July 2022

University of New South Wales (UNSW) team, led by renowned PV scientist Martin Green, have shown that perovskite solar cells may be especially susceptible to damage from reverse bias, caused by uneven shading or other issues that may appear in real-world environments. Both the reverse-bias itself and resulting build up of heat can cause several of the materials commonly used in perovskite solar cells to degrade, and these issues have received only limited attention in research published thus far. 

Stability issues with perovskite solar cells linger, despite impressive research achievements in the last few years. Much of the research focused on improving stability to date has focused on the issues that arise under normal operating conditions – for example sensitivity to oxygen and moisture, which can be solved through encapsulation, or degradation under UV light, which can be solved with reflective coatings. Other issues, however, may present serious challenges to developing perovskite devices that can function in outdoor conditions for years and even decades. “…thermal degradation and reverse-bias instability are remaining issues that pose challenges even for intrinsically much more stable silicon cells, suggesting that innovative approaches may be required to satisfactorily address these for perovskite cells”, explain the authors of the new paper.

Researchers led by Prof. LIU Shengzhong from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) have developed a facile surface redox engineering (SRE) strategy for vacuum-deposited NiOx to match the slot-die-coated perovskite, and fabricated high-performance large-area perovskite submodules.

Inverted PSCs could be even more valuable than their normal counterparts because the former have easily-mitigated hysteresis behavior and long-term durability. NiOx has been demonstrated as a promising hole transport material for inverted PSCs. But for most vacuum-processed NiOx films, the relatively hydrophobic surface attenuates the adhesion of perovskite ink, making it challenging to deposit large-area perovskite films.

Researchers from Hebei University, Karlsruhe Institute of Technology and Chinese module manufacturer Yingli Green Energy Holding Co. Ltd. have reported a heterojunction solar cell based on graphene-oxide (GO) and silicon with a large area of 5.5 cm².

GO is a compound of carbon, oxygen and hydrogen that is obtained by treating graphite with oxidizers and acids. It consists of a single-layer sheet of graphite oxide that is commonly used to produce graphene-related nanomaterials for various applications, including electronics, optics, chemistry and more. The scientists developed an ink made of GO mixed with Nafion, that can be spin-coated on an n-type silicon wafer to form a high-quality passivating contact scheme. “Low interface recombination is provided by the Nafion and carrier selection by the GO,” the team explained, noting that the passivation scheme also includes an electron-selective passivation contact comprising n-doped hydrogenated amorphous silicon with an indium tin oxide (ITO) overlayer aimed at improving light trapping and reducing surface recombination.

The U.S. Department of Energy Solar Energy Technologies Office (SETO) selected University of Arizona chemical and environmental engineering associate professor Erin Ratcliff for a $300,000 grant to advance the near-term scalability of perovskites.

“Perovskites are the highest-performing printable solar cell technology,” Ratcliff said. “But the operating hypothesis in the field is that defects are contributing to instability”. With the SETO grant, Ratcliff and her team will develop a method for detecting these defects during manufacturing. The low-cost, scalable method will help scientists understand the way different parts and materials of the manufacturing process may contribute to defects and instability, and, in turn, how to mitigate these effects. The grant is part of SETO’s Small Innovative Projects in Solar 2022 Funding Program, which funds targeted, early-stage ideas in solar energy research that can produce significant results within the first year of performance. Nineteen projects received a total of $5 million in funding.

Researchers from Nagoya Institute of Technology in Japan have used a combination of experimental and theoretical methods to better understand the optical, electronic, and magnetic properties of complex solids of layered perovskite compounds. The approach is applicable to a wide range of functionalized crystalline ceramic compounds.

Urban areas without sufficient tree coverage are significantly warmer than their surroundings. This "urban heat island" effect mainly results from an absorption of near-infrared (NIR) radiation in sunlight. NIR-reflective pigments that can mitigate such heating effects are, therefore, highly desirable. In particular, functional inorganic pigments are attractive candidates on this front. In fact, Dr. Ryohei Oka and his colleagues from Nagoya Institute of Technology have demonstrated that layered perovskite ceramic compounds of the type A₂BO₄ are ideal for reflecting NIR. In his previous study, it was discovered that novel perovskites such as titanium-added calcium manganese oxide (Ca₂(Mn,Ti)O₄) ceramics are much better at reflecting NIR radiation than commercially available black pigments. However, the mechanism by which Ca₂(Mn,Ti)O₄ achieves this goal remains unknown.

