Stability - Page 16

Researchers from Ulsan National Institute of Science and Technology (UNIST), Wuhan University of Technology and Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratory have announced their success in manufacturing a high-efficiency, stable perovskite solar cell through a vacuum thin film deposition process.

Vacuum thin film deposition is a technique that is already widely used in the manufacture of large OLED TVs by evaporating raw materials in a vacuum and coating them thinly on a substrate. The perovskite solar cell developed this way displayed a photovoltaic-to-electricity conversion efficiency of 21.4%, which the team said is the highest among perovskite solar cells manufactured by vacuum thin film deposition process.

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.

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.

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.

Tokyo Chemical Industry (TCI) is a global supplier of laboratory chemicals and specialty materials. TCI is a leading the next-generation solar technology industry by providing high-quality and reliable materials, including metal halide perovskite precursors such as lead/tin halides and organic onium salts, as well as carrier transporting materials.

TCI recently launched hole selective self-assemble monolayer (SAM) forming agents, 2PACz [Product Number: C3663] , MeO-2PACz [Product Number: D5798] and Me-4PACz [Product Number: M3359] for high performance perovskite solar cells. The company is getting ready to launch some more related materials in 2022. We thought it'd be a good time to catch up with TCI, and have conducted a Q&A with TCI’s Institute for Material Science's general manager, Dr. Taro Tanabe.

Researchers at King Abdullah University of Science and Technology (KAUST) and Max Planck Institute have developed an inverted perovskite-silicon tandem solar cell with a 1 nm thick interlayer based on magnesium fluoride (MgFx) placed between the perovskite layer and the hole transport layer (HTL), in order to reduce voltage losses while still retaining 95.4% of its initial efficiency after 1,000 hours.

The scientists stated that the charge transport and recombination interfaces could be carefully tuned with MgFx interlayers, enabling a certified efficiency of 29.3%. Currently, the record perovskite/silicon tandem solar cell is a 29.8% device that was recently developed by scientists at Helmholtz-Zentrum Berlin (HZB) in Germany. The scientists fabricated the new cell with a sub-cell based on crystalline silicon wafers with double-side texture, which they say reduces front reflection while improving light trapping. They also placed the MgFx interlayer at the electron-selective top contact.

An international group of researchers from Swansea University, Indian Institute of Technology, University of Jammu, CSIR and Khalifa University of Science and Technology recently examined how down-conversion (DC) materials could be used to improve the performance of solar cells based on perovskite materials. The team reported that such materials could result in an electric yield enlargement by converting ultraviolet (UV) light to visible, while also providing UV shielding.

“The DC materials can absorb the high-energy photon (300–500 nm) and re-emit a longer-wavelength photon to which the photovoltaic (PV) device is more sensitive,” the team said. “Various types of DC materials have been investigated for this purpose like quantum dots (QDs), oxides, luminescent glasses, lanthanides, and organic dyes.”

The CEA at INES has reported the design of flexible perovskite solar modules with a surface area of 11.6 cm² and a power conversion efficiency of 18.9% (stabilized efficiency > 18.5%). This performance is said to be a world record for flexible perovskite modules over 10 cm².

Perovskite-based modules before and after flexible encapsulation. Image credit: CEA

For some applications, the use of flexible substrates may be attractive for single-junction perovskite technology as it opens the way to high-speed, low-temperature printing processes. Thus, it becomes possible to use low cost substrates whereas inorganic flexible technologies, such as CIGS, require higher temperature processes and substrates that are more expensive. Many teams around the world are trying to meet the challenges of making larger area devices with sufficient stability for real-life applications. This is one of the tasks standing before partners of the European APOLO project, as part of which these results were obtained.

Researchers from Princeton University in the U.S and Sweden's Linköping University have reported the development of "the first perovskite solar cell with a commercially viable lifetime". The team estimates their device can perform above industry standards for around 30 years, far more than the 20 years used as a threshold for viability for solar cells.

Not only is the device said to be highly durable, but it also meets common efficiency standards. It is the first of its kind to rival the performance of silicon-based cells, which have been market leaders for decades.