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Investigating the Recycling Potential of Glass Based Dye-Sensitized Solar Cells—Melting Experiment


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The effects of climate change are becoming increasingly clear, and the urgency of solving the energy and resource crisis has been recognized by politicians and society. One of the most important solutions is sustainable energy technologies. The problem with the state of the art, however, is that production is energy-intensive and non-recyclable waste remains after the useful life. For monocrystalline photovoltaics, for example, there are recycling processes for glass and aluminum, but these must rather be described as downcycling. The semiconductor material is not recycled at all. Another promising technology for sustainable energy generation is dye-sensitized solar cells (DSSCs). Although efficiency and long-term stability still need to be improved, the technology has high potential to complement the state of the art. DSSCs have comparatively low production costs and can be manufactured without toxic components. In this work, we present the world’ s first experiment to test the recycling potential of non-toxic glass-based DSSCs in a melting test. The glass constituents were analyzed by optical emission spectrometry with inductively coupled plasma (ICP-OES), and the surface was examined by scanning electron microscopy energy dispersive X-ray (SEM-EDX). The glass was melted in a furnace and compared to a standard glass recycling process. The results show that the described DSSCs are suitable for glass recycling and thus can potentially circulate in a circular economy without a downcycling process. However, material properties such as chemical resistance, transparency or viscosity are not investigated in this work and need further research.
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Materials 2021, 14, 6622.
Investigating the Recycling Potential of Glass Based
Dye-Sensitized Solar CellsMelting Experiment
Fabian Schoden 1,*, Anna Katharina Schnatmann 1, Emma Davies 1, Dirk Diederich 2, Jan Lukas Storck 1,
Dörthe Knefelkamp 1, Tomasz Blachowicz 3 and Eva Schwenzfeier-Hellkamp 1
1 Institute for Technical Energy Systems (ITES), Bielefeld University of Applied Sciences, 33619 Bielefeld,
Germany; (A.K.S.); (E.D.); (J.L.S.); (D.K.); (E.S.-H.)
2 Institut für Glas- und Rohstofftechnologie GmbH, 37079 Göttingen, Germany;
3 Institute of PhysicsCenter for Science and Education, Silesian University of Technology, 44100 Gliwice,
* Correspondence:; Tel.: +49 521106-7386
Abstract: The effects of climate change are becoming increasingly clear, and the urgency of solving
the energy and resource crisis has been recognized by politicians and society. One of the most im-
portant solutions is sustainable energy technologies. The problem with the state of the art, however,
is that production is energy-intensive and non-recyclable waste remains after the useful life. For
monocrystalline photovoltaics, for example, there are recycling processes for glass and aluminum,
but these must rather be described as downcycling. The semiconductor material is not recycled at
all. Another promising technology for sustainable energy generation is dye-sensitized solar cells
(DSSCs). Although efficiency and long-term stability still need to be improved, the technology has
high potential to complement the state of the art. DSSCs have comparatively low production costs
and can be manufactured without toxic components. In this work, we present the world s first
experiment to test the recycling potential of non-toxic glass-based DSSCs in a melting test. The glass
constituents were analyzed by optical emission spectrometry with inductively coupled plasma
(ICP-OES), and the surface was examined by scanning electron microscopy energy dispersive X-ray
(SEM-EDX). The glass was melted in a furnace and compared to a standard glass recycling process.
The results show that the described DSSCs are suitable for glass recycling and thus can potentially
circulate in a circular economy without a downcycling process. However, material properties such
as chemical resistance, transparency or viscosity are not investigated in this work and need further
Keywords: recycling; circular economy; dye-sensitized solar cell; glass recycling; ICP-OES;
SEM-EDX; melting experiment
1. Introduction
An important pillar against climate change is the transformation of the energy sector
to 100% renewable energy [1]. However, the energy sector is not the only contributor to
climate change. Another critical problem is the consumption and depletion of resources
and our linear economy, which is a cause of extensive carbon emissions [2,3]. The concept
of how the linear economy works is often described as take, make, waste [4]. Resources
are mined or extracted, then processed into products that are sold, used and usually dis-
posed of after a few weeks or months [5].
Citation: Schoden, F.; Schnatmann,
A.K.; Davies, E.; Diederich, D.;
Storck, J.L.; Knefelkamp, D.;
Blachowicz, T.; Schwenzfeier-
Hellkamp, E. Investigating the
Recycling Potential of Glass Based
Dye-Sensitized Solar CellsMelting
Experiment. Materials 2021, 14, 6622.
Academic Editors: Marek Lipiński
and Andrea Petrella
Received: 23 September 2021
Accepted: 29 October 2021
Published: 3 November 2021
Publisher’s Note: MDPI stays neu-
tral with regard to jurisdictional
claims in published maps and institu-
tional affiliations.
Copyright: © 2021 by the authors. Li-
censee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and con-
ditions of the Creative Commons At-
tribution (CC BY) license (http://crea-
Materials 2021, 14, 6622 2 of 18
Therefore, the need for sustainable and recyclable renewable energy systems is be-
coming increasingly important [6]. Technologies are needed that not only harness renew-
able energy but that can also be repaired, remanufactured and recycled [3]. One technol-
ogy that has great potential in this area is dye-sensitized solar cells (DSSCs) [7]. They can
be made from non-toxic material, and the production process is less energy-consuming
compared to silicon-based photovoltaics (c-Si PV) [811]. They can also be used in areas
with low light intensity, such as indoors or in the morning and evening hours [12]. This
means they are well suited to complement existing renewable energy technologies and
can be integrated into windows, facades or cars, even as transparent versions, and into
Internet of Things devices [13,14]. In addition, DSSCs are easy to manufacture and insen-
sitive to impurities, which facilitates industrial scale-up and enables manufacturing in ru-
ral areas [6,15].
The operating principle of a DSSC can briefly be described as follows: DSSCs consist
of two glass plates coated with fluorine-doped tin oxide (FTO). The FTO layer makes one
side of the glass plate conductive. The front electrode is additionally coated with a semi-
conductor, typically TiO2. A dye can be incorporated into the porous TiO2 layer. The coun-
ter electrode is coated with graphite or platinum in addition to the FTO layer. The front
and counter electrodes are connected by an electrolyte. When light excites the dye, elec-
trons are released from the dye and transported through the TiO2 layer into an external
circuit where the current can be used. The electrons enter the DSSC through the counter
electrode and recombine with the acceptors of the electrolyte, reducing the electrolyte,
which eventually leads to the reduction of the dye cation. The role of the graphite or plat-
inum layer on the counter-electrode is that of a catalyst, allowing the electrons to make
their way through the electrolyte to the TiO2 layer and complete the circuit [1618].
