-defined value (see Figure 49).
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•
The Calculate signal command can be added to the sequence in order to
automatically calculate the Power signal, using the values of the potential
and the current.
Figure 49 – Using the Repeat for each value command in combination with the Control
external device (DAC) command
8.3 – AC measurements at constant illumination
The LED Driver can be used in combination with the PGSTAT/FRA to obtain the
electrochemical impedance spectrum of the device under test (DUT) under
constant illumination. Electrochemical impedance measurements can be
performed while illuminating the cell, potentiostatically or galvanostatically.
Typically, these measurements are performed at open circuit or at short-circuit.
The measurement strategy is the same as for a DC measurement at constant
illumination. The light intensity is set to a fixed value using the Control external
device (DAC) command.
Warning
When performing AC measurements at constant illumination, the

of the LED Driver must be shorted using the supplied 50 Ohm terminator plug
as explained in Section 4.3.1.
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8.3.1 – EIS measurements at constant illumination
The standard Autolab procedure FRA impedance potentiostatic and FRA
impedance galvanostatic procedures can be used to perform EIS measurements at
constant illumination. The Control external device (DAC) command can be added
to the preconditioning stage in either one of the procedures. Figure 50 shows a
possible procedure that can be used to perform EIS measurements on the DUT.
Figure 50 – The FRA impedance potentiostatic procedure modified using the Control external
device (DAC) command
Note
The Control external device (DAC) command is renamed to Control LED Driver
(mA) in this example (see Section 5.1.1).
Typical electrochemical impedance spectroscopy measured at different light
intensities are illustrated in Figure 51. As the illumination level increases, the
Nyquist plot indicates a lower total resistance.
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The data shown in Figure 51 has been recorded at 590 nm, at open circuit
potential, using an amplitude of 25 mV.
Figure 51 – Typical Nyquist plots recorded at different light intensities
8.4 – AC measurements at modulated illumination
While it is possible to modulate the current or the potential in a classic
electrochemical impedance spectroscopy measurement, as explained in Section
8.3.1, it is also possible to modulate the light intensity directly. Two measurement
possibilities exist:
•
•
Intensity-modulated photovoltage spectroscopy (IMVS)
Intensity-modulated photocurrent spectroscopy (IMPS)
8.4.1 – Intensity modulated photovoltage spectroscopy (IMVS)
The LED Driver can be used in combination with the PGSTAT/FRA interface to
record intensity modulated photovoltage spectroscopy measurements on the
device under test (DUT).
During an intensity modulated photovoltage spectroscopy (IMVS) measurement,
the DUT is exposed to a constant light intensity, 𝜑0 , modulated by a small
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amplitude AC perturbation, Δ𝜑. The DUT settles at a constant voltage, 𝑉0,
modulated by a small amplitude AC response, Δ𝑉.
The IMVS impedance is the transfer function, H, between the AC voltage (Δ𝑉) and
the AC light modulation (Δ𝜑).
Figure 52 shows a schematic overview of the experimental setup.
Figure 52 – Overview of the IMVS measurement setup
The fixed light intensity, 𝜑0 is provided by the DAC voltage using the Control
external device (DAC) command, as described in the Sections 4.3.1 and 5.1.1. The
AC modulation, Δ𝜑, is provided by the FRA  V connector, using the FRA
measurement external command, as described in Section 4.3.2 and 5.1.2.
The transfer function, 𝐻(𝜔), is monitored using the external inputs of the FRA
module:
•
•
The Eout signal from the PGSTAT is fed into the FRA  X input connector of
the FRA module.
The FRA Y  output of the LED Driver is fed into the FRA  Y input
connector of the FRA module.
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8.4.1.1 – IMVS measurements
IMVS measurements are usually carried out at open circuit potential (OCP).
Figure 53 shows an example of an IMVS procedure. In the first step of the
procedure, the light intensity is set to a fixed DC level using the Control external
device (DAC) command. The cell is then set open circuit conditions by applying 0 A
in Galvanostatic mode.
