Study describes a novel all-perovskite tandem solar cell which has the potential to provide inexpensive and more efficient way to harness Sun’s energy to generate electrical power
Our reliance on non-renewable source of energy called fossil fuels such as coal, oil, gas has had a tremendous negative impact on mankind and environment. Burning of fossil fuels adds to the greenhouse effect and causes global warming, destroys habitats, causes air, water and land pollution and affects public health. There is an urgent need to build sustainable technology which can help to power the world using clean energy. Solar energy technology is one such method which has the capability to harness Sun’s light – the most abundant renewable source of energy – and convert it into electrical energy or power. The advantageous factors of solar energy in terms of benefitting humans and environment have played a key role in promoting use of solar energy.
Silicon is the commonly used material to make solar cells in solar panels that are available in the market today. The photovoltaic process of solar cells can transform sunlight into electricity without additional use of any fuel. Design and efficiency of silicon solar panels has significantly improved over decades due to advancements in manufacturing and technology. The photovoltaic efficiency of a solar cell is defined as the portion of the energy which is in the form of sunlight and which can be converted into electricity. Photovoltaic efficiency and overall costs are the two main limiting factors in solar panels today.
Apart from silicon solar cells, tandem solar cells are also available in which specific cells are used which are optimized for every section of the Sun’s spectrum thereby leading to increase in overall efficiency. A material called perovskites is considered better than silicon in absorbing high-energy blue photons from sunlight i.e. another part of the Sun’s spectrum. Perovskites are polycrystalline material (generally methylammonium lead trihalide (CH3NH3PbX3, where X is iodine, bromine or chlorine atom). Perovskites are easy to process into sunlight-absorbing layers. Earlier studies have combined silicon and perovskites into solar cells i.e. having silicon cells on the top which can absorb yellow, red and near infrared photons along with perovskite cells thus almost doubling the production of power.
In a new study published in Science on May 3 researchers have for the first time developed all perovskites tandem solar cells which give efficiency of up to 25 percent. This material is called lead-tin mixed low-band gap perovskite film ((FASnI3)0.6 MAPbI3)0.4; FA for formamidinium and MA for methylammonium). Tin has the disadvantage of reacting with oxygen from air creating defects in the crystalline lattice which can disrupt movement of electrical charge in the solar cell thereby limiting cell’s efficiency. Researchers found a way to prevent tin in perovskite from reacting with oxygen. They used a chemical compound called guanidinium thiocyanate to significantly improve structural and optoelectronic properties of lead-tin mixed low-band gap perovskite films. The compound guanidinium thiocyanate coats perovskite crystallites in the solar absorbing film thus preventing oxygen from going inside to react with tin. This straightaway enhances efficiency of the solar cell from 18 to 20 percent. Also, when this new material was combined with conventionally used high-absorbing top perovskite layer, the efficiency further increased to 25 percent.
The current study describes for the first time design of tandem solar cells using all perovskite thin-films and this technology could one day replace silicon in solar cells. The new material is of high quality, is inexpensive and its fabrication is simpler while cost is low compared to silicon and silicon-perovskites tandem cells. Perovskites are man-made material compared to silicon and perovskites based solar panels are flexible, lightweight, and semi-transparent. Although the current material will take some time to surpass efficiency of silicon-perovskite technology. Nevertheless, perovskite-based polycrystalline films have the potential for designing tandem solar cells which could provide efficiency of up to 30percent while keeping other factors unhindered. Further studies are needed to make the material robust, more stable and also recyclable to reduce impact on environment. Solar energy sector is one of the fastest growing and the ultimate goal is to discover a promising alternative for clean energy.
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{You may read the original research paper by clicking the DOI link given below in the list of cited source(s)}
Source(s)
Tong J. et al. 2019 Carrier lifetimes of >1 μs in Sn-Pb perovskites enable efficient all-perovskite tandem solar cells. Science, 364 (6439). https://doi.org/10.1126/science.aav7911
