Technical / research - Page 48

The Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) has made progress towards the goal of coating large-area perovskite solar cells on an industrial scale using a process that uses more benign solvents than available hazardous solvents like dimethylformamide. The team of researchers developed a coating process for perovskites that uses a single ecofriendly solvent, dimethyl sulfoxide. The ZSW team applied this method to produce a solar cell nearly as efficient as cells made with the toxic solvent. 

Perovskite precursors have to first be dissolved so they can be applied in uniform layers to the substrate. This requires solvents that usually contain dimethylformamide (DMF), which is hazardous to health and the environment. This toxicity hampers efforts to scale this process up to industrial production. Manufacturers would have to produce and dispose of larger quantities of the solvent and take even more stringent occupational safety measures, also causing costs to rise. For these reasons, many researchers and manufacturers are in search of environmentally compatible solvents that are suitable for industrial applications. This use case requires chemical properties that very few substances exhibit. Dr. Jan-Philipp Becker, the head of the ZSW’s Photovoltaics: Materials Research department, worked with his team to investigate pure dimethyl sulfoxide (DMSO) to see if it could serve this purpose.

A research group that includes scientists from Chinese module manufacturer JinkoSolar, Australian National University, the Beijing Institute of Technology and Peking University has developed a monolithic perovskite-silicon n-type tandem solar cell based on tunnel oxide passivated contacts (TOPCon) tech for the bottom cell.

“We fabricate the perovskite sub-cell conformally on the damage-etched front surface to mitigate the negative impacts of rough c-Si substrates, thus preventing shunt paths across carrier transport layers, absorber layers, and their interfaces in relevance,” the scientists said, noting that they followed a standard wafering and etching process that is commonly used in the PV industry.

University of Surrey researchers have produced solar cell building blocks out of perovskite ink. Current inks do not guarantee seamless transitions on an industrial scale, as the manufacturing process needs to be highly controlled and optimized. That is why the team developed a perovskite ink that presents a fast and reproducible way to fabricate these solar cell building blocks on a mass scale. 

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.”

Researchers from Wuhan University and Shenzhen University in China have designed a four-junction tandem (4T) solar cell based on perovskite and copper, indium, gallium and selenium (CIGS), through a novel surface passivation technique that uses guanidine bromide (GABr).

The team tested GABr in mixed solvents combining isopropyl alcohol (IPA) and toluene (TL), which they said can efficiently passivate interface and grain boundary defects by minimizing the IPA solubility of the perovskite surface. They compared the mixing of IPA with ethyl acetate (EA), chlorobenzene (CB), and toluene (TL) to dissolve GABr, and further optimized the concentration of GABr and the mixing ratio of the two solvents.

Researchers from the University of Nebraska-Lincoln and the University of California, Berkeley, have used perovskite materials to develop a new photonic device that could get scientists closer to the “holy grail” of finding the global minimum of mathematical formulations at room temperature. Finding that illusive mathematical value would be a major advancement in opening new options for simulations involving quantum materials.

Many scientific questions depend heavily on being able to find that mathematical value, said Wei Bao, Nebraska assistant professor of electrical and computer engineering. The search can be challenging even for modern computers, especially when the dimensions of the parameters — commonly used in quantum physics — are extremely large. Until now, researchers could only do this with polariton optimization devices at extremely low temperatures, close to about minus 270 degrees Celsius. Bao said the Nebraska-UC Berkeley team “has found a way to combine the advantages of light and matter at room temperature suitable for this great optimization challenge.”

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. 

Researchers at Florida State University (FSU), in collaboration with ones from Argonne National Laboratory, have examined what happens when a halide perovskite faces real-world conditions, as opposed to pristine conditions of a chemistry lab.

They found that stressing halide perovskites with light and electric fields can create changes in the basic properties of the material and distort the lattice structure that is crucial to keeping this material stable.

Researchers from The Australian National University, Flinders University, University of New South Wales and The University of Sydney have developed a perovskite solar cell with a novel passivation process based on the use of guanidinium (Gua) and octylammonium (Oa) spacer cations.

 A schematic showing the device structure and the surface incorporation of GuaBr, OABr, and their mixture. Image from RL Solar

The team claims that guanidinium salts can improve the performance of the perovskite film, as guanidinium ions are capable of penetrating into the bulk of the perovskite material and localizing at the grain boundaries (GBs).