Figure 53 – An example of IMVS procedure
The second stage of the procedure performs the IMVS measurement using the
FRA measurement external command (see Figure 54).
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Figure 54 – The FRA measurement external command is used during the IMVS frequency scan
Before the measurement can be performed properly, the parameters for the
transfer function must be set in the FRA Sampler. Click the
button located next
to the FRA sampler parameter of the FRA signal frequency command (see Figure
54).
The parameters for the transfer function are defined in the Channel X and Channel
Y of the FRA sampler window (see Figure 55).
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Figure 55 – The transfer function parameters are specified in the FRA sampler
(Channel X and Channel Y)
Note
Pin #1, located on DIO port A is used to control the switch. In Figure 54, the
parameters for the Input amplitude have already been set according to the
instructions indicated in Section 5.1.2.
For IMVS measurements, the following settings are required (see Figure 56):
•
•
Channel X: this input is used to measure the AC cell potential during the
frequency scan. This input corresponds to the Eout coming from the
Autolab, which corresponds to the inverted cell potential (-EDUT). This input
is therefore specified in V and requires a multiplier of (-1).
Channel Y: this input is used to the measure the AC LED Driver current
during the frequency scan. The FRA Y  output of the LED Driver is
connected to this input. The values from this connection are expressed in V
(corresponding to the converted current). The conversion factor is 1 V/A.
This signal is therefore specified in A and requires a multiplier of 1.
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Figure 56 – Setting the parameters for the FRA sampler
Note
Using the FRA sampler window, it is possible to specify if the time domain
information, corresponding to the raw sinewaves recorded by the FRA module,
have to be sampled during the measurement1. It is recommended to check both
checkboxes for IMVS measurements, in order to verify the quality of the data
during the experiments (see Figure 56).
Figure 57 – Sampling the time domain data for Channel X and Channel Y
Close the FRA sampler with the
button.
The frequency scan can now be defined in the procedure editor by clicking the
button next to the FRA frequency scan command (see Figure 58).
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Figure 58 – Opening the FRA frequency scan editor
The FRA frequency scan window will be displayed. The highest frequency, lowest
frequency, number of frequencies and frequency distribution can be defined in this
editor (see Figure 59). The amplitude can also be defined in mA (or in A,
depending on the settings used in the FRA sampler).
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Figure 59 – The FRA frequency scan editor window
Once the frequency range is defined, the measurement can be performed. Figure
60 shows a typical IMVS measurement on a DSC. The measurement is performed
at 590 nm, at a constant light intensity of 1.7 mW/cm2. The AC amplitude is 10 %
of the DC light intensity.
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Figure 60 – A typical IMVS measurement on a dye-sensitized solar cell
8.4.2 – Intensity modulated photocurrent spectroscopy (IMPS)
The LED Driver can be used in combination with the PGSTAT/FRA to record
intensity modulated photocurrent spectroscopy measurements on the device
under test (DUT).
During an intensity modulated current spectroscopy (IMPS) measurement, the DUT
is exposed to a constant light intensity, 𝜑0 , modulated by a small amplitude AC
perturbation, Δ𝜑. The DUT settles at a constant current, 𝑖0 , modulated by a small
amplitude AC response, Δ𝑖.
The IMPS impedance is the transfer function, H, between the AC current (Δ𝑖) and
the AC light modulation (Δ𝜑).
Figure 61 shows a schematic overview of the experimental setup.
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Figure 61 – Overview of the IMPS measurement setup
The fixed light intensity, 𝜑0 is provided by the DAC voltage using the Control
external device (DAC) command, as described in the Sections 4.3.1 and 5.1.1. The
AC modulation, Δ𝜑, is provided by the FRA  V connector, using the FRA
measurement external command, as described in Sections 4.3.2 and 5.1.2.
The transfer function, 𝐻(𝜔), is monitored using the external inputs of the FRA
module:
•
•
The iout signal from the PGSTAT is fed into the FRA  X input connector of
the FRA module.
The FRA Y  output of the LED Driver is fed into the FRA  Y input
connector of the FRA module.
