The revolution for efficient and sustainable conversion of solar energy is entirely driven by material. Quantum dots, nanometer-scale semiconductor particles, are the talk of the sector when it comes to propelling materials science to push the level’s boundaries and break the efficiency records of super-efficient quantum dot solar cells. This article describes quantum dots in more detail, explains the aspects of their influence on solar energy conversion, and outlines why they seed grounds for high performances that break the efficacy records of the current solar cells.
Understanding Solar Energy Conversion
Solar energy conversion implies the process of photons being converted into electricity. In general, a critical role herein should be played by solar cells, also known as photovoltaic cells. The classical photon materials based on crystalline silicon manifested low performance and eventually offered many drawbacks, such as low performance or high installation cost. The very essence of maximising the performance to the quantum dot level is quantified by their unique features, which enable the use of a more significant fraction of energy from the photons.Â
Properties of Quantum Dots Solar Cells
Distinctive properties of quantum dots (QDs) embody nanometer-size semiconductor nanoparticles, with their properties being directly reliant on these three features: size, shape, and the elements included.
What prompted scientists to believe that quantum dots could be the potential solution for improving solar energy conversion?Â
Tunable Bandgap
Quantum dots allow engineers to develop dots with a tunable bandgap. This characteristic enables quantum dots to absorb a broad spectrum of sunlight, including visible and infrared light. This feature is essential because better light absorption leads to more effective conversion.
Solution Processability
Quantum dots are solution-processable, meaning they can be easily applied to thin films in solar cell applications. Although this feature does not impact the quantum dots themselves, it influences the solar cell manufacturing process, making it less complex and cheaper.
High Absorption Cross-Section
When quantum dots are struck by photons of incoming light, they create electron-hole pairs in a process called high absorbance cross-section. This process signifies how well quantum dots generate charge when illuminated.
Working of Quantum Dot Sensitized Solar Cells (QDSSCs)
The application of quantum dots in solar conversion is considered quantum dot-sensitised solar cells. The quantum dots are set within this type of cell to optimise light absorption and enhance electron-hole pair production.
In brief, QDSSC works by,
- Light Absorption: The solar cell is sensitised by quantum dots, which, when irradiated by sunrays, absorb broad-spectrum photons and convert them to electron-hole pairs.
- Electron Injection: The electrons are ejected toward the electron transport layer while the holes are deposited on a hole transport layer. The flow of these charges becomes a ready source of electricity.
- Electron Collection: The electrons drift through an external circuit and produce electricity. Quantum dots can help push the efficiency limits of solar cells.
Some of the ways in which quantum dots boost the performance of solar cells are explained below.
How Can Quantum Dots Be Used to Improve Solar Cells?
The solar power industry faces a conundrum. While existing-generation solar cell technologies have seen their efficiencies driven close to practical limits by decades of research & development, significant new gains in solar photovoltaic efficiencies will likely have to come from new technologies like quantum dot technology.
Efficiency of Third-Generation Quantum Dots:
Prospecting for what is often termed a third generation of solar-cell technologies, which will follow silicon and thin-film solar cells currently in the maturity stage of the technology adoption lifecycle, quantum dots, tiny spheres of semiconductor material, with diameters measuring about 2-10 billionths of a meter.
Quantum dots also have the potential to improve sunlight-to-energy conversion efficiency by many orders of magnitude, doubling it in some cases. This capability is due to the ability to create more than one bound electron-and-hole pair per incoming photon—that is, more than one exciton.
Today’s solar cells generate only one exciton. However, the “multiple exciton generation,” or MEG, effect of quantum dots indeed pries out more energy from each photon. Further, by changing the size of quantum dots, one can virtually tune them to respond to different light wavelengths. As quantum dots get smaller, the light they absorb and emit spectrums shift toward the higher energy, shorter wavelength. That is, the smaller the dot, the more the shift.
NREL study:
By doing detailed thermodynamic calculations, the National Renewable Energy Laboratory, NREL, showed that quantum-dot solar cells operating under concentrated sunlight might have maximum theoretical efficiencies more than doubled that of traditional solar cells up to 66%, compared to 31% for the first- and second-generation solar cells presently.
