1. Journal Name
ARTICLE
This journal is © The Royal Society of Chemistry 20xx Y. Morjaria, 2013, 00, 1-3 | 1
a.3rd Year Undergraduate Laboratory, Department of Chemistry, University of
Warwick, CV4 7AL. E-mail: Y.Morjaria@warwick.ac.uk
†
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here].
http://moodle.warwick.ac.uk/mod/assign/view.php?id=116107
Date Submitted: 08/05/15
Dye- sensitised Solar Cells Manufactured with Berries
Y. Morjaria,a*
M. Kharelb
DSSC’s can be formed from anthocyanins extracted from berries. In this report the performance characteristics of
blackberries, raspberries and blueberries were investigated over time . Blackberries produced the greatest power
therefore were further tested with variable pH’s and operating temperature. Slightly acidic conditions were proven to be
optimal whiilst a higher operating temperature reduced effiency. Furthermore an example of the impact porosity has on
cell performance was reinforced using a planar electrode.
Introduction
The increasing energy demand in the developing world, combined
with diminishing fossil fuel resources, has placed a greater
emphasis on the development of renewable energy sources. Dye-
sensitised Solar Cells (DSC’s) are a type of third generation
photovoltaic cell which convert light energy into electrical energy.
DSC’s are a promising technology in the development of solar cells
with light-to-electrical energy conversion reaching up to 11%1,
providing an alternative to more common silicon based
photovoltaics. Ruthenium based complexes are currently the most
popular sensitising dyes however to create more cost effective
DSC’s; solution processable organic dyes are being tested.
Anthocyanins are a group of molecules found naturally that
demonstrate optical and structural potential as a dye. Within this
report the structural and electrical functionality of anthocyanins,
extracted from berries, as light harvesting molecules, will undergo
investigation.
Theory
DSC’s are multilayer devices, formed by chemical adsorption of an
organic sensitising dye onto a wide band gap semiconductor, most
commonly mesoporous TiO2. An electrolyte solution is applied
before a conductive glass counter electrode is then bound upon the
dye layer. Upon illumination the sensitising dye absorbs a photon
causing photoexcitation of an electron from the HOMO to the
LUMO of the dye. Rapid electron injection takes place from the dye
LUMO into the conduction band of the semiconductor. Diffusion
through TiO2 allows the electron to be delivered to an electrode,
through the external load and eventually the counter electrode,
creating a current. The oxidised dye is reduced by the electrolyte
solution to regenerate the dye where the electrolyte diffuses to the
counter electrode to be reduced (fig.1). The reaction is
thermodynamically driven; following a potential gradient
throughout the circuit. Cell performance is based upon the
manipulation of these energy levels to increase rate of electron
transfer. By increasing the kinetic rate of favourable processes, such
as photoexcitation from the HOMO to LUMO, whilst reducing the
rate of unfavourable processes i.e. TiO2/Dye Recombination, a
better power efficiency can be obtained.
Figure 1: Schematic representation of DSC operating principles. Adapted
from Holmber, Perenikovsy, Kulinksy and Madou2.
Anthocyanins belong to the molecular group flavonoids and can
behave as chromophores making them viable as a DSC dye. They
contain a benzopyrilium ring and differ by the position of the
hydroxyl and methoxyl groups within the structure (fig.2). At very
high or very low pH levels the equilibria between the deprotonated
and protonated forms is disturbed causing the wavelength (λ)
absorbed to change. This impacts photoexcitation as the
wavelength absorbed is relative to the HOMO-LUMO band gap.
Secondly, when basic, the anchoring ability of the dye to the TiO2
can be compromised creating inefficient contact and therefore
poorer quantum efficiency of electron injection. Proton adsorption
can lead to a positive shift in TiO2 Fermi level resulting in a weaker
potential gradient being present and therefore reduced voltage.
Increases in the anchoring group length slow the kinetic rate of
electron transfer therefore reduce the photocurrent observed.
Multiple hydroxyl binding groups allow for chelation of the
anthocyanins onto the metal where in acidic conditions, in
deprotonated form, the binding is stronger therefore greater
stability and device efficiency is present.
