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The Promise of Solar Cells
Currently the fastest growing source of renewable energy powering an average of 158 million homes and employing over 3 million people globally, Solar cells (also known as photovoltaic cells) offer a promising solution for the future. By efficiently converting sunlight into electricity, solar cells employ the use of silicon, a semiconductor material, to absorb photons from the sun and produce a flow of electrons or an Electric current.
The absorption of the photon transfers its energy to an electron within the material. This excites the electron, allowing it to break bonds and produce an electric current. The imposition of a built-in electric field causes a flow of electrons to move in opposite directions, producing a DC current which can be used by devices or stored in batteries.
To further elaborate on the mechanism of solar cells, it is important to understand the photovoltaic effect. The photovoltaic effect is the process of generating voltage when exposed to sunlight; this is made possible by two different types of semiconductors (p-type & n-type) that are joined to create a p-n junction. The p-type region has an excess of positively charged holes, whereas the n-type region has an excess of negatively charged electrons. The diffusion of electrons across the junction creates a depletion region.
In a solar cell, the p-type region is intercalated with boron, an element that has one less valence electron compared to silicon whereas the n-type region is doped with phosphorus, an element with one additional valence electron compared to silicon atoms.
When the cell is then exposed to sunlight, the photons – which are essentially carriers of electromagnetic radiation (energy) transfer their energy to the electrons in the p-n junction. The transfer of energy excites the electron allowing it to jump to a conduction band, which is simply a higher energy state. As the electron jumps from the valence band to the conduction band, a ‘hole’ is created in the valence band, resulting in an electron-hole pair. With the implementation of a p-n junction, the electric field separates the electrons and holes, where the freed electrons move to the n-side instead of the p-side and the hole moves to the opposite direction to the p-side. This movement of electrons results in the generation of current in the cell.
The mechanism behind solar cells is what makes them the world's most preferred source of renewable energy. From a technological standpoint, solar cells are a wonder for all our energy needs. They offer many advantages, including reduced greenhouse gas emissions and less dependence on fossil fuels making them an environmentally friendly alternative.
Furthermore, the cost of solar panels has decreased significantly by almost 80%, making them a more economically viable option for businesses and individuals. In a nutshell, the benefits of solar cells are clear: they are clean, renewable, and cost effective.
However, every invention has its limitations, and solar cells are no exception. The potential of solar cell technology may be hindered by a number of factors, including large scale land use, weather dependence, energy storage challenges, geographical limitations, and hidden environmental impacts. For example, solar cells require a significant amount of land, which can exacerbate existing issues related to soil and habitat conservation. Additionally, the disposal of solar cells at the end of their life can result in the release of toxic chemicals and greenhouse gasses, which raises the question about whether this technology truly qualifies as ‘renewable’.
In addition to this, such processes only account for 25% efficiency, and even with advancements in multi-junction solar cells, the efficiency has only reached a maximum of 40% efficiency in a laboratory setting. This is caused due to the materials used, the amount of reflection which leads to a significant amount of sunlight lost from the surface, and losses of electricity due to electrical contacts. However, issues regarding efficiency and its environmental implications are not a dead end.
Materials that are more light absorbent such as perovskites can be used to enable an absorption of a range of wavelengths. Issues regarding reflection can be solved using surface texturing or using anti reflective coatings, further to this- enhancing electrical contacts can reduce the loss of electricity. To address the land issue, using areas that are not suitable for other activity or even designing solar cells that are more efficient for land by integrating photovoltaics (BIPV) or concentrating solar power (CSP) can be an alternative. In terms of the toxic chemicals, developing methods to recover chemicals can allow the recycling and the proper disposal of chemicals. Perovskites are also more sustainable. The basic crux of the problem lies in its efficiency; the more efficient we make it, the less we need to manufacture and the less we need to dispose of.
To conclude, Solar cells provide a bright future in terms of its potential for efficiency, cost effectiveness and sustainable energy generation. The ongoing development of new designs and materials can enhance its working potential and can live up to its poised reputation as the future of sustainable energy.
By- Diya Madhusoodan