METHOD FOR SYNTHESIZING CARBON DOTS FROM SYZYGIUM CUMINI FOR ENHANCED PERFORMANCE OF DYE SENSITIZED

Abstract

The increasing global energy demand, driven by population growth and technological advancements, heavily relies on fossil fuels, which are depleting and contributing to health issues and environmental concerns, such as respiratory diseases and global warming. Transitioning to renewable energy sources, particularly solar energy, is .essential for sustainable energy generation. Dye-sensitized solar cells (DSSCs) have garnered interest due to their ease of fabrication, ceo-friendliness, and suitability for indoor applications. The efficiency of DSSCs is largely determined by the performance of their photoanodes, making the enhancement of TiO,-based photoanodes a key research focus. This invention presents a green synthesis method for producing carbon dots (COs) from Syzygium cumini seeds through acidic oxidation, aimed at utilizing these COs as a modifying agent for TiO,based DSSCs. Comparative studies of DSSCs with unmodified and CO-modified photoanodes indicate that the device with COs demonstrates improved performance. The unmodified device achieved a shortcircuit current density (Jsc) of 14.03 mNcm2 , an open-circuit voltage (Voc) of0.79 V, a fill factor (FF) of51.70%, and a photoconversion efficiency (PCE) of5.73%. Whereas, the modified device exhibited a Jsc of 18.59 mA/cm2 , a Voc of0.78 V, an FF of47.58%, and a PCE of6.90%. This approach offers a cost-effective and environmentally friendly strategy to enhance the performance ofDSSCs

