Version 1.1, Please cite (A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices, Seger, B., Hansen, O., Vesborg, P.C.K., Solar RRL, DOI:10.1002/solr.201600013) when using this mode. The program was optimized for Firefox, but should work on all major browsers. Brian Seger was the sole programmer of this model, thus pleas contact him for any questions or
issues relating to the model here . Read more about the web-based model here.
General
Conditions
(Always uses an AM1.5 spectrum)
Reactor temperature :
K
It
is recommended that the water depth value is maintained since
the matching photoabsorber (to your photoelectrode) probably
still needs to account for water absorption
How much water the light
needs to penetrate through before it reaches the photoabsorber(s):
(For tandem devices: Only bottom cell is affected by water absorption (?): )
Only click this for tandem devices where the irradiation side of the top cell photoabsorber never sees electrolyte. If this option is used it will assume the electrolyte
will be between the top cell photoabsorber and bottom cell photoabsorbers. This approach is not common. If this option is used for single photoabsorbers, it will equivalent to setting the water depth = 0 cm.
This is the light concentraion of the AM1.5 spectra.
For light concentrations above 1.00, AM1.5 (Direct + Circumsolar) is used since this spectrum is meant for concentrator cells.
For no light concentration (i.e. Concentration = 1) AM1.5 Global is used.
For light concentration between 0 and 1, the program uses a given fraction of the AM1.5 Global spectra.
The precision to which the program calculates current is automatically adjusted to account for concentration. One can readjust this if desired by clicking on the 'Precision and Ploting' option.
Concentration: times
AM1.5
Optimize by allowing for additional bias to be used (?):
This adds additional bias to the device which helps the photovoltage overcome the thermodynamics and losses of the system.
This additional energy used in creating the bias is subtracted off when the efficiency is calculated.
Please realize bias here relates to a 2-electrode device, and should not be confused with bias from a 3-electrode device.
This will normally be zero unless you have a wired device or have unconductive protection layers
Photoabsorber Options
Click to modify light absorption parameters
Photon matching (via thinning top cell) (?):
Checking this box will thin
the thickness (and current) of the top cell photoabsorber to
match that of the bottom cell photoabsorber (when applicable)
Top cell for tandem device (or data for single photoabsorber)
Parasitic light loss (catalyst or proteciton layer absorption, refractive index issues, etc.) = %
Light absorption (?)
Absorbs: % of the incoming photons above its band gap
Bottom cell for tandem device
Parasitic light loss (catalyst or proteciton layer absorption, refractive index issues, etc.) = %
Light absorption from bottom cell (if a tandem device) (?)
Absorbs: % of the incoming photons above its band gap
The user should consider any parasitic light absorption from the top cell at photon energies below the band gap and adjust the bottom cell absorption % to compensate.
(A simple UV-Vis of the top photoabsorber can determine parasitic absorption.)
The file should contain
only 2 columns with no headers.
Column 1 should be the wavelength (nm) and column 2 should be the
Absorbance. (Absorbance is a unitless value. Even though Wikipedia says that Absorbance can in the units of 'A.U' for absorbance units, this is just garbage.
'Absorbance units' was just a cover for people who errently thought Absorbance was just an arbitray number. Rant over.)
Scan rate does not matter.
'incoming' is defined as only the photons that have already made it past any water layer that may be present. If photon matching is used
the absorption percentage may decrease if the large band gap needs to be thinned down to allow more light penetration to the small band gap material.
This is only relevant for tandem devices or situations in which the user uploads a large band gap photoabsober. 'incoming' is defined as only the photons that have already made it past any water layer that may be present and past the photoabsorber #1 .
If photon matching is used this value corresponds to an absolute absorption percentage of incident above band gap photons rather than a pro-rated absorption percentage.
The band gap of the
photoabsorber used in the CV is: mV
The photoelectrode in the CV is the:
The photoelectrode in the CV is doing a/an
Select the .csv file that contains the CV of the
photoelectrode (formatting):
--Here is an example file of a Si photocathode data file based very roughly on the work by Seger et.al, JACS, 2014--
The file should contain
only 2 columns with no headers.
