What are perovskite?
Perovskites are a class of materials that share a similar structure, which display a myriad of exciting properties like superconductivity, magnetoresistance and more. These easily synthesized materials are considered the future of solar cells, as their distinctive structure makes them perfect for enabling low-cost, efficient photovoltaics. They are also predicted to play a role in next-gen electric vehicle batteries, sensors, lasers and much more.
How does the PV market look today?
In general, Photovoltaic (PV) technologies can be viewed as divided into two main categories: wafer-based PV (also called 1st generation PVs) and thin-film cell PVs. Traditional crystalline silicon (c-Si) cells (both single crystalline silicon and multi-crystalline silicon) and gallium arsenide (GaAs) cells belong to the wafer-based PVs, with c-Si cells dominating the current PV market (about 90% market share) and GaAs exhibiting the highest efficiency.
Thin-film cells normally absorb light more efficiently than silicon, allowing the use of extremely thin films. Cadmium telluride (CdTe) technology has been successfully commercialized, with more than 20% cell efficiency and 17.5% module efficiency record and such cells currently hold about 5% of the total market. Other commercial thin-film technologies include hydrogenated amorphous silicon (a-Si:H) and copper indium gallium (di)selenide (CIGS) cells, taking approximately 2% market share each today. Copper zinc tin sulphide technology has been under R&D for years and will probably require some time until actual commercialization.
What is a perovskite solar cell?
An emerging thin-film PV class is being formed, also called 3rd generation PVs, which refers to PVs using technologies that have the potential to overcome current efficiency and performance limits or are based on novel materials. This 3rd generation of PVs includes DSSC, organic photovoltaic (OPV), quantum dot (QD) PV and perovskite PV.
A perovskite solar cell is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer. Perovskite materials such as methylammonium lead halides are cheap to produce and relatively simple to manufacture. Perovskites possess intrinsic properties like broad absorption spectrum, fast charge separation, long transport distance of electrons and holes, long carrier separation lifetime, and more, that make them very promising materials for solid-state solar cells.
Perovskite solar cells are, without a doubt, the rising star in the field of photovoltaics. They are causing excitement within the solar power industry with their ability to absorb light across almost all visible wavelengths, exceptional power conversion efficiencies already exceeding 20% in the lab, and relative ease of fabrication. Perovskite solar cells still face several challenge, but much work is put into facing them and some companies, are already talking about commercializing them in the near future.
What are the advantages of Perovskite solar cells?
Put simply, perovskite solar cells aim to increase the efficiency and lower the cost of solar energy. Perovskite PVs indeed hold promise for high efficiencies, as well as low potential material & reduced processing costs. A big advantage perovskite PVs have over conventional solar technology is that they can react to various different wavelengths of light, which lets them convert more of the sunlight that reaches them into electricity.
Moreover, they offer flexibility, semi-transparency, tailored form factors, light-weight and more. Naturally, electronics designers and researchers are certain that such characteristics will open up many more applications for solar cells.
What is holding perovskite PVs back?
Despite its great potential, perovskite solar cell technology is still in the early stages of commercialization compared with other mature solar technologies as there are a number of concerns remaining.
One problem is their overall cost (for several reasons, mainly since currently the most common electrode material in perovskite solar cells is gold), and another is that cheaper perovskite solar cells have a short lifespan. Perovskite PVs also deteriorate rapidly in the presence of moisture and the decay products attack metal electrodes. Heavy encapsulation to protect perovskite can add to the cell cost and weight. Scaling up is another issue - reported high efficiency ratings have been achieved using small cells, which is great for lab testing, but too small to be used in an actual solar panel.
A major issue is toxicity - a substance called PbI is one of the breakdown products of perovskite. This is known to be toxic and there are concerns that it may be carcinogenic (although this is still an unproven point). Also, many perovskite cells use lead, a massive pollutant. Researchers are constantly seeking substitutions, and have already made working cells using tin instead. (with efficiency at only 6%, but improvements will surely follow).