So far, DSSCs are not ready for mass production, and industrial scale-up depends on
further improvement of DSSC efficiency and long-term stability. The highest efficiencies
for DSSCs are achieved by using toxic or scarce materials such as silver, cobalt, platinum
and ruthenium dyes [13,19]. This type of DSSC achieves efficiencies of over 14% in labor-
atory tests [15]. In ambient light, Freitag et al. achieved a power conversion efficiency
(PCE) of 28.9% [20]. DSSCs, based on non-toxic and abundant components, usually use
plant dyes such as carotenoids, chlorophylls or anthocyanins [21,22]. The efficiency of
such DSSCs is usually less than 1% [2325]. Innovations in DSSC research are also likely
to rely on organic dyes, not just natural dyes. However, organic dyes can be toxic and thus
dangerous for the environment [26,27]. This could make a recycling process more compli-
cated. Some natural dyes require solvents and energy for the purification process, similar
to ruthenium dyes [28]. Organic or natural dyes for DSSC applications should be devel-
oped following the twelve principles of Green Chemistry [13,29].
Long-term stability can be improved by using gel or solid-state electrolytes [10,30,31].
However, long-term stability research is often avoided because time-consuming tests are
required to evaluate stability, and this creates a conflict with respect to rapid publication
[32]. Gel electrolytes can improve long-term stability, and the DSSCs are stable for at least
140 days [33]. Plastics such as polyacrylates or polyacrylonitrile are used in gel electrolytes
and could hinder the recycling process due to their poor biodegradability [34,35]. When
these plastics enter the environment and become microplastics, they can enter the food
chain and harm organisms [36].
To improve energy conversion and reduce cost, quantum dots are used to fabricate
quantum dot sensitized solar cells (QDSC) [37]. These QDSCs could potentially be sub-
jected to a similar recycling process as glass-based DSSCs. However, the basic elements of
the quantum dots are cadmium (Cd), lead (Pb) or other heavy metal compounds, which
are themselves toxic [38,39].
For DSSCs to be competitive on the mass market, they need to have a lifetime of up
to 5 years for textiles or similar wearable technologies [40]. For applications in or around
the building, a lifetime of about 25 years must be achieved to compete with c-Si PV [41].
Materials 2021, 14, 6622 3 of 18
In 2019, the global DSSC market size was USD 90.5 million, and the compound an-
nual growth rate for DSSCs from 2020 to 2027 is estimated at 12.4% [7]. DSSCs are a grow-
ing market, and according to several studies, the critical environmental factors of DSSCs
are [13,15,4143]:
The use of critical raw materials such as platinum and cobalt.
The drop in performance due to the instability of the electrolyte.
Uncertain waste management.
The high energy requirements in the production of transparent conductive oxide
(TCO) glass.
The last point, the high energy requirement for the production of TCO glass, results
from the life cycle analyses (LCA). In an LCA, the environmental impact of a product or
material is assessed. In these LCAs, the life cycle of the glass of the DSSC was considered
from cradle to grave [13,41,42]. Cradle-to-grave is the scope of LCA in this case, and envi-
ronmental impacts are considered from resource extraction to disposal of the DSSC. If a
cradle-to-cradle perspective were applied, i.e., the material is reused and recycled, the im-
pact, especially the energy demand, would be significantly reduced [44].
Therefore, in this experiment, we wanted to investigate the suitability of non-toxic
DSSCs with natural dyes for glass recycling. In the absence of experiments with practical
approaches to glass recycling and DSSCs, we conducted a melting experiment to investi-
gate possible solutions to close the loop. As part of the concept of a circular economy,
material cycles must be freed of toxic components. This means either recycling concepts
must be developed to separate toxic substances from the material loops or holistic design
principles must be applied. With the help of the circular economy, products are manufac-
tured that do not contain toxic substances and can therefore be recycled and reprocessed
more easily. This also eliminates the need for complicated separation processes for toxic
elements in material loops [3,4].
2. Materials and Methods
The glasses for the construction of DSSCs were purchased from Man Solar B. V. (Pet-
ten, The Netherlands). All glasses were coated on one side with FTO for conductivity. The
front electrode was additionally coated with TiO2 as semiconductor. Glasses from differ-
ent batches were investigated. Older glasses from 2018 were thin (40 mm × 20 mm × 2 mm,
4 g) and newer glasses from 2020 (40 mm × 20 mm × 3 mm, 6 g) were thick. From now on,
the thin glasses will be referred to as samples t1A and the thick glasses as t1B. In order to
perform this experiment within the framework of the circular economy school of thought,
DSSCs from old experiments with and without gel polymer electrolytes were used for the
melting experiment [45].
2.1. Investigating Glass Surface SEM-EDX
Scanning electron microscopy energy dispersive X-ray (SEM-EDX) measurement
was performed to investigate the surface of the glasses (Carl Zeiss EVO MA10, Carl Zeiss
AG, Oberkochen, Germany). In this method, a material is bombarded with electrons. If
such an electron hits electrons in deeper spheres of the bombarded sample, it is knocked
out of this atom. A vacancy in a lower atomic orbital causes an electron at a higher energy
level to jump to that lower energy level. In doing so, it emits characteristic X-rays. A
backscatter detector can be used to detect these X-rays. Since the energy of the X-ray beam
is material-specific, the element can be identified this way [46]. All scans were performed
with 20 keV accelerating voltage.
Samples t1A and t1B were split. One part of each sample was analyzed on both sides
in its original state, and the other part was etched with a mixture of concentrated hydro-
fluoric acid and concentrated sulfuric acid (mixing ratio 1:1) for 10 min and analyzed on
Materials 2021, 14, 6622 4 of 18
both sides by SEM-EDX. In addition, another part of sample t1B was etched with concen-
trated hydrofluoric acid for one minute and analyzed by SEM-EDX. The SEM-EDX anal-
ysis was performed according to DIN ISO 22309.
2.2. Investigating Glass Composition ICP-OES
In order to investigate the exact composition of the glass, optical emission spectrom-
etry with inductively coupled plasma (ICP-OES) was performed (ICP-OES Thermo Scien-
tific iCAP 6300 Duo, Thermo Fischer Scientific Inc., Waltham, Massachusetts, USA). The
samples were first dried and homogenized at 115 °C according to DIN 52331 with an oven
(Universal oven UF260, Memmert GmbH and Co. KG, Schwabach, Germany). Subse-
quently, the samples were analyzed by ICP-OES, according to DIN 51086-2. In this
method, the material is heated by an argon plasma, which has a temperature of about
10,000 K. The atoms in the vaporized sample are excited and emit material-specific elec-
tromagnetic radiation. This radiation can then be analyzed in a spectrometer [47].
2.3. Melting Experiment
Four melting tests were carried out. The adhesive film, which holds the DSSCs to-
gether, was removed manually from all DSSCs. To simulate a future glass recycling pro-
cess, each test batch consisted of 40% raw material and 60% cullet (glass intended for a
remelting process) from various sources. The raw material for glass production consists
mainly of silica sand and in smaller quantities of lime, ash, dolomite and soda ash [48].
