Perovskites to make solar energy viable?
Costs of solar energy has fallen by about 77 percent from 2010 to 2018, reaching grid parity in many parts of the world
ENVIRONMENTAL concerns and the rising cost of power generation have forced the world to look at sustainable and environmentally friendly energy resources.
Solar energy is one of the alternatives to fossil fuels, and currently contributes about 103 gigawatt (GW) to the energy needs of the world. Unfortunately, solar energy is hampered by the efficiency and cost-effectiveness of the photovoltaic cells. This has led to numerous innovative efforts to make solar power increasingly competitive with traditional energy sources.
About 90 percent of solar panels in use today consist of mono- and polycrystalline silicon (c-Si) cells, which have dominated the solar market for decades. Polycrystaline silicon has cut the manufacturing costs to some extent, but unfortunately sacrificed some of the efficiency.
The second-generation thin-film solar cells use innovative alternative materials such as copper indium gallium selenide (CIGS) and cadmium telluride (DcTe).
Although they are simpler and cheaper to produce they also tend to sacrifice some efficiency. Currently these ultra thin layer materials did not have a major impact on the market, although thin-film photovoltaic innovations consisting of thin coatings of semiconductor material onto an underlying material did result in an easier incorporation of photovoltaics into buildings.
Over the years researchers have grappled with the problem of efficiency and cost-effectiveness of solar cells. The average efficiency rate of traditional solar cells is approximately 15 percent, meaning that 85 percent of sunlight is not converted into electricity.
Researchers thus constantly experimented with new technologies to increase the efficiency and conversion rate of the solar cells.
However, the relative recent introduction of third generation solar cells containing perovskites may revolutionise the solar energy world. Perovskites are compound materials with a special crystal structure formed through chemistry. They are composed of calcium titanium oxide (CaTiO3) and have a high absorption coefficient that enables ultra-thin films around 500 nanometres (1 nanometre is 1 billionth of a metre).
Interestingly enough, the first perovskite was discovered in the Ural Mountains in western Russia already in 1839 and was named after Count Lev Perovski, a Russian mineralogist. But it was only in 2006 that Tsutomu Miyasaka of Toin University in Japan discovered that some perovskites are semiconductors and could be used as the basis of a new type of solar cell.
In 2009 Japanese researchers were the first to incorporate perovskite in their solar cells, but the solar cells had low efficiencies and lacked stability.
In 2012 Henry Snaith and his fellow researchers from the University of Oxford in the UK found a way to make perovskite solar cells with a light to electricity efficiency of just more than 10 percent, significantly bringing down the cost per watt.
Physicists are constantly enhancing the performance of solar cells to levels never before reached. Over the last two years the efficiency has increased by 20 percent or more, while costing much less than the silicon cells that are predominantly used today.
Dr Yanfa Yan from the University of Toledo in Spain, together with the US National Renewable Energy Lab and the University of Colorado made significant breakthroughs in the chemical formula and processing of tandem (two or more layers) perovskite solar cells.
Professor Yan is convinced that full-sized tandem perovskite solar cells would soon be available in the consumer market.
Using two or more layers of different materials allow for the harvesting of photons from different bands. The higher band gap material on the surface absorbs high-energy photons, while the lower band gap material beneath absorbs the lower-energy photons. These multi-junction cells render much higher efficiencies.
According to their research paper published in 2019 in the academic journal Science Dr Yan and his team fine-tuned a mix of lead and tin through the use of a chemical compound called guanidinium thiocyanate to markedly improve the structural and optoelectronic properties of the lead-tin mixed perovskite films.
This optimisation allowed them to reach an efficiency of 23 percent, which is much higher than the average efficiency of about 15 percent of silicon solar panels.
In addition to the higher efficiency, the perovskite panels also cost less than half of their silicon counterparts.
Solar cells are also not limited to rooftops of buildings anymore. At Nottingham Trent University in the UK researchers developed a way to integrate solar cells into clothing by embedding micro-solar cells into yarn that could then be woven into textiles. This innovation makes it possible for curtains to act as electricity generators.
With perovskite technology, solar energy is becoming more viable and affordable and could protect our planet for our children and future generations.
The costs of solar energy has fallen by about 77 percent from 2010 to 2018, with the result that solar technology reached grid parity in many parts of the world.
Due to the extraordinary increases (above the inflation rate) in the cost of electricity in South Africa, solar energy is a becoming a cost-effective alternative to consumers.
The conventional model of big, centrally distributed electricity (as in the case of Eskom) is globally being replaced by modular and evenly distributed consumer-driven power generation.
Perhaps this may be part of the solution for the struggling, inefficient and expensive Eskom.
Professor Louis C H Fourie is a futurist and technology Strategist. Lfourie@gmail.com