While major challenges indeed exist, perovskite solar cells are still touted as the PV technology of the future, and much development work and research are put into making this a reality. Scientists and companies are working towards increasing efficiency and stability, prolonging lifetime and replacing toxic materials with safer ones. Researchers are also looking at the benefits of combining perovskites with other technologies, like silicon for example, to create what is referred to as “tandem cells”.
Commercial activity in the field of perovskite PV
In September 2015, Australia-based organic PV and perovskite solar cell (PSC) developer Dyesol declared a major breakthrough in perovskite stability for solar applications. Dyesol claims to have made a significant breakthrough on small perovskite solar cells, with “meaningful numbers” of 10% efficient strip cells exhibiting less than 10% relative degradation when exposed to continuous light soaking for over 1000 hours. Dyesol was also awarded a $0.5 million grant from the Australian Renewable Energy Agency (ARENA) to commercialize an innovative, very high efficiency perovskite solar cell.
Also in 2015, Saule Technologies signed an investment deal with Hideo Sawada, a Japanese investment company. Saule aims to combine perovskite solar cells with other currently available products, and this investment agreement came only a year after the company was launched.
The latest perovskite solar news:
Researchers from Florida State University and Georgia Tech have been working on new ways for solar cells to absorb and use infrared light, a portion of the solar spectrum that is typically unavailable for solar cell technology.
“We’re working on a process to optimize the efficiency of solar cells,” said Assistant Professor of Chemistry and Biochemistry Lea Nienhaus. “The main drive is to optimize this process for solar applications”. The team has created a new approach for solar cells to facilitate a process called photon upconversion. In photon upconversion, two low energy photons are converted into one high-energy photon that emits visible light.
Researchers from the University of Surrey’s Advanced Technology Institute (ATI) have produced a perovskite solar cell which contains 50% less lead, replaced with the more innocuous tin. By fine-tuning their tin solar cell, the researchers were able to create a product that is able to absorb infrared light in a similar manner as silicon cells. They also found that by stacking lead-only cells with the ones mixed with tin can lead to power conversion results that outperform those of silicon-only power cells.
Indrachapa Bandara, lead author of the study and PhD student at ATI, said: “We are starting to see that many countries are treating the threat of climate change with the seriousness it deserves. If we are to get a handle on the problem and put the health of our planet on the right track, we need high-performing renewable energy solutions.... Our study has shown that tin based perovskite solar cells have an incredible amount of potential and could help countries such as the United Kingdom reach its target of becoming carbon neutral by 2050”.
An international research team led by the University of Houston researchers have tackled a lingering question about how a two-dimensional perovskite crystal composed of cesium, lead and bromine emits a strong green light. Crystals that produce light on the green spectrum are desirable because green light, while valuable in itself, can also be relatively easily converted to other forms that emit blue or red light, making it especially important for optical applications ranging from light-emitting devices to sensitive diagnostic tools.
There was, however, confusion as to how the crystal, CsPB2Br5, produced the green photoluminescence. Several theories emerged, without a definitive answer. Now, the researcher team from the United States, Mexico and China, led by the University of Houston, have reported that they have used sophisticated optical and high-pressure diamond anvil cell techniques to determine not only the mechanism for the light emission but also how to replicate it.
Researchers at the lab of Anders Hagfeldt at EPFL, working with colleagues at the lab of Michael Grätzel, brought real-world conditions into the controlled environment of the lab. Using data from a weather station near Lausanne (Switzerland), they reproduced the real-world temperature and irradiance profiles from specific days during the course of the year, to test PSCs in real-world conditions.
With this approach, the scientists were able to quantify the energy yield of the devices under realistic conditions. “This is what ultimately counts for the real-world application of solar cells," says Dr. Wolfgang Tress from EPFL.
An international team of clean chemistry researchers, led by Professor Joseph Shapter and Flinders University, has made very thin phosphorene nanosheets for low-temperature perovskite solar cells (PSCs) using the rapid shear stress of the University’s revolutionary vortex fluidic device (VFD). This new nanomaterial made from phosphorus, may turn out to be a key ingredient for more sustainable and efficient next-generation PSCs.
“Silicon is currently the standard for rooftop solar, and other solar panels, but they take a lot of energy to produce them. They are not as sustainable as these newer options,” says adjunct Professor Shapter, now at University of Queensland.