Warning
The automatic current ranging option cannot be used in an IMPS
measurement.
8.4.2.1 – IMPS measurements
IMPS measurements are usually carried out at short-circuit conditions.
Figure 62 shows an example of an IMPS procedure. In the first step of the
procedure, the light intensity is set to a fixed DC level using the Control external
device (DAC) command. The potential is set to 0 V (short-circuit conditions).
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Figure 62 – An example of IMPS procedure
The second stage of the procedure performs the IMPS measurement using the FRA
measurement external command (see Figure 63).
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Figure 63 – The FRA measurement external command is used during the IMPS frequency scan
Before the measurement can be performed properly, the parameters for the
transfer function must be set in the FRA Sampler. Click the
button located next
to the FRA sampler parameter of the FRA signal frequency command (see Figure
63).
The parameters for the transfer function are defined in the Channel X and Channel
Y of the FRA sampler window (see Figure 64).
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Figure 64 – The transfer function parameters are specified in the FRA sampler
(Channel X and Channel Y)
Note
In Figure 63, the parameters for the Input amplitude have already been set
according to the instructions indicated in Section 5.1.2.
For IMPS measurements, the following settings are required (see Figure 65):
•
7
Channel X: this input is used to measure the AC cell current during the
frequency scan. This input corresponds to the iout coming from the Autolab,
which corresponds to the converted cell current (which depends on the
selected current range 7). This input is therefore specified in A and requires
a multiplier that depends on the current range used in the measurement.
The iout of the Autolab is given by the measured current (in A) divided by
the current range (in A/V). Table 2 shows the multiplier values depending
on the selected current range. Figure 65 shows the settings for a
measurement in the 1 mA current range.
Please refer to the NOVA Getting Started manual for more information.
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Current range
1A
Conversion factor
1 A/V
Multiplier
1
100 mA
100 mA/V
0.1
10 mA
10 mA/V
0.01
1 mA
1 mA/V
0.001
100 µA
100 µA/V
0.0001
10 µA
10 µA/V
0.00001
1 µA
1 µA/V
0.000001
100 nA
100 nA/V
0.0000001
10 nA
10 nA/V
0.00000001
Table 2 – Multiplier factors per current range
•
Channel Y: this input is used to the measure the AC LED Driver current
during the frequency scan. The FRA Y  output of the LED Driver is
connected to this input. The values from this connection are expressed in V
(corresponding to the converted current). The conversion factor is 1 V/A.
This signal is therefore specified in A and requires a multiplier of 1.
Figure 65 – Setting the parameters for the FRA sampler
Note
Using the FRA sampler window, it is possible to specify if the time domain
information, corresponding to the raw sinewaves recorded by the FRA module,
have to be sampled during the measurement1. It is recommended to check both
checkboxes for IMPS measurements, in order to verify the quality of the data
during the experiments (see Figure 65).
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Figure 66 – Sampling the time domain data for Channel X and Channel Y
Close the FRA sampler with the
button.
The frequency scan can now be defined in the procedure editor by clicking the
button next to the FRA frequency scan command (see Figure 67).
Figure 67 – Opening the FRA frequency scan editor
The FRA frequency scan window will be displayed. The highest frequency, lowest
frequency, number of frequencies and frequency distribution can be defined in this
editor (see Figure 68). The amplitude can also be defined in mA (or in A,
depending on the settings used in the FRA sampler).
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Figure 68 – The FRA frequency scan editor window
Once the frequency range is defined, the measurement can be performed. Figure
69 shows a typical IMPS measurement on a DSC. The measurement is performed
at 590 nm, at a constant light intensity of 1.7 mW/cm2. The AC amplitude is 10 %
of the DC light intensity.
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Figure 69 – A typical IMPS measurement on a DSC
8.5 – Safety settings when measurement is aborted
When measurements are manually interrupted, by clicking the Stop button, or
when a cutoff condition is met that stops the complete procedure, it may be
necessary to completely switch off the light source and the cell.
