- Introduction
As per available records, about 570,000 premature deaths in India were due to air pollution caused by various conventional energy sources. Also, an additional 12,000 were killed caused by exposure to global warming. Inhaling of these pollutants causes serious health problems for human beings as well as for animals. Power generation from steam plants releases CO2, NO2, and sulphur as by-products in the environment and causes a serious imbalance in our ecosystem. Still, there are plenty suffering from various diseases due to inhalation of air from the polluted atmosphere. So, we need to switch towards a cleaner source of energy. The best available option is solar energy. Sunlight is an unlimited source of energy. By harvesting this solar energy into electricity efficiently, the problem of shortage of electricity can be solved particularly in remote and backward areas. There are several photovoltaic cells from the first and second generations that have been used to provide renewable, abundant, and silent energy on earth. Several photovoltaic cells have been used to provide renewable energy for humanity on earth. Although these cells are being used at a commercial scale but still, they suffer from few drawbacks:
(1) They are costly as compared to conventional sources.
(2) They are bulky and require large land space for installation.
(3) These cells also suffer from pollution-related drawbacks as they also release certain toxic chemicals in the atmosphere during the energy production process.
Dye-sensitized solar cells (DSSCs) are arranged in a group of thin-film solar cells which are under research due to their low cost, simple preparation methodology, low toxicity, and ease of production. Still, there is a lot of scope for the replacement of current DSSC materials due to their high cost, less abundance, and long-term stability. So, we still need to move towards a cleaner source of energy for the survival of humans. DSSC seems to be the best option for energy production that typically considers all the drawbacks of the above-mentioned energy sources. The presence of a natural dye and flexibility along with cleaner energy is the main characteristic features of the cell.
- Physical and Financial benefits
For this DSSC cell, different dyes having content of anthocyanin pigment as in natural fruits, vegetable leaves, vegetables, and flowers can be extracted. Based on the observations and analysis from the highly sophisticated instruments, comparative statistics can be prepared on the absorption of the photon in the visible spectrum corresponding to the wavelength. The more the absorption of the photon, the greater is the electrons injection to the semiconducting material (e.g., TiO2) from the dye. The best natural dye so far identified is from pomegranate juice. The carbonyl and hydroxyl group present in the anthocyanin makes it better to attach to TiO2 nanoparticles. In this blog, some important properties of natural polymer electrolytes are listed for investigation.
- Physical Benefits: No Pollution, less space required, Constant efficiency for 20 years and Flexibility
- Financial Benefit: Cheap source, Government provides a subsidy to the end-users of green energy
Based on the development of solar cells; it has been divided into 3 generations. The first-generation solar cells were made of monocrystalline and Polycrystalline silicon. In the second-generation cells, thin films were used that provided a good aesthetic appearance to the solar cells. Third-generation solar cells are based on Nanoparticles, Polymers, and Dye Sensitized solar cells (DSSC). Although the efficiency of DSSC is low, it is low in cost and very easy to manufacture. Also, raw materials for the manufacturing of these cells are easily available these cells are available in different colours. Table no 1 compares the properties of DSSC with existing solar cell technology. In table 1, it is easily recognizable that by working on the efficiency factor, DSSC exhibits better results as compared to other solar cells.
Table 1: Comparison between DSSC and other semiconductor based solar cells
| Parameter | Semiconductor Solar Cell | DSSC |
| Transparency | Opaque | Transparent |
| Power Generation Cost | High | Low |
| Power Generation Efficiency | High | Normal |
| Colour | Limited | Various |
- Materials and Methods
Various natural composite dyes are reported to exist and their study on solar spectrum absorption can be analysed in the laboratories. Polymer electrolyte is reported to have maximum conductivity i.e., 10-3 S/cm based on natural (Chitin/Agar Agar/Tamarind/Arrowroot) polymers. But for further improving the characteristics, they can be synthesized also. Maximum absorbing dye and its compatibility with natural polymer electrolyte is also an important factor to explore for getting maximum efficiency of DSSC cell. Further enhancement of conductivity can be achieved by incorporating various nanoparticles (CNT, TiO2, ZnO, CDS) in natural polymer electrolytes. Based on existing literature review and research papers, the following techniques can be employed to start with environment friendly DSSC cell, as mentioned below:
Ø Fabrication of Natural Dye:
Combination of various dyes like anthocyanin, Heena, Chlorophyll, Pomegranate, raspberry, beetroot, etc to synthesize a composite dye having maximum absorption of the solar spectrum.
Ø Fabrication of natural polymer electrolyte:
Arrowroot/chitin/Tamarind will be treated with various salts (like NaI, KI, LiI, NH4I) to form a polymer electrolyte. Conductivity can be further increased by using nanoparticles like ZnO, TiO2, CdS, CNT.
Ø Assembling various components to form a complete DSSC:
The optimum concentration of dye, PE along with electrode and counter electrode will be assembled to fabricate DSSC.
Ø I-V characteristics of fabricated cell:
I-V curve to study the efficiency and fill factor of the fabricated DSSC.
The major drawback lies in its light-harvesting efficiency. These cells are not able to absorb the complete solar spectrum. In the case of DSSC, it can be made to utilize the maximum portion of solar spectra and convert it into a useful form of energy.
- Structure and Working of DSSC
As per the research article Sharma K et al. (Dye-Sensitized Solar Cells: Fundamentals and Current Status), Dye Sensitized solar cells convert any visible light into electrical energy. This cell has a working principle that is closely likened to artificial photosynthesis due to how it absorbs light energy. As a disruptive technology, this cell is capable of producing electricity in all kinds of light conditions that are present indoors and outdoors. It can convert both artificial and natural light into electricity. The working principle of DSSC involves four basic steps: light absorption, electron injection, transportation of carrier, and collection of current. In the first step, the incident light (photon) is absorbed by a photosensitizer, and thus, due to the photon absorption, electrons get promoted from the ground state to the excited state.
Figure 1. Schematic Diagram of DSSC assembly
Secondly, the excited electrons with a lifetime of nanosecond range are injected into the conduction band of the nano porous TiO2 electrode which lies below the excited state of the dye, where the TiO2 absorbs a small fraction of the solar photons from the UV region. In the third step, these injected electrons are transported between TiO2 nanoparticles and diffuse towards the back contact (transparent conducting oxide [TCO]). Through the external circuit, electrons reach the counter electrode. In the final step, dye regeneration or the regeneration of the ground state of the dye takes place due to the acceptance of electrons.
- Conclusion
Existing solar cells suffer from emitting toxic gases. DSSC solar cell has low cost and is eco-friendly, but the efficiency is still not so high to go for commercialization at this stage. This problem can be overcome by developing natural composite DSSC cells having sustainable functioning with higher efficiency. In terms of their commercial application, a DSSC needs to be sustainable for more than 25 years. A lot of research is undergoing in this field and lots of government funding are available for innovative ideas that can be achieved with all the possible objectives discussed in this blog.
Dr. Sandeep Dhariwal
Associate Professor
Alliance College of Engineering and Design