Technical / research - Page 36

Scientists from Germany’s Helmholtz-Zentrum Berlin (HZB) and HTW Berlin have examined how precursor inks influence the quality of perovskite thin films. The best cells were scaled up to minimodule size. The team showed that when slot-die coating the halide perovskite layers on large areas, ribbing effects may occur but can be prevented by adjusting the precursor ink's rheological properties.

Prof. Dr. Eva Unger's team at Helmholtz-Zentrum Berlin has extensive expertise in solution-based processing methods and is investigating options for upscaling. "Perovskite photovoltaics is the best solution-processable PV technology available," says Eva Unger, "but we are only just beginning to understand how the complex interaction of the solvent components affects the quality of the perovskite layers."

A team of scientists at Swansea University has used a combination of a low-temperature device structure and roll-to-roll-compatible solution formulations to make a fully roll-to-roll (R2R) printable device architecture overcoming interlayer incompatibilities and recombination losses.

A sample of the new fully roll-to-roll (R2R) coated device. Credit: Swansea University (from Techxplore)

This means that using slot die coating in a R2R process, the team from the SPECIFIC Innovation and Knowledge Center at Swansea University has established a way to create "fully printable" perovskite photovoltaics.

Scientists China's Zhengzhou University,  Xi'an Jiaotong University and Chinese Academy of Sciences (CAS) have designed a solar cell based on low-dimensional Ruddlesden-Popper (LPDR) perovskite that is said to have improved carrier transport properties.

The team explained that the new cells are more stable compared to regular 3D perovskite solar cells and are suitable for building-integrated photovoltaics (BIPV), conventional solar, and wearable devices.

Researchers at  the University of Oxford and the University of Potsdam have combined theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (VOC) and short-circuit current (JSC) conditions.

A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external VOC is detrimental for these devices. The team demonstrated that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n-interface, suppressing the QFLS-VOC mismatch, and boosting the VOC.

The human brain can effortlessly process complex sensory information and learn from experiences, while a computer cannot. And, the brain does all this by consuming less than half as much energy as a laptop. One of the reasons for the brain's energy efficiency is its structure. The individual brain cells – the neurons and their connections, the synapses – can both store and process information. In computers, however, the memory is separate from the processor, and data must be transported back and forth between these two components. The speed of this transfer is limited, which can slow down the whole computer when working with large amounts of data.

One possible solution to this problem are novel computer architectures that are modeled after the human brain. To this end, scientists are developing 'memristors': components that, like brain cells, combine data storage and processing. A team of researchers from Empa, ETH Zurich and the Politecnico di Milano has developed a memristor based on perovskite materials that is more powerful and easier to manufacture than its predecessors.

Researchers at Huazhong University of Science and Technology, Wuhan University of Technology and University of Toronto recently introduced a new approach for fabricating more stable 3D/2D heterostructures, preventing their degradation. Their approach is based on the introduction of an additional layer between the structures; 3D and 2D perovskite layers.

2D and quasi-2D modified 3D perovskite heterostructures (i.e., structures comprised of 3D and 2D perovskite materials) have several advantageous qualities, such as enabling the passivation of defects and a favorable band alignment, which improve a perovskite solar cells' open-change voltage and fill factor. 3D/2D heterostructures are typically created by spin coating an organic cation salt solution on top of a 3D perovskite material and forming a thin 2D perovskite layer on its surface. This process, however, can facilitate the subsequent degradation of the heterostructures in some conditions, due to the diffusion of ions between the 2D perovskite surface and underlying bulk 3D perovskite.

Scientists from Skoltech (Skolkovo Institute of Science and Technology), Research Centre for Medical Genetics, Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry and Zhengzhou Research Institute of HIT have studied the toxicity of materials used in perovskite solar cells.

They concluded that once the remaining technological hurdles are overcome, mass production of this potentially cheap and efficient alternative to silicon-based photovoltaics should not cause any significant environmental risks and health hazards. The study draws attention to perovskite components other than lead, suggesting that metal's toxicity, by comparison, could be overestimated.

Nano-textured surfaces are an interesting approach for optimizing the optical characteristics for monolithic perovskite/silicon tandem solar cells. Scientists from Germany’s Helmholtz-Zentrum Berlin (HZB) have examined the development of different textures of silicon surfaces using various commercial additives and their performance in silicon heterojunction (SHJ) and SHJ–perovskite tandem solar cells.

The team performed optical and electrical characterization and found that nano-textured surfaces can compete with standard textured surfaces, yielding higher average efficiencies in single junctions. In addition, their compatibility with solution-processed perovskite top cells was demonstrated in the recent study, yielding a perovskite/silicon tandem solar cell efficiency of >28% on a bottom cell with nano-texture on both sides.

Researchers at South Korea’s Ulsan National Institute of Science and Technology (UNIST), Chonnam National University and Pohang University of Science and Technology (POSTECH) have developed a unique perovskite solar cell that uses alkylammonium chloride (RACI) to control the formation of defects in the perovskite layer.

The US National Renewable Energy Laboratory (NREL) has certified the South Korean research team's cell's 25.73% efficiency. The champion device built by the scientists reached an efficiency of 26.08%.

Researchers from North Carolina State University, Pennsylvania State University and University of North Carolina at Chapel Hill have found that channeling ions into defined pathways in perovskite materials improves the stability and operational performance of perovskite solar cells. 

The team's recent study presented a multiscale diffusion framework that describes vacancy-mediated halide diffusion in polycrystalline metal halide perovskites, differentiating fast grain boundary diffusivity from volume diffusivity that is two to four orders of magnitude slower.