Experimental
Preparation of Dye solutions from Berries
Blackberries, Blueberries and Raspberries were individually crushed
using a pestle and mortar and minimal amount of ethanol to form a
paste. Solid particulates were separated from the paste using a
centrifuge at 1000rpm for 5 minutes. The supernatant was
syphoned off and underwent centrifugation once more to remove
all solids. A UV/Vis was taken of the resulting berry extract, diluting
100µm of centrifuged dye in 3cm3 of water.
 Raspberry- Absorbance: 0.322, Wavelength: 519.00nm
 Blackberry- Absorbance: 0.540, Wavelength:519.00nm
 Blueberry- Absorbance: 0.113, Wavelength:517.00nm

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2 | Y. Morjaria., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx
Figure 2: pH dependency and chelation of anthocyanins. Adapted from
Etula3.
The wavelength recorded corresponds to the HOMO-LUMO band
gap; assuming that the anthocyanins in the extracted dye are solely
responsible for the absorption peak and no other organic molecule
considered, e.g. pectin [3]. By conversion of the wavelength to eV
the band gap for each berry is known. Using the Beer-Lambert Law
(equation 1) where A is Absorbance, Ɛ is molar extinction coefficient
measured in Lmol-1, C is concentration, Moldm-3 and L is length cm.
The concentrations were standardised through dilution to attain the
same absorbance values at 515nm.
(1) A= ƐCL
Concentrating the dye extract could not be carried out by
evaporating ethanol as anthocyanins degrade at temperatures
lower than the boiling point of ethanol4(78.37*c). Also some
ethanol soluble anthocyanins may boil off with evaporation.
Fabricating the electrodes Plates
The planar TiO2 electrode was fabricated by spin casting a prepared
1:5 solution of Titanium (IV) isopropoxide: butanol onto a clean
glass substrate at 1000rpm. Then annealed at 300 °C for 1 hour.
Meso-porous TiO2 coated electrodes provided were heated on a hot
plate at 300 °C for 10 minutes to fabricate. The counter electrodes
were produced by applying a layer of graphite, using a pencil, onto
the conductive side of a SnO2 conductive plate. The conductive
plate was then annealed at 300 °C for 5 minutes. All plates were left
to cool following annealing.
Device Assembly and measurements
6 drops of anthocyanin solution was pippeted onto the TiO2 film
side of an electrode and left to stain for 15 minutes. The stained
electrode was then washed with water followed by ethanol and
blotted dry. One drop of 0.1M K/I3
- electrolyte solution was applied
to the dye sensitised face of the TiO2 electrode and the graphite
face of the counter electrode was place on top.
Figure 3: Experimental setup for measuring current-voltage
The electrodes were offset and bound together by bulldog clips. A
circuit was constructed as shown in Figure 3 involving; the DSC, a
50W Lamp maintained at a constant position from the cell at all
times and a resistor. The current- voltage readings were taken for
all DSC’s made, using the multimeters provided immediately after
assembly and then at various intervals from 0 to maximum. All 3
berries were individually applied upon a meso-porous TiO2 DSC
whilst only the blackberry dye was applied to a planar TiO2. The
device area exposed was measured in order to calculate current
density and power efficiency.
Testing the effect of pH on DSC’s
3 DSC cells were constructed to investigate the effect of pH on cell
performance all using the blackberry dye. 2 involved changing the
pH of the blackberry dye from pH 3-4 to neutral 7-8 and another
from pH3-4 to pH9-10. The dyes were then applied and DSC’s
assembled and tested as above. Another test devised was applying
dilute acid to the meso-porous TiO2 layer prior to assembly to test
the effects upon the anchoring groups at the interface.
Testing device stability of DSC’s
Testing heat effects on stability involved a blackberry dye DSC being
constructed and placed in the oven away from light at 40°C for 10
minute intervals before being tested. The device was allowed to
cool down before a second current voltage measurement was taken
before returning the DSC to the oven. To test light factors on device
stability a blackberry dye DSC was placed under a lamp however
between readings was covered by a 3 layers of foil to prevent heat
degradation and block out all light.