The composition of the raw material mixture used in this experiment is shown in
Table 1.
Table 1. Composition of the used batch in weight percentage.
Calumite 2
Sodium Sulfate
Glassy calcium aluminum silicate produced from granulated blast furnace slag.
The first melt was the reference sample and consisted of a typical soda-lime-white
glass mixture (40%), as can be seen in Table 1 and white cullet (60%), hereafter referred to
as Melt A. The cullet used was a typical white container glass from a German processing
The second melt was also a typical soda-lime-white glass mixture, this time with the
addition of DSSCs (with glycerol and poly (ethylene oxide) (PEO), which were previously
built in 2020 and used as sample 1 in reference [45].
Regarding the applied simulated weathering process, the DSSCs of Melt B were
washed with tap water and then dried in the oven at 115 °C (Universal oven UF260, Mem-
mert GmbH and Co. KG, Schwabach, Germany).
The PEO served as a gel electrolyte in the DSSCs and helped to improve the long-
term stability of the DSSC. For future applications, the use of gel or solid-state electrolytes
could lead to unwanted plastic components in the melt, hereafter referred to as Melt B.
The third melt was a typical soda-lime-white glass mixture with addition of DSSCs,
namely, sample 2 from reference [45], with PEO and without simulated weathering pro-
cess, hereafter referred to as Melt C.
The fourth melt was a typical soda-lime-white glass mixture with addition of DSSCs
from unpublished experiments conducted in 2018, without PEO and without simulated
weathering process, hereafter referred to as Melt D.
The exact composition of the DSSCs of Melt B and C can be taken from reference [45].
Regarding Melt D, the DSSCs were also based on Man Solar glass slides and Mayfair-
forest fruit tea (Mayfair, Wilken Tee GmbH, Fulda, Germany) as a natural dye, but a com-
mercial liquid iodine-triiodide electrolyte purchased from Man Solar was used instead of
a gel electrolyte. Graphite was applied as a catalyzer layer by pencil (grade 6B, purchased
Materials 2021, 14, 6622 5 of 18
from J. S. Staedtler) and by graphite spray (Kontakt Chemie, Graphit 33). Their general
design is similar to that of the DSSCs used in reference [8,11].
Table 2 shows the estimation of the DSSC cullet composition (a detailed explanation
can be found in chapter 3.5Industrial Scale-Up and Volume Estimation).
Table 2. Estimated composition of the DSSC cullet in weight percentage.
FTO Glass
Table 3 shows the composition of the gel electrolyte of the cells used for the different
Table 3. Composition of the gel electrolyte of DSSCs used for the melting tests [45] in weight per-
600 kg/mol PEO
A (no electrolyte)
D (iodine/potassium iodide electrolyte)
Table 4 finally gives the overview of what each melt consisted of.
Table 4. Overview of the composition of each melt.
60% white cullet + 40% batch (Table 1)
60% DSSC cullet (Table 2) and electrolyte with PEO (Table
3/B) + 40% batch (Table 1)
60% DSSC cullet (Table 2) and electrolyte with PEO (Table
3/C) + 40% batch (Table 1)
60% DSSC cullet (Table 2) and electrolyte without PEO (Ta-
ble 3/D) + 40% batch (Table 1)
The DSSCs were crushed into pieces with a diameter of 0.8 mm using a hammer mill
(Mixer Mill MM 400, Retsch GmbH, Haan, Germany). Melting was performed at 1300 °C
for about 24 h in a furnace (laboratory chamber furnace-CWF, Carbolite Gero GmbH &
Co. KG, Hope, United Kingdom). During the melting phase and at the beginning of the
melting process, the state of the melts was visually observed and compared.
Three lab spatula of the material were added to the melting pots. After 5 min in the
furnace, the melts were visually evaluated and more material was added to the melting
pots (3 more spoonfuls of batch material). This procedure was repeated 20 min after the
start of the experiment and 50 min after the start of the experiment. After that, the melting
process was continued for 24 h.
After the melting test, the melts cooled and were examined with a microscope (Ste-
REO Discovery.V20, Zeiss AG, Oberkochen, Germany) according to ISO 8039.
3. Results and Discussion
3.1. SEM-EDX
Both electrodes are coated with FTO from one side, and the front electrode has an
additional TiO2 layer. This could be confirmed with the SEM-EDX. For both samples, a
surface with predominantly glass components could be detected. Figure 1a shows the
EDX spectrum of sample t1A. While C, Sn, Ti, O, Na and Si, as well as Al, indicate the
Materials 2021, 14, 6622 6 of 18
glass components in the deeper layers, Ti and Sn are the front layers indicating TiO2 and
Figure 1. SEM-EDX result for sample t1A, the TiO2-coated front electrode of a DSSC: (a) before etching; (b) after etching.
In Figures 1 and 2, the x-axis shows the energy of the X-rays emitted by the electrons
jumping to a lower energy level. In this way, conclusions can be drawn about the elements
of the sample. The y-axis shows the number of photons per second and electron volt
Very high concentrations of the element titanium and low concentrations of the ele-
ment tin were detected on the surface of sample t1A. Typical glass components could only
be detected in low concentrations.
Figure 1b shows the same sample after the etching process.
After the etching process, a significant decrease of the element titanium and a signif-
icant increase of the element tin could be determined. Elements typical for glass could be
determined in significantly higher concentrations after the etching process. This indicates
that the TiO2 layer on the glass surface can be removed with an etching process.
Figure 2a shows the EDX spectrum of sample t1B before the etching process. High
concentrations of the element tin as well as elevated glass-typical elements could be de-
termined. The glass-typical elements can be seen in the left part of Figure 2a.
Figure 2. SEM-EDX result for sample t1B, the FTO-coated back electrode of a DSSC: (a) before etching; (b) after etching
with hydrofluoric acid 1 min.
Materials 2021, 14, 6622 7 of 18
After the first 10 min etch with a mixture of hydrofluoric acid and sulfuric acid (1:1),
sample t1B showed no differences from Figure 2a. Therefore, a second etch with concen-
trated hydrofluoric acid was subsequently performed for one minute. The result can be
seen in Figure 2b. After both etching processes, an almost unchanged state of the glass
surface with high concentrations of tin and elevated concentrations of glass-typical ele-
ments could be determined. Table 5 provides an overview of the elements detected in the
SEM-EDX analysis.
Table 5. Overview of the elements detected with SEM-EDX.