Column 1 should be the voltage (V) and column 2 should be the
current in (mA/cm2).
The file should be only a single linear sweep across the voltage
range.
Scan rate does not matter.
The voltage should be versus the redox reaction being done (i.e.
(vs. RHE) for H2, vs (1.23 V vs RHE) for O2
evolution).
Voltage example: if one is operating at 0.8V vs. RHE for O2
evolution, this would need to be inputted as +0.42 V.
When it doubt about the voltage sign, more positive voltages are
good, negative voltages are bad.
The voltage needs to be in ascending or descending order (thus 0.1, 0.2. 0.3 V) not (0.1, 0.3, 0.2 V). Very rarely should this ever be an issue.
The sign (+/-) of the current does not matter. The program takes
the absolute value of the current.
If your CV slightly crosses over the 0-current axis, these
points will be cropped out/eliminated. (This is done by
eliminating all points that do not have the same sign as the
maximum)
The programs assumes the file is done under AM1.5 light.
The program also assumes any losses due to ion transfer have been compensated for
Water primarily absorbs in the low band gap
regime. Thus the user should make a educated decision when
setting the water absorption depth with respect to their
experiment and the band gap of their photoabsober.
Photovoltage
Dark saturation current (mutiple of theoretical
minimum) (?): x
The minimum
theoretical dark saturation current (io, theory) is
a function of band gap, temeparture as given by : Martin A.
Green "Third Generation Photovoltaics" (Springer, Heidelberg
2003) page 38. This multiplier will take io, theory
and multiply it by whatever constant is set here.
Example: if the calculations determines io, theory
for a 1.0 eV band gap mateial is 10-11 mA/cm2
and the multiplier is 100, the program will use a io=10-9
mA/cm2
Determine dark saturation current through a set open circuit value This approach is based off of the work from Seitz et al. ChemSusChem, 2014
Assume the open circuit voltage of the photoabsorber has a band gap of mV less than the band gap. The program will then calculate a dark saturation current based off of this value.
Shunt resistance Ohm x cm2
Series resistance Ohm x cm2 Force a set fill factor (by modifying the series resistance)
Force a fill factor value of % for each photoabsorber
Force a tandem solar cell fill factor value of %
The tandem solar cell approach is based off the work of Hu et al., 2013, Energy & Environmental Science. The maximum fill factor is limited by bandgap. If the set fill factor is greater than the maximum theoretical fill factor, the program will leave this point blank since it is unfeasible.
This approach is based of the work of Hu et. al, Energy & Environmental Science, 2013
--This assumes equal
molar concentration of reactants and products-- Enthalpy of
reaction kJ/mol
Entropy of reaction J/(mol K)
Number of electrons transferred per reaction
Faradaic efficiency = %
Calculate production rates (mol/m2/hr) instead of efficiency
The reaction product is a electron redox process.
Reduction
Overpotential
There
should be no reduction overpotential since the user generated CV
has taken this into account (unless the CV is a pure
photovoltaic)
Overpotential from
the
reduction reaction mV
Select the .csv file that contains the linear sweep of the reduction reaction (formatting):
--Here is an example file of low loading (200ng/cm2) Pt for H2 reduction based on the electrocatalyst used in the work from Kemppainen et.al, EES, 2015--
The file should contain
only 2 columns with no headers.
Column 1 should be the overpotential (in mV) and column 2 should be the
current in (mA/cm2).
The file should be only a single linear sweep across the voltage
range.
Scan rate does not matter.
It does not matter whether the current is positive or negative.
The program interpolates data, but does not extrapolate the i-V curve.
Tafel slope for
reductive
reaction mV/decade
Exchange current density mA/cm2
Overpotential at 1 mA/cm2 mV
Tafel slope for reductive reaction mV/decade
Oxidation Overpotential
There
should be no oxidation overpotential since the user generated CV
has taken this into account (unless the CV is a pure
photovoltaic)
Overpotential from
the oxidation reaction mV
Tafel slope for
oxidative reaction mV/decade
Exchange current density mA/cm2
Overpotential at 1 mA/cm2 mV
Tafel slope for oxidative reaction mV/decade
The file should contain
only 2 columns with no headers.