Specification

FIELD OF THE INVENTION
[0001] The present innovation focuses on enhancing the efficiency of dye-sensitized solar cells
(DSSCs) by modifying the photoanode with carbon dots (COs) synthesized from Syzygium cumini
seeds. This approach aims to improve the photovoltaic performance of the cells, potentially leading
to better energy conversion efficiency.
BACKGROUND OF THE INVENTION
[0002) The global demand for energy has risen drastically over the years due to population growth
and technological development. To meet this vast demand, fossil fuels remain the dominant
resource, although they are facing rapid depletion. Moreover, the extensive use of fossil fuels
results in various health hazards, including respiratory diseases and lung cancer, due to pollution.
Additionally, their use has serious environmental consequences, such as global warming caused
by increased greenhouse gas emissions. The most effective way to meet global energy demands
while safeguarding health and the environment is to shift toward renewable energy sources.
Renewable energy sources, such as solar energy, wind energy, geothermal energy, and hydropower
have recently garnered significant interest as clean energy solutions. Among these, solar energy
stands out due to its abundance and potential for sustainable energy generation.
[0003] Various solar energy technologies have emerged over time, including DSSCs, which
belong to the third generation of solar cells. DSSCs are advantageous due to their ease of
fabrication, environmental friendliness, and potential for indoor applications where limited
sunlight is available. DSSCs typically consist of a photoanode, dye, electrolyte, and counter
electrode. The photoanode plays a crucial role in determining the overall performance of the
DSSC. As such, numerous studies have been conducted to improve the performance of
photoanodes. One notable approach is the modification of TiOz-based photoanodes to enhance
properties that can ultimately boost DSSC efficiency.
[0004] Carbon nanomaterials are known for their unique and remarkable properties, making them
suitable for a wide range of applications. CDs are carbon nanoparticles less than I 0 nm in size,
possessing exceptional physicochemical properties, including distinct optical characteristics.
Modifying DSSC photoanodes with CDs can improve the performance of the device, primarily by
extending light absorption and enhancing charge transfer properties. Additionally, the green
synthesis of CDs offers an environmentally friendly and cost-effective production method.
[0005] Syzygium cumini, commonly known as black plum or jambolan, is a medicinal plant widely
found in tropical regions. The seeds of Syzygium cumini and their derivatives have been employed
in various medical and energy storage applications. The present invention aims to develop CDs
from Syzygium cumini seeds via acidic oxidation and utilize them as a photoanode-modifying agent
for Ti02-based DSSCs. DSSCs with both unmodified and CD-modified photoanodes were
fabricated, and their photovoltaic performance was compared. Results demonstrated that Syzygium
cumini seed-derived CDs are effective photoanode modifiers, leading to improved current density
and enhanced efficiency. This method represents an efficient strategy for enhancing DSSC
performance through a cost-effective and environmentally friendly approach.
[0006] US9919927B2 details a method for the synthesis of graphene quantum dots from coal and
coke by heating them in the presence of an oxidant. US20 120160307 A I explains the method of
fabricating a DSSC which is comprised of a dye-sensitized Ti02 layer as the photoanode, a
platinum layer as counter electrode, and an electrolyte sandwiched between the photoanode and
the counter electrode. US20080264485A I describes a method for the manufacturing of DSSC in
which the photoanode is modified with a fluorescent material which resulted in an enhancement
of the photo conversion efficiency facilitated by the optical properties of the fluorescent material
used. KRI00773147BI also details the preparation method ofDSSC in which the photoanode is
composed of Ti02 and a fluorescent material. The power conversion efficiency of the device was
improved through the light emitting characteristics of the fluorescent material in the visible region.
US20100269270Al describes the fabrication DSSC in which a nanocomposite composed ofTi02
and a functionalized carbon nanomaterial is utilized as the photoanode material. The incorporation
of the carbon nanomaterials in to the Ti02 enhanced the dye adsorption which resulted in an
elevated photoconversion efficiency of DSSC.
[0007] This invention introduces a simple and low-cost method for synthesizing COs from the
seeds of Syzygium cumini, which are used to modify the TiO, photoanode in OSSCs to enhance
power conversion efficiency. The synthesis process begins with collecting and thoroughly cleaning
Syzygium cumini seeds using deionized water, followed by air-drying at room temperature. The
dried seeds are then crushed into powder and subjected to heat treatment at 200°C for 2 hours.
After cooling to room temperature, the material is treated with 2M nitric acid. The mixture is
stirred at 60°C overnight to promote oxidation and extract the COs. Finally, the solution is
centrifuged and washed multiple times with distilled water to remove residual acids and impurities,
yielding purified COs.
[0008] The COs derived from Syzygium cumini were mixed with TiO, to create a modified
photoanode. The photovoltaic performance of both the unmodified and modified photoanodes was
evaluated, and the incorporation of COs was found to enhance the overall OSSC perfonnance,
leading to improved power conversion efficiency.
[0009) In an additional embodiment, the modification of the Ti02 photoanode with Syzygium
~ cumini-derived COs is explained. Another embodiment discusses the fabrication process of the
~ OSSC.
Q)
[0010) For greater clarity regarding the present invention, a detailed description and