Detected Elements
t1A before etching (Figure 1a)
t1A after etching (Figure 1b)
t1B before etching (Figure 2a)
t1B after etching (Figure 2b)
Even after the etching processes, Sn could still be measured for both samples. This
indicates incomplete removal of the layers present on the glass surface. However, TiO2
can be removed with acid. This suggests that valuable FTO-coated glass or TiO2 could be
recovered through a chemical recycling process. Rather than recycling the glass, the FTO-
coated glasses could be used in a remanufacturing process for new DSSCs [49]. The FTO
layer is resilient and cannot be removed by the described etching process. If the FTO layer
needs to be removed, e.g., for a possible recycling process, sulfuric acid or hydroiodic acid
is required [50,51].
3.2. ICP-OES
In Table 6. The results of the ICP-EOS are shown. In the right column, values of a
patent glass especially for photovoltaic usage are shown for comparison. Significant dif-
ferences are in the values of Al2O3. Sample t1A has significantly higher values than t1B.
The patent glass recommends even higher values and shows typical refining agents such
as sulfates, chloride, Sb2O3, As2O3 and SnO2 [52]. Aluminum oxide can increase the viscos-
ity of the glass as well as its chemical resistance [53]. CaO is also used in glass production
to increase viscosity and improve chemical resistance [54]. Therefore, it is possible that
either AlO3 or CaO is used in production due to price advantages of the materials.
Table 6. Chemical analysis by ICP-EOS, results in weight percentage.
t1A (%)
t1B (%)
Patent Glass [52] (%)
Materials 2021, 14, 6622 8 of 18
To reach highest efficiencies in photovoltaic applications, the Fe2O3 part in the glass
should be as small as possible because the light transmission through the glass is reduced
by iron. Fe2O3 absorbs photons of the UV spectrum, which reduces the efficiency of the
module [52]. For c-Si PV, even small amounts of Fe2O3, such as 1% in the front glass, re-
duce the efficiency by about 9.8% [55]. The glass thickness also influences the transmission
rate (thin glasses usually have higher transmission values) [56].
However, maximizing transmission and thus efficiency shortens the lifetime of the
entire c-Si PV system for conventional photovoltaic applications, which are usually lami-
nated with ethylene-vinyl acetate (EVA) foil. The UV light is responsible for degradation
of the foil and semiconductor material, which leads to efficiency losses or failure of the
module [57]. Therefore it is necessary to balance photovoltaic efficiency and degradation
by incorporating the right amount of Fe2O3 into the cover glass [56]. This is also important
for DSSCs due to aging processes inflicted by thermal stress and UV light [58]. For a gel
electrolyte DSSCs, thermal stress is less relevant because it exhibits higher thermal- and
photostability, compared to liquid electrolyte DSSCs [59]. An optimal cover glass for
DSSCs must be matched to the dye used and the specific absorption spectrum.
In the case of anthocyanin, the absorption spectrum has maxima at 465560 nm and
265275 nm [60]. Light with a wavelength of more than 560 nm would only heat up the
DSSCsthermal stress. Light in the ultraviolet range would lead to faster degradation of
the DSSC. Therefore, it is a balancing act between more efficiency and higher life expec-
tancy of the DSSCs. A cover glass that reflects or filters unnecessary wavelengths could
improve longevity without reducing the DSSCs efficiency. However, the absorption spec-
trum of anthocyanins can be modified by adjusting the pH of the dye [61]. The efficiency
increases at lower pH values. Junger et al. lowered the pH value from 2.3 to 1.1 and ob-
served that the efficiency could be doubled in this way [62]. In addition, copigmentation
with caffeine can improve the efficiency of anthocyanin-based DSSCs and the original pH
(2.3) can be maintained as the range of maximum efficiency is shifted from lower (1.1) to
higher (2.3) pH values [63]. Furthermore, a bathochromic shift of the anthocyanin spec-
trum can be observed when the dye is applied to TiO2. The absorption maximum of the
spectrum then shifts to higher wavelengths and lower light intensities [8]. This indicates
that the appropriate adjustment of cover glass and dye absorption spectrum has several
configuration options. In addition, different dyes are combined to improve the absorption
spectra and thus the energy conversion efficiency. For example, Bashar et al. combined
dyes from beetroot (80%) and spinach (20%) and significantly improved the energy con-
version efficiency from 0.56% (beetroot) and 0.49% (spinach) to 0.99% (combination of
dyes) [64]. This shows that, in addition to matching the cover glass to the absorption spec-
tra, co-sensitized DSSCs can be built from a variety of dyes to improve their power-con-
version efficiency.
3.3. Melting Experiment
Figure 3 shows the melts about 5, 20 and 50 min after the start of the melting process.
After 5 min, melts A and B already showed quite a lot of molten glass with seeds (air
inclusions < 1 mm) and bubbles (air inclusions > 1 mm). Melts C and D, on the other hand,
still exhibited significantly more unmelted batch and larger bubbles. Melt D, however,
was located at the front of the furnace and was therefore introduced into the furnace last
and removed first. The unmelted batch can be explained by the shortest melting time.
Materials 2021, 14, 6622 9 of 18
Figure 3. Glass melting after approx. 5, 20 and 50 min after the start of the melting process. From left to right A, B, C and
After 20 min, seeds and unmelted components could be determined. In direct com-
parison, melt D had the highest proportion of unmelted components and melt A the high-
est proportion of seeds.
Approximately 50 min after the start of the melting process no unmelted components
could be detected. Melt A and B showed optically coarser bubbles than melt C and D.
Figure 4 shows the melts after completion of the experiment and after the samples had
reached room temperature. All four melts show pinkish streaks at the bottom. Since the
control sample (melt A) also shows the pinkish streaks, they have to be caused by impu-
rities that do not originate from the DSSCs. Visually, the melts exhibited slightly different
colorations. Melt A showed a slightly bluish coloration, melt C showed a slightly greenish
coloration, and melt D showed a slightly pink coloration. The bluish coloration of melt A
might originate from higher Fe2O3 concentrations in the glass [54]. Melt B was very clear
and without any clearly discernible coloration. The colorations of melt C and D could
originate from contaminations such as dust, fingerprints and so on. This indicates that a
weathering process with simple water could increase the quality of the melt.
Materials 2021, 14, 6622 10 of 18
Figure 4. Melts after completion and cool down of the melting process. From left to right A, B, C and D.
3.4. Microscopic Examination of the Glass
For further examination of the glass quality, the samples were examined with a mi-
croscope. The results can be seen in Figure 5.
(Melt A)
(Melt B)
(Melt C)
(Melt D)
Figure 5. Microscopic images of the melts AD.
