Solar energy has been growing rapidly over the past decade, with a near 28 fold increase since 2009. This rapid expansion has been driven mainly by a massive reduction in the cost per kilowatt of solar-generated electricity. In many locations, it has become more economical to set up solar arrays than it is to create a new coal or natural gas plant.
However, solar still faces barriers. While many optimistic online presentations state that we could power the entire world with a solar array the size of a small country, these statements are somewhat misleading. Even if we placed such an array in the sunniest location on Earth, energy loss from transmission would negate its ability to power distant regions. Ideally, engineers like to place solar panels as near to the buildings they are powering as possible, in order to minimize distance-related inefficiencies. Many countries simply do not get enough sun for this type of close-proximity installation to be an option.
That said, many such countries would be able to derive energy from the sun if solar panels were more efficient. In this context, efficiency refers to the number of kilowatts generated per unit of incoming solar energy. If solar panels were, say, twice as efficient as they are today, even very cloudy areas would no doubt begin considering them as an energy option. An increase in efficiency would be also a huge boost for the expansion of rooftop solar in sunny countries as well.
The efficiency of silicon-based solar panels has in fact, been on a slow and steady rise since the 70s. These panels, which have so far dominated the solar market, currently enjoy efficiencies of between 15 and 20 percent. These numbers aren’t bad, but there is much room for improvement. Given the human population’s growing demand for energy, and the ever increasing threat of climate change, the world is in desperate need of a solar panel with significantly higher efficiency than today’s models. Unfortunately, given the relatively slow pace at which silicon panels’ efficiency is increasing, they will not be able to fill this role for many years.
There is, however, a promising alternative to silicon panels that has recently been making headlines. That alternative is solar technology made with a crystal called perovskite.
Perovskites are a special type of crystal with a specific type of molecular arrangement. While there are many different types of perovskites, they all share the same general structure. Several of these perovskites have been capturing the attention of materials scientists because of their amazing electrical and photovoltaic properties.
Back in 2009 when research in perovskite-based solar was just beginning, panels made with the crystal showed efficiencies of just around 4%. By 2018, researchers had managed to boost this number to over 24%. No other type of solar technology has seen an efficiency jump of this magnitude in so short a time.
Several other properties add to the appeal of perovskite-based solar. Solar cells containing the crystal are relatively easy and cheap to produce. They may also be suitable for use in applications that silicon-based panels will never be able to fill. Perhaps most importantly, they can generate electricity using wavelengths of light that most of our current commercially available panels cannot harness. Many scientists envision a future where perovskite panels are fused into a layer on top of traditional silicon panels. In this tandem application, perovskite panels would capture part of the incoming light, and let the rest shine through for the silicon panels underneath.
Despite the promise of perovskite panels, there are still many hurdles for developers to overcome before they can become a viable large scale option. One of the biggest is lifespan. While silicon-based panels usually last between 25 and 30 years, perovskite panels created in laboratories are not nearly as long-lived. Even if the efficiency of perovskite panels was twice that of silicon panels, paying customers will not seriously consider this new technology if it cannot last a reasonable period of time. Another issue with perovskite panels has been scalability. The high efficiencies that scientists have observed in perovskite cells were achieved on very small panels (often the size of a postage stamp). When engineers have constructed larger perovskite-based panels, their efficiencies have always been much lower.
The final big obstacle for researchers to overcome is toxicity. At the moment, high efficiency perovskite cells can only be made using relatively toxic compounds, such as lead. While less toxic versions exist, they are also less efficient.
Daunting though these challenges may be, many bright minds are working on solving them. This fact is clearly indicated by graphs showing the number of papers published containing the words “Perovskite solar cells.” In 2011, there was one. In 2013, there were 56. By 2015, there were over 900.
This trend shows no signs of slowing any time soon. While solar’s future is by no means certain, it is looking increasingly likely that this powerful little crystal will play a major role in bringing sun-derived energy to the mainstream market.