Column 1 should be the overpotential (in mV) and column 2 should be the
current in (mA/cm2).
The file should be only a single linear sweep across the voltage
range.
Scan rate does not matter.
It does not matter whether the current is positive or negative.
The program interpolates data, but does not extrapolate the i-V curve.
Ionic Losses
Ionic loss between
anode and cathode mV
Ionic conductivity
mS/cm
Average ionic path length cm
Elecrolyte
Concentration (molarity)
Electrolyte Temperature
These values are only valid at 25C, thus they will not be correct for your calculations. Ionic conductivity is highly tempearture dependent.
Ensure that your ionic conductivity tempearture matches your reactor tempearture since ionic conductivity is highly tempearture dependent.
Average ionic path
length cm
Precision and Plotting Options:
Precision Options
If you set the values too accurate or precise you may freeze your
computer for a little bit (or longer), while it is doing the
calculations.
The program calculates efficiencies conservatively (via iteration process), thus increasing the precision may yield a slight increase in efficiency.
Precision Efficiency
Current step size (?):
in
µA/cm2
The program iterates
through current to find the maximum current/efficiency for the
device. This is how big the step size is between iterations.
Photoabsorbers
If you are using 'Add new line...' or 'Subtract from previous graph...' you can not change your step size
Top cell photoabsorber band gap range: From meV
to meV
with data points every: meV
Bottom cell photoabsorber band gap range:
From meV to meV
with data points every: meV
i-V curve
For each band gap an i-V curve is made and then the voltage is varied
to find the maximum current (and hence efficiency) for a given reaction.
Current precision in i-V curve: ( x Current step size) in µA/cm2
Voltage precision in i-V curve: in mV
This uses the light concentration, water absorption, photoabsorber absorption (from top cell), dark saturation current (multiple of theoretical minimum), series and shunt resistance
to create an i-V curve.
Plot Options
Options for Single Photoabsorber and Plots involving User
Inputted Photoelectrode
Title: Title for photon matching / thinning top cell photabsorber:
Title Font Size:
X-Axis title:
Y-Axis title:
Font size of axis title:
X-Axis tick spacing: eV
Y-Axis tick spacing: %
Tick Font Size:
The smoothing factor just
makes the graph look good. It does not effect the calculate
efficiencies at all. Between 0-1 is suggested, but it possible
to go to higher values.
Note: that the x and y-axis will be set by the band gap range
Fix set values for contour plot
This allows for you to add an extra trace to the graph (x-y plot) or subtract from a previous graph (for contour plots)
This either adds or subtracts data to the previous data set irrespective of whether it is on Panel 1 or Panel 2
It is however possible to create new data on one panel and subtract this new data from the previous data on the other panel.
Photon-Driven Nitrogen Fixation: Current Progress, Thermodynamic Considerations, and Future Outlook
Medford A.J. ; Hatzell M.C. ACS
Catalysis 2017 7 (4), 2624–2643 doi: 10.1021/acscatal.7b00439
A
Flexible Web-Based Approach to Modeling Tandem Photocatalytic
Devices. Seger B.; Hansen, O.; Vesborg P.C.K. Solar
RRL 2017 1, 1600013. doi: 10.1002/solr.201600013
Vesborg
P.C.K.; Seger B. Performance Limits of Photoelectrochemical CO2
Reduction Basedon Known Electrocatalysts and the Case for
Two-Electron Reduction Products Chemistry
of Materials 2016, 28, 8844−8850. doi:10.1021/acs.chemmater.6b03927
Mei
B.; Mul G.: Seger B. Beyond Water Splitting: Efficiencies of Photo-Electrochemical Devices Producing Hydrogen and Valuable Oxidation Products Advanced Sustainable Systems
2017 1, 1600035. doi:10.1002/adsu.201600035