No inclusions (foreign bodies), such as small metal or ceramic pieces, were found in
any of the melts. The melts were visually similar. Melt C had the most streaks and the
most, predominantly small, seeds. Slightly fewer streaks were visible in melt D than in
Materials 2021, 14, 6622 11 of 18
melt C. In addition, the seeds present in the melt were somewhat larger. Melt A also had
slightly larger seeds and fewer detectable streaks than melt D. The most seeds were found
in melt B. The seeds were also slightly larger than in melt C. Melt B had the fewest dis-
cernible streaks. The melts with DSSC cullet are of similar quality compared to the refer-
ence sample. These results indicate that DSSCs, as described in this paper, are suitable for
a glass recycling process. Further investigations need to prove that the quality of DSSC
recycling glass is sufficient for container or flat glass. Gases that may have been generated
during the melting process were not monitored and should be investigated, especially if
plastic material contaminates the melt (PEO in this case). During the melting process, PEO
is thermally decomposed. This process takes place in a temperature range from 324 °C to
363 °C [65].
3.5. Industrial Scale-Up and Volume Estimation
The DSSC market is growing [7]. For this reason, an increasing amount of DSSC ma-
terials will require proper recycling processes in the future. The previous melting experi-
ment shows that at least non-toxic glass-based DSSCs have high potential for glass recy-
cling. To better understand the amount and composition of material that could enter re-
cycling facilities, it is estimated what a ton of DSSC material consists of. For recycling
plants, it is necessary to know the composition of the batch in order to properly adjust the
recycling processes.
Table 7 shows an estimate of how much material of what type could accrue in recy-
cling facilities in the future due to DSSC waste. The first column shows the material for
our non-toxic DSSCs. Column two shows an estimate from Parisi et al., who did a life
cycle assessment for DSSCs [41]. The glass thickness and the side lengths were determined
with a caliper gauge. The diameter of the glass plates is 7 cm², and the thickness is 0.1 cm.
The TiO2 layer is about 610 μm thick and is applied to about 6 cm². The FTO layer is very
thin and invisible; in this case, we estimated that the layer is about 10 nm thick and is
applied to the entire surface of the glass, i.e., 7 cm² each for the front and counter electrode.
Two drops of the commercial liquid electrolyte are used for a typical DSSC without PEO.
Each drop has a volume of about 2025 μL. Although the electrolyte evaporates over time
and not much of it would remain in a final recycling process, we listed it because residual
chemicals could still interfere with the recycling process. We have estimated a thickness
of 2 µm for the graphite layer. During the dyeing process, a monomolecular dye layer
adheres to the TiO2 layer. After the useful life of a DSSC, the organic dye is decomposed
by light or completely degraded in a final composting process before recycling. No gel
electrolyte or sealing was considered for the basic DSSCs.
Table 7. Material composition of one ton of DSSC.
Mass for 1 t of DSSCs, Basic Cells
Mass for 1 t of DSSCs, Parisi et al. [41]
FTO glass
977 kg
TCO glass
955 kg
7 kg
5 kg
15 kg
I /I3 liquid solu-
6 kg
1 kg
Platinum paste
1.5 kg
Dye, anthocyanin 1
Dye, Z907
0.06 kg
Silver paste
1 kg
31 kg
1 The front electrode is bathed in a solution of 2.5 g tea, 22.5 g of deionized water and 7.5 g of ethanol. Several DSSCs can
be dyed within one procedure. The biodegradable dye is not worth to be recycled in contrast to the ruthenium dyes [8].
Materials 2021, 14, 6622 12 of 18
The following material densities were used for the calculation of the material mass:
Glass: 2.5 g/cm³ [66],
TiO2 4.23 g/cm³ [67],
FTO/SnO2 6.99 g/cm³ [68] for thin films; the density of FTO is close to the density of
SnO2 [69],
Electrolyte: iodine/potassium iodide 1.12 g/cm³ [70],
Graphite 2.26 g/cm3 [71].
The volumes were multiplied by the densities and scaled up to one ton of material.
The results can be seen in Table 7.
Both estimates are similar to each other. According to our estimate, the electrolyte
volume is more than twice as large. More efficient production processes could probably
reduce this amount. In the estimate of Parisi et al. a toxic ruthenium dye is used. This
material hinders the recycling process and would poison the material cycle. Therefore,
such modules require an additional recycling step in which the toxic dye is separated from
the glass material [42]. DSSCs with organic dyes, on the other hand, could be used directly
in glass recycling after a natural weathering process.
TiO2 is commonly used for the construction of DSSCs and represents the best com-
promise between sustainability and high efficiency [72]. This material is quite safe and
abundant [73,74]. In France, however, TiO2 has been banned from foods because studies
suggest that TiO2 nanoparticles may cause health problems in rats [75]. Due to its white
color, TiO2 is often used in food as food additive E 171. TiO2 is already used in a variety
of applications, especially in the construction sector [76]. TiO2 is, moreover, already a com-
ponent of glass and could be used in glass recycling. However, recovery in a separation
process before recycling could be advantageous, e.g., reusing it directly for the production
of new DSSCs.
No platinum, silver or thermoplastic is used in our basic DSSCs. In the future, how-
ever, foils or films to prevent glass breakage or metal elements to improve conductivity
may be required. However, there are also metal-free solutions, such as carbon nanotubes,
to improve conductivity [15]. Thermoplastics can be used as sealants to prevent electrolyte
leakage, solvent evaporation and electrolyte corrosion [77]. As applied with the thermo-
plastic PEO to the DSSCs in this manuscript, melt C and D.
Since more and more photovoltaic modules already have to be recycled, there is ex-
perience of what problems arise in the process. This knowledge can be used to develop
more sustainable DSSCs. DSSCs have some components, such as the glass or a protective
film, that are also found in current c-Si PV modules [44].
An analysis of patent applications and the number of patents granted over the years
can provide some measure of the interest in the topic of photovoltaic cell recycling. Using
Web of Science resources and the Derwent Innovations Index database, where we
searched patent titles with the keywords solar cell recycling, we found 170 patents with
all categories of patent approval levels. For approved patents (at least category B), we
found 25 cases. Both search results are shown in the form of diagrams in Figures 6 and 7,
Materials 2021, 14, 6622 13 of 18
Figure 6. Distribution of the number of patents by country (all steps of a patent application process
including the first step A): China67, Japan44, Korea29, Taiwan11, Germany9, USA6,
India2, Great Britain1 and Switzerland1.
Figure 7. Distribution of the number of patents by country (the B step of a patent application process
meaning at least publication and preliminary approval): Korea17, Japan13, China6, Ger-
many4 and USA1.
The predominant technological recycling methods found in the descriptions of the
patents are as follows: removal of electrodes from solar cells, separation of anti-reflective
layers, recycling of electronic chips, reuse of electrically conductive glass substrates, re-
covery of atomic elements including silver and indium, removal of aluminum layers,
melting of tempered glass material, and recycling of crystalline silicon, among others.
Number of patents
All types of patent applications steps
China Japan Korea
Taiwan Germany USA
Number of patents
Patent applications with B category
China Japan Korea
Germany USA
Materials 2021, 14, 6622 14 of 18
Overall, it has not yet been possible to recover high-quality materials from the c-SI
PV module using a conventional glass recycling process [78]. Due to the shredding of the
modules, the materials are mixed and are difficult to separate by type.