Results and discussion
Power Conversion Efficiency
Power conversion efficiency (η) can be calculated using the
following equations; involving Power input (Pin) Short circuit
current (Jsc), open circuit voltage (Voc) and the maximum power
points (mpp) for each parameter respectively:
(2) 𝛈 =
𝑽𝒐𝒄 𝒙 𝑭𝑭 𝒙𝑱𝒔𝒄
𝑷𝐢𝐧
Where Fill Factor, FF is:
(3) 𝑭𝑭 =
𝑱𝒎𝒑𝒑𝒙 𝑽𝒎𝒑𝒑
𝑱𝒔𝒄𝒙𝑽𝒐𝒄
Table 1 displays summarises the power conversion efficiencies of
the 3 berries used. The overall low efficiencies can be contributed
to purity of the anthocyanins extracted and dilution of the
solutions. The blackberry had the greatest efficiency amongst the
meso-porous DSC’s. This can be attributed to a better quantum
efficiency being present. With reference to figure 1, the electron
affinity of raspberries and blueberries is greater than blackberries
causing a HOMO-LUMO energy levels to increase therefore more
energy required for photoexcitation to take place. This is supported
by the initial UV/Vis absorbance observed where blueberry and
raspberry have weaker absorbance likely due to more electron
withdrawing groups being present which increase binding energy
and therefore ionisation potential. Although the weaker
absorbance’s can be attenuated to weaker concentration this would
also reduce efficiency, as even after dilution the blackberry extract
is likely to contain less impurities which may bind to TiO2 surface
preventing efficient electron injection. This would likely decrease
the Fermi level, increasing TiO2/ dye recombination. It was

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This journal is © The Royal Society of Chemistry 20xx Y. Morjaria., 2013, 00, 1-3 | 3
hypothesised that the raspberry would be more efficient that
results displayed and should be noted scratches on the TiO2 coated
surface may have contributed to this result. Natural photosynthesis
has a conversion of <6% [5]. This is due to harvesting a larger
proportion of the visible spectrum, visually identified by the green
colour chloroplasts and plants emit. Commercial photovoltaics have
an efficiency of 24% [6] where they can absorb wavelengths of up to
950nm creating a stronger photocurrent. They have a direct band
gap which is better at light capturing than DSC’s where energy is
wasted, albeit necessary, in over-potential. Voc can be significantly
increased through doping allowing more freedom than the
currently designed TiO2 present in DSC’s.
Table 1: Maximum power efficiency for berry DSC’s calculated
Fabricated DSC Maximum Power
Efficiency (η ) (%)
Time Elapsed
from DSC (mins)
Meso-porous blackberry 0.01 0
Meso-porous blueberry 0.0013 35
Meso- porous raspberry 0.0017 0
Planar blackberry 0.0000021 0
The planar blackberry cell only had dye adsorbed to its surface, an
area 3.915cm2, whereas the meso-porous electrode had a surface
area of 5m2 significantly greater. As a result the amount of dye
adsorbed is far greater allowing a greater photocurrent to be
produced.TiO2/dye recombination become more significant as
contact points are fewer causing a decrease by ~x10-4 in efficiency.
This demonstrates the dependence of power efficiency on total
surface area present.
Current-Voltage Parameters with Time
The effect of time on the current-voltage characteristics is displayed
below. The Jsc of the blackberry was greatest however decreased
over time which could be a result of aggregation of the
anthocyanin’s upon the electrode surface creating poorer electron
injection from dye LUMO- TiO2 CB as greater resistance is present.
The blueberries show approximately a 50% increase in Jsc. Possible
better anchoring of the dye increasing the rate of electron transfer
from dye to CB as the molecule reaches an equilibrium in structure.
Heat from the lamp overtime increased providing energy to help
photoexcitation and increase mobility of electrons which translates
to a higher current for blueberries. The low current of blueberry
and raspberry indicates the over potential between LUMO-CB is
very small reducing the the thermodynamic driving force behind
electron transfer, causing less electrons to be delivered to the
external load.
Figure 5 (above) showing the Jsc (A/cm2) and Figure 6 (overleaf) Voc (mV)
over time for the 3 sensitising dyes.