To define the end conditions for the Autolab LED Driver kit and the cell, the End
status Autolab settings can be defined in the procedure editor.
The End status Autolab can be defined by clicking the
parameter in the procedure editor (see Figure 70).
button next to this
Figure 70 – Editing the End status Autolab
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The Autolab control editor will be displayed (see Figure 71). Using the drop-down
boxes, the required adjustments can be defined.
Figure 71 – The End status Autolab is defined using the Autolab control window
The following settings can be relevant for this application:
•
Cell off: to switch the cell off, set the Cell drop-down list on the WE(1) tab
of the Autolab control window to Off (see Figure 72).
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Figure 72 – Switching the cell off
•
Light off: to switch the light source off, set the DAC voltage property to 0
V on the DAC(1) tab (see Figure 73).
Figure 73 – Setting the DAC voltage to 0 V
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•
Modulation off: to switch off the modulation generated by the FRA
module, if applicable, set the DSG property to off using the provided dropdown list on the FRA(1) tab (see Figure 74).
Figure 74 – Switching the output of the FRA module off
9 – Thermal considerations
Although the LED holder has been designed for optimal temperature
management, the behaviour of the LEDs located onto the PCB is affected by
temperature variations. Since the overall temperature of the LED PCB increases as
the driving current increases, the light output can be affected, leading to a nonlinear relationship between driving current and light intensity.
Figure 75 and Figure 76 show how the relative light output of the LEDs is affected
by the temperature. The light intensity is normalized with respect to the light
intensity measured at 25 °C.
Warning
The LED light source can get hot when operated at high driving currents.
Always allow the light source to cool down before touching it.
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Figure 75 – Relative light output vs thermal pad temperature for green, cyan, blue
and royal-blue 8
Figure 76 – Relative light output vs thermal pad temperature for red, red-orange
and amber 9
8
Adapted from LUXEON Rebel, Direct Color Portfolio, High power, colored LEDs, Technical
Datasheet DS65.
9
Adapted from LUXEON Rebel, Direct Color Portfolio, High power, colored LEDs, Technical
Datasheet DS65.
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Appendix 1 – Modification of the input range of the FRA2
module
By default, the external inputs of the FRA2 modules shipped before July 2009
(revision number 8.0 and lower) can be used to record analog signals in the ± 5 V
range. For this application, analog signals in the ± 10 V range are required. In
order to be able to record voltages between 5 and 10 V, the FRA2 modules with
revision numbers lower than 8.1 need to have the extended range offset DACs
activated.
This requires a simple hardware modification. Only qualified personnel can
perform this modification. Please contact Metrohm Autolab B.V. ([email protected]) or your local distributor for more information.
Note
This modification is not applicable for the µAutolabIII/FRA2.
The FRA2 input range is directly specified in the Hardware setup. Start NOVA and
open the Hardware setup (Tools – Hardware setup). Locate the FRA2 offset DAC
range toggle at the bottom of the Hardware setup window (see Figure 77).
Figure 77 – The 10 V input range can be specified in the Hardware setup directly
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Set this toggle to 10 V as shown in Figure 77. Click OK to close the Hardware
setup and save the modifications when prompted.
This modification is permanent.
If necessary, new labels (article codes: CAB.LABEL.FRA2..V10.V and
CAB.LABEL.FRA2.V10.XY) can be ordered for the modified FRA2 module (see
Figure 78).
Figure 78 – FRA2 10 V input range labels
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Appendix 2 – Calibrated Photodiode
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Appendix 3 – Hardware specifications
The specifications of the Autolab LED Driver kit are listed in Table 3.
Power supply
Maximum current
Maximum LED current
Input voltage range
Output voltage range
Maximum modulation amplitude
Maximum modulation frequency
Operating temperature
18 V, 1.2 A
1000 mA
700 mA
90 mV – 10 V
0 mV – 1000 mV
5 V (TOP)
20 kHz
0 – 40 °C
Table 3 – Specifications of the Autolab LED Driver
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07/2012
Kanaalweg 29/G
3526 KM Utrecht
The Netherlands
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