In c-Si PV, EVA foil complicates the recycling process. One solution could be the use
of polyvinyl butyral (PVB) foil, which is also used in safety glass and for which mechanical
and chemical recycling processes exist [79,80]. There is also a patent that describes a
method of separating the laminated film from the glass [81]. This patent is not for c-Si PV
but for laminated safety glass. However, it could also be a model for recycling c-Si PV
modules using a similar process. An example of a photovoltaic application with PVB film
is Trosifol Solar [82]. They already use PVB film in their photovoltaic modules. For recy-
cling reasons, we recommend the use of PVB in future DSSC applications, if a film has to
be used at all.
The metal elements platinum and silver hinder the glass recycling process. So far, the
high-grade, low-iron glass from c-Si PV modules can only be used in a downcycling pro-
cess because during the recycling process the cullet is contaminated with iron parts [78].
In addition, there is the contamination by film residues and the silicon wafers. The
EOL-Cycle research project shows that an optimized recycling concept with more com-
plex and numerous cleaning and sorting steps enables the recovery of high-quality mate-
rials. However, it was not yet possible to achieve a sufficient degree of purity for the pro-
duction of flat glass [83]. Furthermore, there is the additional technical effort, which has a
negative impact on the economic efficiency of the process. Other problems with c-SI PV
recycling are the fluctuating composition of the PV modules and the use of materials that
are not pure, such as the use of different polymers [83].
A company from Japan is successfully using an automated system in which the glass
is separated from other components with a highly heated knife [84]. With such advanced
recycling processes, a downcycling process, at least for the glass, can be avoided.
By learning from the difficulties of recycling conventional PV technologies, DSSCs
can be made more suitable for future recycling. At least 70% of the environmental impact
of a product is determined in the design phase of the product. Therefore, it is reasonable
to invest effort into reducing the environmental impact of a product already in the design
phase [85]. By using recycled material or closing material loops for DSSCs, the energy
requirement for production can be reduced. The production of TCO glass in particular is
energy-intensive, and it would be beneficial to reuse the glass for constructing new DSSCs
[86]. Considering the global climate crisis and resource scarcity, sustainability should be
given the same importance as efficiency and stability in DSSC research [13,44]. In the de-
velopment of DSSC for the mass market, recycling must already be taken into account in
the design phase.
4. Conclusions
The experiment shows that the TiO2 could possibly be separated from the front elec-
trode by wet chemical processes. However, the FTO layer is very robust and cannot be
detached by the acid used.
Chemical analyses by ICP-OES revealed significant differences in the elements of the
two base glasses studied. In particular, significant differences were found for the elements
aluminum oxide and iron oxide.
The melting tests carried out showed slight differences in the melting behavior. In
the molten glass, the melts were visually quite similar but had slight color differences.
Melt B exhibited the highest brilliance and the lowest visually perceptible color impres-
sion, while melt D had a slightly pinkish tint and melt C a slightly greenish tint. All melts
exhibited visually perceptible color impression and showed a pinkish streak at the bottom
of the melt.
None of the samples showed inclusions in the glass melt, but visually perceptible
seeds could be detected. In general, all melts were similar. However, melt B had the fewest
Materials 2021, 14, 6622 15 of 18
seeds and visually perceptible streaks. In direct comparison, there were no distinctive dif-
ferences from the reference sample in either the melting behavior of the DSSC mixtures or
the glasses resulting from the melts. Further tests are necessary to investigate the suitabil-
ity of the resulting material for float and container glass production. For example, material
properties such as chemical resistance, transparency or viscosity must be evaluated.
Author Contributions: Conceptualization, writingoriginal draft preparation, investigation, data
curation, supervision, funding acquisition and project administration F.S.; methodology, visualiza-
tion F.S., J.L.S. and D.D.; performing of SEM-EDX, ICP-OES and melting experiment D.D.; valida-
tion, formal analysis review A.K.S., E.D., D.K., J.L.S., T.B. and E.S.-H. All authors have read and
agreed to the published version of the manuscript.
Funding: This research was funded by the State of NRW in scope of the project CirQuality OWL.
The APC was funded by the Open-Access Publication Fund of the University of Applied Sciences
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the
design of the study; in the collection, analyses, or interpretation of data; in the writing of the manu-
script; or in the decision to publish the results.
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... They mention that recycling could improve the environmental impact, but no practical experiments have been conducted so far [29]. In previous work, we investigated the recycling and remanufacturing potential of non-toxic DSSCs and found promising opportunities to use FTO-glass longer and integrate DSSCs in a glass recycling process [21,30,31]. ...
... If non-toxic DSSCs are used, they can potentially be used for conventional glass recycling [30]. When recycled cullet from DSSCs is used, indirect energy savings can be achieved because the extraction, mining, processing and transportation of raw materials are not required. ...
... Gap exploiter and access, selling or renting consumables with DSSC technology and taking it back for reuse or remanufacturing are some options. 5. DSSC can be used in glass recycling: At the end of the useful life, the non-toxic DSSC can be used in glass recycling [30]. ...
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In a world with growing demand for resources and a worsening climate crisis, it is imperative to research and put into practice more sustainable and regenerative products and processes. Especially in the energy sector, more sustainable systems that are recyclable, repairable and remanufacturable are needed. One promising technology is dye-sensitized solar cells (DSSCs). They can be manufactured with low energy input and can be made from non-toxic components. More than 70% of the environmental impact of a product is already determined in the design phase of a product, which is why it is essential to implement repair, remanufacturing and recycling concepts into the product design. In this publication, we explore appropriate design principles and business models that can be applied to DSSC technology. To realize this, we applied the concept of Circo Track, a method developed by the Technical University of Delft, to DSSCs and investigated which design concepts and business models are applicable. This method enables companies to transform a product that is disposed of after its useful life into one that can be used for longer and circulates in material cycles. The most important result is the description of a performance-based business model in which DSSCs are integrated into the customer’s building and green energy is provided as a service. During the operational phase, data is collected for product improvement and maintenance, and repair is executed when necessary. When the contract expires, it can be renewed, otherwise the modules are dismantled, reused, remanufactured or recycled.