As shown above the open circuit voltage, at which current is zero,
remains a relative constant amongst all three berry cells tested over
time. This indicates there is little change in the redox potential of
the Fermi level in the TiO2 relative to the counter electrode over
time. Changes seen in the power conversion efficiency over time
are likely to be triggered by Jsc changes. Blackberry exhibits a
greater Voc due to larger population of electrons in TiO2 causing an
upward shift in the Fermi level comparable to raspberry and
blueberry. The Voc has a strong correlation with the strength of
adsorption as this contributes to the diffusion pathway of an
electron. The blueberry stained electrode did not exhibit a strong
colour as did the other two which may be a reflection on its
adsorption ability reflected in the graph above.
Effect of pH on Device Performance
Performance is dependant by pH levels as displayed in Table 2. For
blackberry DSC the device performance is reduced across the pH’s
of 3, 7 and 11 of the staining dye. The blackberries natural pH level
was 3-4 and therefore slightly acidic. In this form the anthocyanin’s
present exist as flavilium ion (see fig.2) which can chelate to Ti+4
through deprotonated hydroxyl groups and more strongly. As the
solution is made more basic the hydroxyl groups present in the
anthocyanin’s become more hydrated and possibly lost as the
quinonoidal base forms as equilibria shifts [7]. As a result only
monodentate binding can occur reducing the anchoring strength of
the dye and proximity to the electrode. This reduces the cell
efficiency as the diffusion pathway is increased so kinetically the
electron takes more time to be delivered to the external circuit. As
quantum efficiency is negatively impacted the overall effect is a
decrease in cell performance as the pH level is increased. This was
further supported by the colour of the dye across the 3 solutions
made. The flavilium form exhibited a strong red colour whilst upon
increasing the pH the colour progressively weakened to light pink as
equilibria favoured, the poorer light harvesting, quinonoidal form of
the anthocyanin. Although a UV/Vis was not taken for each solution
I would have expected the wavelength absorbed to decrease in
length as the reduction in conjugative ability of the molecule is
reduced, resulting in a larger band gap required for photoexcitation.
A second investigation of pH was conducted in which the TiO2
electrode was treated through being washed with dilute acid.
Anthocyanins bind to the electrode surface by deprotonation of the
hydroxyl group allowing negatively charge oxygen atom to form a
dative covalent bond. It is thought hydrogen is delivered to outer
sphere ligands on the Ti+4. The pre-treatment process allows a layer
of protons to adsorb onto the electrode surface which significantly
inhibits the anchoring ability as the proton transfer step less
favourable charge interactions. It was expected that the cell
0.0
100.0
200.0
300.0
400.0
500.0
600.0
0 20 40
Jsc(mA/cm2)
Time (minutes)
Blackberry
Raspberry
Blueberry
0
50
100
150
200
250
300
350
400
0 10 20 30 40
Voc(mV)
Time (minutes)
Raspberry
Blueberry
Blackberry

4. ARTICLE Journal Name
4 | Y. Morjaria., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx
Table 2: Power efficiency of pH adjusted DSC’s and calculation parameters
performance would be reduced and this was observed. However
overtime power conversion efficiency improved from 0.0032% to
0.0064%. A primary reason for this is an equilibria being reached as
the dilute acid interacts with the electrolyte solution where
desorption of the protons from the TiO2 surface will occur. This will
allow the anchoring anthocyanins to bind better to the surface and
increase the likeliness of multidentate binding occurring which
results in faster electron injection. Consequentially the Jsc
increased over time creating better performance of the cell. Whilst
it was expected that the Voc would increase over time as proton
desorption would increase the Fermi level in the conduction band,
this was not observed. A possible explanation is that as equilibria
shifts, to neutralise the surface, the protons released increase the
kinetic rate of recombination factors as a trade-off despite this
improving surface interactions. It can be proposed from this
experiment that a hydroxide wash may yield higher power
efficiency.