Researchers from the Karlsruhe Institute of Technology (KIT) and the Forschungszentrum Jülich GmbH in Germany have developed a monolithic perovskite-silicon solar cell with a power conversion efficiency of 20%, using a novel lamination approach.

The team investigated how this lamination process can be applied to perovskite/silicon tandem technology. They explained that the solar cells are the first prototypes and that lamination is a suitable alternative fabrication method for monolithic perovskite/silicon tandem solar cells. The lamination approach, they said, is particularly interesting for perovskite-based PV, as it notably increases the degree of freedom in the choice of materials and accessible deposition techniques.

Researchers from Switzerland's Federal Laboratories for Materials Science and Technology (EMPA) and École Polytechnique Fédérale de Lausanne (EPFL) have designed a four-terminal tandem mini-module based on perovskite and copper, indium, gallium and selenium (CIGS) with an aperture area of around 2 cm², and a geometric fill factor of over 93%.

Processing sequence of flexible NIR-transparent perovskite mini-module. Image from RRL Solar

The team reports that the key to efficient flexible perovskite-CIGS tandem modules is the development of near-infrared (NIR) transparent perovskite solar modules on a flexible polymer foil. To achieve these results, the researchers had to overcome the challenges of laser patterning on flexible substrates to realize the first all-laser scribed monolithically interconnected NIR-transparent perovskite mini-modules on polymer film. The perovskite mini-module used in the tandem panel was fabricated on a flexible polyethylene napthalathe (PEN) substrate mounted to a glass substrate in a p–i–n device architecture. This configuration, according to the research team, shows reduced absorption in the NIR region.

Researchers from the Eindhoven University of Technology, the Netherlands Organization for Applied Scientific Research (TNO), and Indian steel manufacturer Tata Steel recently fabricated an inverted perovskite solar cell based on a polymer-coated steel substrate that can achieve a power conversion efficiency approaching that of non-inverted reference solar cells with a similar stack design.

Substrate (A and B) and superstrate (C) p–i–n solar cells on glass (A and C) and steel (B). Image from ACS Publication study

The cell has a p-i-n structure and relies on nickel-plated steel coated with a polyamide-imide (PAI) planarization layer, which serves as an insulating layer. The researchers used an opaque titanium electrode covered with a thin sputtered indium tin oxide (ITO) layer to enable the binding of the phosphonic acid anchoring groups of the monolayer based on a perovskite known as 2PACz, which serves as a hole-collecting electrode.

Researchers from Ulsan National Institute of Science and Technology (UNIST) in South Korea and the University of Pittsburgh in the U.S have reported a power conversion efficiency of 23.5% in a perovskite-silicon tandem solar cell by applying a special textured anti-reflective coating (ARC) polymeric film.

The team prepared the multifunctional film with phosphor particles measuring 10 μm in diameter. They are able to block ultraviolet (UV) light and silicon dioxide (SiO₂) nanoparticles with a diameter of 10 nm to increase the ability of a perovskite-silicon tandem solar cell to absorb visible light. The scientists explained that the phosphors increase the reflectance of the ARC film, due to their large particle size, thus causing a backward light scattering issue. This in turn is compensated by the addition of the spherical SiO₂ nanoparticles.

A Chinese startup called DaZheng (Jiangsu) Micro-Nano Technologies has announced that it has reached mass production of large, flexible perovskite solar panels, based on technology that was initially developed by researchers in Japan.

DaZheng (Jiangsu) Micro-Nano Technologies reportedly invested 80 million yuan (around USD$11.85 million) to build a production line with an annual capacity of 10 megawatts in Jiangsu Province. The 40 cm by 60 cm panels will be cut into smaller pieces and shipped to smartphone and tablet makers in China.