To analyze the user's experience in glass recycling from a behavioral perspective, explore the interactive design method and feasibility of Fogg's behavioral model theory in the sustainable glass recycling system, and provide a theoretical basis for the development of sustainable glass recycling APP. By analyzing the current status of the glass recycling field, real cases, and the behavioral characteristics of users participating in glass recycling, combined with qualitative and quantitative research using the questionnaire interview method, the user's glass recycling experience journey map was drawn, and the pain points and difficulties of sustainable glass recycling were summarized. Explore the correlation between glass recycling and Fogg's behavior model, and propose an interactive design method and application strategy for sustainable glass recycling from three aspects: enhancing user motivation, improving user ability, and designing a trigger mechanism. Based on the Fogg model theory, the interactive design methods such as clear platform positioning, cultivating user achievements, redeeming points to encourage user participation, and timely and effective feedback are conducive to persuading users to participate in sustainable glass recycling actions, and have a certain impact on the design of sustainable glass recycling systems. Good guiding significance, and at the same time, it has reference value for improving the utilization rate of glass and prolonging its life cycle.Keywordsglass recyclingbehavioral designFogg modelsustainable
Harnessing energy from the surrounding light using indoor photovoltaics has gained momentum to address the carbon footprint resulting from used and dead batteries. Dye-sensitized solar cells (DSCs) has emerged as...
Solar energy has an important role for increasing renewable energy use and circularity options in the sector are increasing. This study analyses the advances in the scope of the Sustainable Development Goals that aim to create a more equitable and peaceful world and a more livable environment. Studies that are focused on life cycle perspectives, opportunities for end-of-life management, and multiple goals, including climate action as well as responsible consumption and production are compared. This is used to understand synergies between the circular economy and solar photovoltaic technologies in Türkiye. A need analysis survey is conducted with the participation of academic institutions and research centers, producers, and other stakeholders who operate in the solar photovoltaic sector in Türkiye. The results are analyzed across stakeholder categories and used to derive policy recommendations based on the top drivers, barriers, and enablers to increase circularity in the sector. The expected impacts on environmental, economic and social aspects are also questioned to obtain perspectives on possible pathways. For the first time, the realization of sustainable solar photovoltaic waste management in the context of the circular economy is discussed by stakeholders in Türkiye to establish consensus, increase collaboration, and support planning of future opportunities
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The deployment of photovoltaic technologies is forecast to increase substantially in the near to mid future to meet society's energy demand in a sustainable way. Dye-sensitized solar cells (DSSCs) in...
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: Porous organic molecular materials represent an emergent field of research in Chemistry and Materials Science due to their unique combination of properties. To enhance their performance and expand the number of applications, the incorporation of hierarchical porosity is required, as exclusive microporosity entails several limitations. However, the integration of macropores in porous organic molecular materials is still an outstanding challenge. Herein, we report the first example of a hydrogen‐bonded organic framework ( MM‐TPY ) with hierarchical skeletal morphology, containing stable micro‐ and macroporosity. The crystal size, from micro to centimetre scale, can be controlled in a single step without using additives or templates. The mechanism of assembly during the crystal formation is compatible with a skeletal crystal growt h. As proof of concept, we employed the hierarchical porosity as a platform for the dual, sequential and selective co‐recognition of molecular species and microparticles.
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Resources are becoming more expensive and less accessible, for instance construction wood or semiconductors. In addition, climate change requires the conversion of the energy system to 100% renewable energy. Therefore, we need resources to prevent the climate crisis from worsening, but at the same time, we are suffering from a worsening resource crisis. State-of-the-art technologies, such as silicon-based photovoltaic or wind power plants, are harnessing renewable energy but causing problems and resource losses at the end of their useful life. This alarming situation must be addressed with renewable energy technologies that can be used longer, repaired and remanufactured, and properly recycled at the end of their useful life. An emerging technology that can complement the established systems is dye-sensitized solar cells (DSSCs). Their production is less energy intensive and they can be manufactured without toxic materials. In line with the concept of the circular economy, the service life of all products must be improved in order to reduce resource consumption. Therefore, we investigated the potential for remanufacturing DSSCs by taking apart old DSSCs, cleaning the components, and building new DSSCs from the remanufactured components. The remanufactured DSSCs have the same or higher efficiencies and can be remanufactured multiple times.
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The electrolyte for dye-sensitized solar cells (DSSCs) is subject of constant innovation, as the problems of leakage and drying greatly reduce the long-term stability of a device. One possible way to solve these problems is the use of gel polymer electrolytes (GPEs) with a gelling structure, which offer different advantages based on the used polymers. Here, potential GPE systems based on dimethyl sulfoxide (DMSO) as solvent for low-cost, non-toxic and environmentally friendly DSSCs were investigated comparatively. In order to observe a potential improvement in long-term stability, the efficiencies of DSSCs with different GPEs, consisting of polyacrylonitrile (PAN), acrylonitrilebutadiene-styrene (ABS), polyvinyl alcohol (PVA) and poly (vinylidene fluoride) (PVDF) and their blends with poly (ethylene oxide) (PEO), were investigated over a period of 120 days. The results indicate that blending the polymers with PEO achieves better results concerning long-term stability and overall efficiency. Especially the mixtures with PAN and PVDF show only slight signs of deterioration after 120 days of measurement.
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In times of climate change and dwindling fossil resources, the need for sustainable renewable energy technologies gains importance, increasingly fast. However, the state of the art technologies are energy intensive in their production, like monocrystalline photovoltaic, or even consist of not recyclable composite material, in the case of wind turbine blades. Despite a lack in efficiency and stability, dye sensitized solar cells (DSSC) have a high potential to supplement the state of the art green energy technology in future. With low production costs and no necessity for toxic compounds DSSCs are a potential product, which could circulate in the loops of a circular economy. Therefore, with this paper, we provide the status of research on DSSC recycling and an outlook on how recycling streams could be realized in the future for glass-based DSSCs without toxic components. The overview includes work on using recycled material to build DSSCs and extending the life of a DSSC, e.g., through rehydration. We also illustrate the state of sustainability research for DSSCs using the VOSviewer tool. To date, the term sustainability appears in 35 of 24,441 publications on DSSCs. In view of the global challenges, sustainability should be researched more seriously because it is as important as the efficiency and stability of DSSCs.
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Organic–inorganic perovskite solar cells (PSCs) have recently emerged as a potential candidate for large-scale and low-cost photovoltaic devices. However, the technology is still susceptible to degradation issues and toxicity concerns due to the presence of lead (Pb). Therefore, investigation on ideal methods to deal with PSC wastes once the device attains its end-of-life is crucial and to recycle the components within the cell is the most cost effective and energy effective method by far. This paper reported on a layer-by-layer extraction approach to recycle the fluorine-doped tin oxide (FTO) coated glass substrate which is the most expensive component in the device architecture of mesoporous planar PSC. By adapting the sequential removal of each layer, chemical properties of individual components, including spiro-OMeTAD and gold can be preserved, enabling the material to be easily reused. It also ensured that the toxic Pb component could be isolated without contaminating other materials. The removal of all individual layers allows the retrieval of FTO conductive glass which can be used in various applications that are not only restricted to photovoltaics. Comparison of electrical, morphological and physical properties of recycled FTO glasses to commercial ones revealed minimal variations. This confirmed that the recycling approach was useful in retrieving the substrate without affecting its physicochemical properties.
