Technical / research - Page 57

An international team of researchers recently tested a new way of passivating defects in perovskite solar cells. Using a tailored arrangement of atoms, the team managed to overcome challenges related to the formation of a two-dimensional perovskite layer on top of the active cell material, and reach 21.4% conversion efficiency for a 26cm² active area, which is said to be a record for a perovskite device of this size.

Passivation layers, deposited on top of the perovskite material, play an essential role in reducing material defects and unwanted reactions within the material, to improve both performance and stability. One strategy that has been found effective is the use of alkylammonium halides. In many cases these form an additional two-dimensional perovskite layer on top of the perovskite, which can improve device stability but also negatively affect performance.

Researchers from University of North Carolina, North Carolina State University and Chinese Academy of Sciences have fabricated a mini perovskite solar module using a novel encapsulation technique based on the use of a self-healable, lead-adsorbing ionogel that prevents lead leakage and improves stability. The solar module has an area of 31.5cm² and has a reported efficiency of 22.9%.

Ionogel microstructure and lead adsorption mechanism. Image from article

The scientists explained that ionogel sealants were applied on the panel's front glass and between electrode and encapsulation glass, with the 100μm-thick inonogel being able to hold the shattered glass together even if the glass breaks. This is claimed to effectively suppress lead leakage from broken modules after hail test or compression by car wheels, and soaking in water for 45 days.

Scientists in Germany's Karlsruhe Institute of Technology (KIT) have applied vapor-based deposition techniques and laser scribed interconnection (well established processes in existing thin-film solar manufacturing) to fabricate perovskite mini modules which achieved a maximum efficiency of 18% for a device measuring 4cm².

The team believes that based on these processes, it would be possible to simplify processing and reduce losses associated with scaling up to commercial-sized devices.

A research team, led by Germany's Fraunhofer Institute for Solar Energy Systems (ISE), studied two stages of cell manufacturing that are among the most in need of optimization due to growing concerns over the availability of the commonly used indium and silver: transparent conductive oxide deposition and cell metallization.

The research takes processes used in silicon heterojunction (HJT) cell manufacturing as a starting point, and examines how the addition of a perovskite top cell would change the requirements for the rest of the cell structure.

Scientists at the National Renewable Energy Laboratory (NREL) and Northern Illinois University (NIU) have developed a way to prevent lead from escaping damaged perovskite solar cells. This could go a long way in addressing concerns about potential lead toxicity.

Image by NREL, from Phys.org

The light-absorbing layer in perovskite solar cells contains a small amount of lead. Simply encapsulating solar cells does not stop lead from leaking if the device is damaged. Instead, chemical absorption may hold the key. The researchers report being able to capture more than 99.9% of the leakage.

A research team at KTH Royal Institute of Technology has developed a synthetic alloy that increases perovskite cells' durability while preserving energy conversion performance.

'Perovskite usually dissolves immediately on contact with water,' says co-author James Gardner, a researcher at KTH. 'We have proven that our alloyed perovskite can survive for several minutes completely immersed in water, which is over a 100 times more stable than the perovskite alone. What's more, the solar cells that we have built from the material retain their efficiency for more than 100 days after they are manufactured.'

A research team from the Fraunhofer Institute for Solar Energy Systems, NREL, Solaronix SA and the Materials Research Center of the University of Freiburg has reported perovskite solar cells with carbon-based electrodes, which demonstrate impressive resilience against reverse-bias-induced degradation.

Previous studies have shown that a negative voltage applied to conventional perovskite solar cell stacks resulted in breakdown and irreversible destruction of the device. In this study, the international research team identified two main degradation mechanisms. The first is iodine loss due to hole tunneling into perovskite, which takes place even at low reverse-bias but decomposes the perovskite only after long time durations. Another factor is local heating at large reverse-bias leading to the formation of PbI₂, which starts at shunts and then follows the path of the least resistance for the cell current, which is primarily influenced by the electrode sheet resistance. The newly designed modules successfully endured the hotspot test conditions specified in IEC 61215-2:2016 international standard at an accredited module testing laboratory.

Researchers at South Korea's Ulsan National Institute of Science and Technology (UNIST) and Pohang University of Science and Technology report a power conversion efficiency of 25.8% for a single junction perovskite solar cell, by forming a coherent interlayer between electron-transporting and perovskite layers to reduce interfacial defects.

The cell was built with an interlayer between a tin(IV) oxide (SnO₂) electron-transporting layer and a layer made of a halide perovskite layer by coupling chlorine-bonded SnO₂ with a perovskite precursor containing chlorine. 'This interlayer has atomically coherent features which enhance charge extraction and transport from the perovskite layer; and fewer interfacial defects,' the academics explained.

Researchers from Florida State University and Washington University in St. Louis have developed a new material for displays and a novel way to fabricate it'using an inkjet printer. The team used organometal halide perovskites ' with a novel twist.

The traditional way to create a thin layer of perovskites, which is in liquid form, is to drip it onto a flat, spinning substrate, in a process known as spin coating. As the substrate spins, the liquid spreads out, eventually covering it in a thin layer. From there, it can be recovered and made into perovskite LEDs, or PeLEDs. A lot of material, however, is wasted in that process'as the substrate spins at several thousand RPM, some of the dripping perovskite splatters and flies away, not sticking to the substrate. The researchers substituted this process with one based on an inkjet printer.

A recent study by Lawrence Berkeley National Laboratory (Berkeley Lab), Technische Universität München, EPFL and The Pennsylvania State University has found that solar materials manufacturing could be aided by a new instrument that uses two types of light ' invisible X-ray light and visible laser light ' to probe a perovskite material's crystal structure and optical properties as it is synthesized.

'When people make solar thin films, they typically have a dedicated synthesis lab and need to go to another lab to characterize it. With our development, you can fully synthesize and characterize a material at the same time, at the same place', said Carolin Sutter-Fella, a scientist at Berkeley Lab's Molecular Foundry.