After decades of slow (and quite frankly, mostly boring) progress, some long-lost excitement is back to the solar energy community. This excitement is over a new class of materials call “perovskites” that can potentially revolutionize the future of solar energy. Just five years after a big breakthrough in this technology, solar cells based on perovskite materials have seen spectacular improvements in power conversion efficiency (that is, the portion of energy in the form of sunlight that can be converted into electricity). They now rival crystalline silicon solar cells, which have been dominating the markets for the past two decades. With cell efficiencies increasing from just 4% in 2009 to over 22% in early 2017, perovskites have been the fastest-advancing solar technology to date.
Unless you are a mineralogy or materials science enthusiast, chances are you have never heard of perovskites before. However, these materials have been known to scientists for almost two centuries. First identified by German mineralogist Gustav Rose, and named after the Russian mineralogist Lev Perovsky, perovskites are a large family of crystalline materials whose structures are related to the mineral calcium titanate (CaTiO3). A variety of atoms or molecules can bond to create this structure, and therefore perovskites can demonstrate an impressive array of interesting properties including superconductivity and ferroelectricity, which makes them attractive to scientists and engineers in many fields.
Arguably, the most important property of perovskite materials is their ability to convert sunlight into electricity, which also landed them a spot in Science’s Top 10 Breakthroughs of 2013.
A perovskite solar cell is a type of photovoltaic device that includes a perovskite structured compound as the light-harvesting layer. To date, the best performing (laboratory scale) perovskite solar cells utilize a hybrid organic-inorganic lead halide based material. The biggest advantage of such perovskite materials is that they are made using precursors that are rather cheap, commercially available, and easy to produce in large quantities.
The inexpensive materials coupled with simple, low-cost, and low-temperature manufacturing (using liquid solutions, similar to the process of printing a newspaper) make this technology attractive compared to conventional silicon, which requires more complex and energy-intensive manufacturing. A future of perovskite solar modules printed on flexible substrates or even sprayed on window panes is not crazy to imagine. The projected energy payback time for perovskite solar modules, which is the time necessary for them to generate energy equivalent to what went into producing them, was found in recent studies to be less than 1 year. This is a great advantage over the reigning silicon technology for which energy payback time is estimated somewhere between 3 to 4 years. Finally, as a result of the tunable chemical composition of perovskites, a range of colors can be achieved. This offers the opportunity to make colorful, more aesthetically pleasing modules which can potentially be complementary to existing solar technologies (since the color of the solar cell depends on the part of the solar spectrum absorbed by the light-harvesting material).
Unfortunately, like every other emerging technology, perovskites have some battles to win before they can attempt to usurp commercial silicon solar panels. The biggest question mark holding perovskite technology from commercialization is the stability of the cells over their operational lifetime. A variety of both internal as well as environmental factors (such as humidity) were found to impact the stability of perovskites and lead to efficiency degradation over time. The good news is that advanced encapsulation procedures (common in electronics manufacturing) can nearly eliminate degradation due to the environment. More alarming and substantially more complicated to solve are the potential intrinsic material instabilities that are active even under inert conditions. Such instabilities can originate, for example, from undesirable chemical interactions between the different layers that constitute a fully operational solar cell, leading to efficiency degradation. Another issue yet to be fully addressed is the use of lead (a highly toxic heavy metal) in perovskite compounds. The extraction, use, and disposal of lead can severely impact both humans and the environment, which is why researchers have been exploring options for lead-free perovskites, with tin being the current runner-up.
The exceptional performance of hybrid perovskite materials might signify a new era in the field of solar energy with cheap, light-weight, and vibrant solar panels replacing black and rigid silicon. With new and exciting advances in both efficiency and stability surfacing every day and with the world’s greatest scientists and entrepreneurs invested in it, perovskites can surely compete in the race for “technology of the future” in the sustainable energy category.
Iordania Constantinou (email@example.com)
Current position: Heidelberg University, Postdoctoral Fellow in Molecular Biology working on the development of instrumentation for high throughput fluorescence imaging.
Postgraduate Education: University of Florida, PhD in Materials Science and Engineering with specialization in organic electronic materials for light harvesting.
Undergraduate Education: Cyprus University of Technology, BS in Mechanical Engineering.