Perovskite Solar - Page 59

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.

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.

TubeSolar, together with the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW), has reached an important milestone on the way to industrial production of its novel photovoltaic technology: an efficiency record of 14% was achieved on solar films in the industrially suitable "roll-to-roll" process. This was achieved as part of TubeSolar's perovskite research activities. 

In the process, the partners deposited all layers - with the exception of the front and rear contacts - using slot die. The speed of the coating process was over one metre per minute. The combination of this industrially suitable, fast production process and the high efficiency was referred to as 'groundbreaking' by the Companies. The flexible solar cells are used for the production of tubular photovoltaic modules, which can be used in agri-photovoltaics, among other applications.

A research team, led by Prof. Zhou Huiqiong's group from the National Center for Nanoscience and Technology (NCSNT) of the Chinese Academy of Sciences (CAS), has developed a strain relaxation strategy to study the effect of residual strain on properties of quasi-two-dimensional (2D) perovskites. 

The introduction of hydrophobic spacer cations makes quasi-2D perovskites more stable compared with traditional 3D perovskites, but the stability of perovskites remains unsatisfactory. Residual strain is closely related to the crystallographic properties, which in turn can significantly affect the photovoltaic properties and stability of perovskites. The research team investigated the residual strain in quasi-2D perovskite with mixed spacer cations by X-ray diffraction (XRD) and atomic force microscope (AFM). They found that there is severe tensile strain along the out-of-plane direction in pristine perovskite film, leading to poor crystallinity and insufficient stability issues. With an appropriate composition of spacer cations, the tensile strain is effectively released.