comprehensive illustrations are provided. These figures depict a typical embodiment of the
invention, serving as a foundational example that can be further developed to explore potential
extensions and variations.
[0011] We claim,
I. A method for synthesizing carbon dots from Syzygium cumini seeds involves drying and
crushing the seeds into powder, heating at 200°C for 2 hours, treating with 2M nitric acid at 60°C
overnight, then centrifuging and washing to obtain the carbon dots.
2. A method for fabricating a dye-sensitized solar cell photoanode comprised of Ti02 modified
with Syzygium cumini-derived carbon dots involves mixing the carbon dots with Ti02 paste coating it onto a cleaned FTO substrate via the doctor blade technique, annealing at 500°C for I
hour, and performing a TiCI4 treatment followed by sintering at 500°C for 30 minutes.
3. The carbon dots derived from Syzygium cumini, as claimed in claim I, wherein the particles are
quasi spherical in shape with size less than I 0 nm.
4. The carbon dots derived from Syzygium cumini, as described in claim I, wherein carbon dots
are characterized by the presence of various functional groups.
5. The carbon dots derived from Syzygium cumini, as described in claim I, wherein carbon dots
are composed of carbon, oxygen and nitrogen.
6. The photoanode of the dye-sensitized solar cells modified with carbon dots derived from
Syzygium cumini as claimed in claim 2, wherein the carbon dots modify the band gap of the Ti02
from 3.4 eV to 3.2 eV and improved the light absorption properties.
7. The photoanode of the dye-sensitized solar cells modified with carbon dots derived from
Syzygium cumini as claimed in claim 2, wherein the charge transfer resistance of the photoanode
reduce from 57.5 to 32.3 by the addition of carbon dots.
8. The photoanode of the dye-sensitized solar cells modified with carbon dots derived from
Syzygium cumini as claimed in claim 2, wherein the addition of carbon dots enhances the
photovoltaic performance of the DSSC, resulting in a photo conversion efficiency greater than
6.0%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] To provide a clearer understanding of the current invention, a comprehensive explanation
of the disclosure, along with detailed illustrations, is presented. The research focuses on
synthesizing CDs from Syzygium cumini seeds and utilizing them as a photoanode modification
agent in DSSCs to achieve improved efficiency. The invention will be explained in detail, with
accompanying diagrams aiding in the understanding of the novel aspects outlined in this work.
[0013] Figure I illustrates a flow chart of the procedure for synthesizing CDs from the seeds of
Syzygium cumini This invention emphasizes the significance of using CDs derived from Syzygium cumini
seeds to improve the performance parameters of DSSCs by incorporating them as a photoanode
modification material. Key attributes of these CDs include their widespread availability,
affordability, non-toxic properties, and the cost-efficient synthesis process. Acting as a coactivation
agent with Ti02, these CDs play a crucial role in boosting the current density and overall
photoconversion efficiency of the DSSC.
(0021] A simple procedure was employed to synthesize CDs from Syzygium cumini seeds. The
precursor seeds were collected, thoroughly cleaned with distilled water, and air-dried. Afterward,
the seeds were crushed and heated at 200°C for 2 hours. Once cooled to room temperature, the
material was treated with 2M nitric acid and stirred overnight at 60°C. The resulting product was
then centrifuged and repeatedly washed with distilled water to isolate the CDs.
[0022] To prepare the modified photoanode, Ti02 was first ground in ethanol, and ethyl cellulose Figure 7a displays the J-V characteristics of OSSC devices fabricated with both modified
and unmodified photoanodes. The OSSC device modified with COs derived from Syzygium cumini
seeds demonstrated enhanced output parameters compared to the unmodified device. The graph
reveals a notable increase in current density. Specifically, the unmodified device achieved a shortcircuit
current density (Jsc) of 14.03 mA/cm2
, an open-circuit voltage (Voc) of0.79 V, a fill factor
(FF) of 51.70%, and a photoconversion efficiency (PCE) of5.73%. In contrast, the device with the
modified photoanode exhibited improved output parameters, with Jsc of 18.59 mA/cm2
, Voc of
0.78 V, FF of47.58%, and PCE of6.90%. Figure 7b compares the Nyquist plots for both modified
and unmodified OSSC devices. The series resistance for both devices is nearly the same. However,
the charge transfer resistance between the photoanode and the dye is significantly lower in the
OSSC with the photoanode modified with the synthesized COs. Specifically, the charge transfer
resistance for the unmodified device is measured at 57.57 n, while the modified device shows a
reduced resistance of32.3 7 n.
(0032( Although specific language has been employed to clarify the disclosure, any limitations
resulting from it are unintentional. It should be evident to those skilled in the art that various
modifications can be made to the method to effectively implement the inventive concept presented
here.
[0033] The figures and descriptions provided illustrate examples of various embodiments. Those
skilled in the art will recognize that one or more of the described elements can be combined into a
single functional unit, or conversely, certain elements may be separated into distinct functional
components. Additionally, elements from one embodiment may be integrated into another. The
actions depicted in any flow diagram do not need to be executed in the specific order presented,
nor is it necessary for all actions to be performed. Furthermore, actions that are independent of one
another may occur in parallel. Therefore, it is understood that the appended claims are intended to
encompass all such modifications and alterations that align with the true spirit of the invention

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