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Laminated glass is ever more frequently used nowadays. This applies to the automobile industry and the construction industry. In cars, this refers mostly to the front and rear windows, whereas in construction, technical safety glass is used for railings and window glass. The task of this type of glass is to provide sufficient resistance against mechanical impact and unpleasant weather conditions. At the same time, if it is damaged, it has to break into the smallest possible pieces, or, wherever possible, the glass should remain intact on the interlayer film to prevent shards from injuring people and animals in the immediate vicinity. The paper deals with the recycling of laminated glass, especially with the effective separation of glass (in the form of cullet) from the polyvinyl butyral (PVB) interlayer film. The experimental research is focused on the mechanical separation of glass from the interlayer film by vibration, and also on the chemical cleaning of PVB film in order to allow subsequent recycling of both materials. The results quantify the efficiency of mechanical separation in the form of weight loss of the sample of laminated glass and define the particle size distribution of glass cullet, which is an important parameter in the possibility of glass recycling. The research leads to a methodology proposal for the separation of glass and PVB film and the design of equipment for this method.
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Alongside efficiency, long-term stability of dye-sensitized solar cells (DSSCs) is a key factor regarding their commercialization. One suitable and cost-effective method to increase the long-term stability is to prevent leakage and evaporation of the electrolyte by gelling it with polymers such as poly(ethylene oxide) (PEO) and gaining a gel polymer electrolyte (GPE). In this study, a GPE based on PEO and glycerol is investigated for the first time as electrolyte for environmentally friendly DSSCs with natural dyes. To evaluate the novel glycerol/PEO GPE, the ionic conductivity and resulting efficiency progressions of DSSCs were measured for 75 days. Different molecular weights (MWs) of PEO and blending with poly(vinylidene fluoride) (PVDF) had negligible impact on efficiencies. 17 wt% PEO was found to be more suitable than lower concentrations and resulted in a relatively high efficiency over 75 days. A glycerol electrolyte without PEO had higher ionic conductivity and achieved higher efficiencies as well but leaked from the unsealed DSSCs. In addition, the reproducibility was examined especially, which appeared to be reduced by considerable differences between identical DSSCs and between measurements of the same DSSC at different times. This emphasizes the relevance of studying multiple DSSC per sample to ensure reliable results.
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To overcome the long-term stability problems of dye-sensitized solar cells (DSSC) due to solvent evaporation and leakage, gelling the electrolyte with polymers is an appropriate option. Especially for future applications of textile-based DSSCs, which require cost-effective and environmentally friendly materials, such an improvement of the electrolyte is necessary. Therefore, the temporal progressions of efficiencies and fill factors of non-toxic glass-based DSSCs resulting from different gel electrolytes with poly(ethylene oxide) (PEO) are investigated over 52 days comparatively. Dimethyl sulfoxide (DMSO) proved to be a suitable non-toxic solvent for the proposed gel electrolyte without ionic liquids. A PEO concentration of 17.4 wt% resulted in an optimal compromise with a relatively high efficiency over the entire period. Lower concentrations resulted in higher efficiencies during the first days but in a poorer long-term stability, whereas a higher PEO concentration resulted in an overall lower efficiency. Solvent remaining in the gel electrolyte during application was found advantageous compared to previous solvent evaporation. In contrast to a commercial liquid electrolyte, the long-term stability regarding the efficiency was improved successfully with a similar fill factor and thus equal quality.
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For the solar energy industry to increase its competitiveness, there is a global drive to lower the cost of solar‐generated electricity. Photovoltaic (PV) module assembly is material‐demanding, and the cover glass constitutes a significant proportion of the cost. Currently, 3‐mm‐thick glass is the predominant cover material for PV modules, accounting for 10%–25% of the total cost. Here, we review the state‐of‐the‐art of cover glasses for PV modules and present our recent results for improvement of the glass. These improvements were demonstrated in terms of mechanical, chemical and optical properties by optimizing the glass composition, including addition of novel dopants, to produce cover glasses that can provide (i) enhanced UV protection of polymeric PV module components, potentially increasing module service lifetimes; (ii) re‐emission of a proportion of the absorbed UV photon energy as visible photons capable of being absorbed by the solar cells, thereby increasing PV module efficiencies and (iii) successful laboratory‐scale demonstration of proof of concept, with increases of 1%–6% in Isc and 1%–8% in Ipm. Improvements in both chemical and crack resistance of the cover glass were also achieved through modest chemical reformulation, highlighting what may be achievable within existing manufacturing technology constraints.
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Dye-sensitized solar cells (DSSCs), as emerging photovoltaic technology, have been thoroughly and extensively investigated in the last three decades. Since their first appearance in 1991, DSSCs have gained increasing attention and have been classified as feasible alternatives to conventional photovoltaic devices due to their numerous advantages, such as cheap and simple preparation methods, the possibility of being integrated in buildings and astonishing performances under indoor and diffuse illumination conditions. Photoconversion efficiencies of up to 14% and 8% have been obtained for lab-scale devices and modules, respectively. Albeit the efforts made, these values seem arduous to be outdone, at least under simulated solar radiation. Nevertheless, recent lab-scale systems have demonstrated photoconversion efficiencies of up to 33% under indoor illumination (i.e. 1000 lux) leading to an actual Renaissance (or Revival) of these devices. It is worth mentioning that scientists in this field are developing innovative materials aiming at long-term and efficient devices, being the concept of sustainability often set apart. However, in light of effective commercialization of this technology, stability, efficiency and sustainability should be considered as the essential keywords. Nowadays, DSSCs are finding a “new way back” towards sustainability and rather a huge number of reports have focused on the preparation of green and cost-effective materials to replace the standard ones. In this scenario, the present review aims to give an overview of the most adopted strategies to enhance the sustainability of materials in classical DSSC components (e.g. sensitizer, redox couple, electrolyte and counter-electrode), including smart synthesis and deposition procedures, which currently represent utmost important topics in the scientific community.
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Zusammenfassung Farbstoffsolarzellen bieten eine interessante Alternative zu herkömmlichen Solarzellen. Ihre Herstellung benötigt keine Reinräume und viel weniger Energie als etwa Siliziumsolarzellen. Allerdings sind ihre aktuellen Wirkungsgrade besonders bei Nutzung preiswerter, ungiftiger Materialien sehr niedrig. Sie genügen noch nicht, um einen essentiellen Beitrag zur Energiewende zu leisten. Farbstoffsolarzellen können aber bereits jetzt für Stand‐alone‐Lösungen, in textiler Architektur oder auf anderen großen Flächen eingesetzt werden. Dies kann sinnvoller und umweltschonender sein als der Einsatz herkömmlicher siliziumbasierte Zellen.