Effect of Temperature on Device Performance
Through storing our device within an oven at 40°C where
measurements were taken every 10 minutes, both a cold reading
and a hot reading. It was hypothesised that the cold reading would
produce poorer efficiency and reduction in Voc and Jsc parameters
however results were very similar to the hot reading and therefore
have not been included in analysis. The initial reading of Jsc upon
fabrication was very low, due to scratches present on the
conductive surface. These covered approximately 10% of the device
and led to initial Jsc reduction of 550 to 71.7µA/cm2 leading me to
believe experimental error was involved. The heated device showed
a steep increase in Jsc the longer it was heated for (fig.7). As the
sensitising dye was organic this would increase the thermal energy
thus increasing the probability of photoexcitation. The electron
injection process is thermodynamically driven therefore an increase
in thermal energy would drive this reaction. Furthermore, the rate
of diffusion would be increased as mobility is greater
consequentially increasing conductivity. Overall this leads to great
quantum efficiency which explains the increase in performance
over time.
Figure 8: Trend in Jsc over time left in oven at 40°C.
Over Voc values slightly increased overtime following an initial
decrease in voltage likely due to the quasi Fermi level equilibrating.
As a result the overall increase in device performance can be
attributed to the increase in current which a higher operating
temperature incites. At higher temperature I would expect poorer
device stability as anthocyanins are volatile and the kinetic rate of
degradation would increase at temperatures of 50 °C and above.
Conclusion
Whilst in photovoltaic technology a compromise between current
and voltage is required for greater performance, through data
analysis it seems Jsc has a stronger correlation to device efficiency
than Voc for the devices fabricated. It is also evident that when
constructing DSC’s numerous factors must be considered such as
electrolyte used, dye extraction methods, oxygen atmosphere all of
which contribute to the key process such as electron injection or
device stability. From the data a possible optimal temperature
between 20-40 degrees Celsius is likely where performance can be
significantly improved. Also it is evident that anthocyanin dyes
exhibit far greater absorbance and device efficiency in an acidic
environment than a basic one. Furthermore the investigation
concludes that surface interactions of the dye and electrode is
critical shown by the acid wash experiment as this affects the
kinetic rate of electron transfer. Such devices show great promise
with their cost effective manufacturing and ability to utilise a range
natural resources that will allow the efficiency to be continually
improved through further investigation of potential dyes and
knowledge of contributing factors.
Acknowledgements
I would like to acknowledge Manish Kharel as my lab partner, always
by my side, as we conducted this investigation.
Notes and references
‡ Data for the light factor controlled cell displayed highly anomalous date and
therefore has been omitted from this report. Investigation was carried out on
Quercetin, a synthetic dye, which proved unreliable due to inefficient staining
times and therefore has been omitted.
[1] Francesco Ambrosio, Natalia Martsinovich, Alessandro Troisi, J. Phys. Chem.,
2012, 116,2622-2629
[2] Sunshine Holmberg, Alexandra Perebikovsky, Lawrence Kulinsky, Marc Madou,
Micromachines, 2014, 5(2),171-203
[3] Jarko Etula, Opean Journal For Young Scientists and Engineers, 1, 2012.
[4] G. Smestad, 1998. Solar Energy Materials and Solar Cells, 1998, 55, 157-178.
[5] A. Hagfeldt and M. Grätzel. Acc. Chem. Res., 2000, 35, 269.
[6] B. E. Hardin, H. J. Snaith, M. D. McGhee, Nature Photonics, 2012, 6, 162.
[7] A. Melis, J. PlantSci., 2009, 177, 272-280.
pH
environment
Jsc
(µA/cm2)
Voc(mV) Fill
Factor
Power
conversion
efficiency
(%)
Time
(mins)
3.5 550 362.2 0.2450 0.01 0
7.5 392.7 251 0.2466 0.0051 25
9.5 445.9 239.3 0.2020 0.0048 25
Acid washed
electrode
372.1 292 0.2864 0.0065 25
0.0
100.0
200.0
300.0
400.0
500.0
0 20 40 60
Jsc(mA/cm2)
Time (minutes)
Heat
0
100
200
300
400
0 10 20 30 40 50
Voc(mV)
Time (minutes)
Heat
Figure 8: Voc over time of heated cell.

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