Here are some of the factual findings from the NREL,
- National Renewable Energy Laboratory, NREL, anticipated in 2001 that quantum dots would be able to produce more than one exciton, or electron-hole pair, from one photon of light, a prediction that was afterwards demonstrated experimentally.
- NREL certified its first all-quantum-dot photovoltaic cell in 2011. This quantum dot was made of lead sulfide. It gave reasonably proper solar cell efficiency and excellent stability. This photovoltaic cell took advantage of quantum-mechanical effects to capture a higher open-circuit voltage than possible from bulk lead sulfide.
- In early 2013, NREL scientists from other labs used a transmission electron microscope at the Environmental Molecular Sciences Laboratory to demonstrate that quantum dots can self-assemble at optimal locations in nanowires. This finding could significantly improve solar cells, quantum computing, and lighting arrays, among other devices.
With advancements and research, it has been found that quantum dot-based applications often outperform traditional solar cells, which benefit from such features.
Solar Cell Applications
Quantum dot-based solar cells have found several immediate applications in the real world. They will revolutionise the following sectors:
- Thin-film solar cells will eventually replace silicon, as the solution processability of quantum dots allows them to be produced as a low-cost solution. Thin-film cells are more flexible and lightweight for solar cells and panels.
- The future of photovoltaics will also include quantum dots. Although it will not replace conventional solar panels for the time being, it will likely complement and supplement them.
Challenges and Ongoing Research
The most significant barrier to commercial feasibility and wide application is the fact that it’s still a work in progress.
Stability and Longevity
The ongoing research is addressing the final critical issues regarding the longevity and stability of quantum dots. The key factor that limits the potential implementation of any quantum dot-based solution is the fact that quantum dots are not stable and can only produce energy for a limited and relatively short time.
Most quantum dots degrade slowly within a few months if unprotected. The key area of research is to make or have already developed protective coatings and encapsulation techniques to mitigate these effects. As a result, they can generate electrical energy for a long time.
Cost Reduction
Another key development currently under research involves the reduction of the production costs of quantum dots. To ensure that quantum dots remain competitive with traditional solar cell technologies, they need to produce quantum dots cost-effectively. Research is looking to achieve this by optimising the synthesis of quantum dots to make such systems more affordable. This will involve looking for cheaper materials to use as precursors with simpler methods of preparing the quantum dots.
Scalability
The other aspect that is under research is the scalability of quantum dot-based solar panels. Researchers are already working with the industry to produce quantum dot solar cells on a scale necessary to satisfy market demands. Today, only a few kilowatts of solar energy are generated from solar panels, although researchers are optimistic that they will be able to scale up manufacturing to provide more energy.
Tandem Solar Cells
Tandem solar cells, which involve using many layers of different materials in order to capture a broader spectrum of sunlight, are still an area of heavy research. Quantum dots could be paired with other high-efficiency materials, such as perovskite cells or traditional silicon solar panels, leading to even higher conversion efficiencies. The value of this research is that it utilises the strengths of different materials to amplify the performance of the whole technology.
Environmental Impact Assessment
Quantum dot solar cells-based studies have also started regarding the process of their lifecycle impact studies. Thus, the benefits and potential risks of quantum dot-based solar panel production, use, and disposal have to be assessed. In the end, the information obtained about this technology is critical for both regulators and policymakers.
- Market Integration: Quantum dot solar cells are likely to be utilised in current solar energy markets and infrastructure, making market integration a significant challenge for researchers.
- Global Standards and Regulations: Finally, global standardisation and regulation overlay for quantum dot solar cells is another area of current research.
Quantum dots are changing the game with various unique properties. When appropriately utilised, these solar nanotechnologies are bound to maximise the efficiency of solar systems in converting light energy. With the numerous trials and tests conducted and the immense potential noted, QDSCs can make a notable difference and major strides in the global aim for clean energy sources.
