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:
Kyushu University team develops a surface treatment method for perovskite cells with reduced hysteresis
Researchers in Japan's Kyushu University have modified the tin(IV) oxide layer of a perovskite device with a fullerene-derivative-based self-assembled monolayer to produce a cell they claim offers stability and a reduction in the hysteresis effect which makes predicting power output so tricky.
The Kyushu University team has developed a surface treatment method for perovskite cell production they say reduces hysteresis – an effect which afflicts perovskite devices because their output depends on a variety of previous inputs rather than just their immediate condition, rendering performance less predictable. In perovskite cells, hysteresis is strictly dependent on the composition of the material. Ion migration and non-radiative recombination near interfaces are generally considered responsible for the effect.
New precision spray-coating method enables layered deposition of different perovskite materials for stacked architectures
A team of researchers from Mahidol University, Chiang Mai University and PERCH-SIS Institute in Thailand has developed a new precision spray-coating method that enables more complex perovskite solar cell designs and could be scaled up for mass production.
The researchers demonstrated the technique by depositing a perovskite material with higher stability on different perovskite material with better electrical properties. Applying different perovskite materials in each layer can be used to customize a device’s properties or meet specific performance and stability requirements.
A UNIST research team has developed an electrode that can significantly improve the stability of perovskite solar cells. UNIST announced that its research team developed “flexible and transparent metal electrode-based perovskite solar cells with a graphene interlayer”.
The team suppressed interdiffusion and degradation using a graphene material with high impermeability, the team said. Team leader professor Hyesung Park commented that the research will greatly help not only solar cells but other perovskite-based flexible photoelectric devices such as LEDs and smart sensors.
Australian scientists have announced what could be an important step towards commercial viability of perovskite solar cells when their solar cells passed strict International Electrotechnical Commission testing standards for heat and humidity.
"Perovskites are a really promising prospect for solar energy systems," said Professor Anita Ho-Baillie, the inaugural John Hooke Chair of Nanoscience at the University of Sydney. "They are a very inexpensive, 500 times thinner than silicon and are therefore flexible and ultra-lightweight. They also have tremendous energy enabling properties and high solar conversion rates." However, unprotected perovskite cells do not have the durability of silicon-based cells, which is one of the reasons they are not yet commercially viable.
Australia's Monash University researchers have designed a new system incorporating 3D-printed key components, that could speed up tests on new designs for perovskite solar cells. The machine can reportedly analyze 16 sample perovskite-based solar cells simultaneously, in parallel, dramatically speeding up the process.
The invention means that the performance and commercial potential of new compounds can be very rapidly evaluated, significantly speeding up the development process. "Third generation perovskite cells have boosted performance to above 25 percent, which is almost identical to the efficiency level for conventional silicon-based ones," said project leader Adam Surmiak from the ARC Centre of Excellence in Exciton Science (Exciton Science).