The week in perovskites

Academics led by researchers at Russia’s Far Eastern Federal University have demonstrated a laser process for etching nanostructures onto a perovskite layer, taking advantage of the material’s poor thermal conductivity and potentially overcoming challenges arising from the material’s tendency to suffer damage during processing.

The group used femtosecond laser pulses to scribe nanostructures onto a layer of methylammonium lead iodide. Their experiments with the laser process are described in the paper Light-Emitting Nanophotonic Designs Enabled by Ultrafast Laser Processing of Halide Perovskites, published in the journal Small. The group created ordered nanoholes and strips as narrow as 250 nanometers, as well as nanowire lasers as thin as 500 nanometers.

The perovskite’s poor thermal conductivity was crucial as it prevented heat generated by the laser from spreading further into the material, allowing for the scribing of precise patterns. “It is very difficult to nanostructurize conventional semiconductors such as gallium arsenide using a powerful pulsed laser,” said Sergey Makarov, a leading researcher at the faculty of physics and engineering at the ITMO University in St Petersburg. “The heat is scattered in all directions and all the thin, sharp edges are simply distorted by this heat. It’s like if you try to make a miniature tattoo with fine details but, due to the paint spreading out under the skin, you will just get an ugly blue spot.”

The group also found laser processing could be used to change the color of the perovskite without adding materials, potentially allowing for solar cells to be produced in different colors.

Cutting out lead

As perovskites move closer to commercial production, the question of their reliance on toxic lead is often raised. In the perovskite crystal structure, lead can easily be replaced with other metals. However, lead-free perovskites have thus far lagged when it comes to solar cell performance.

Researchers at the University of Groningen in the Netherlands have been working with tin-based perovskite formamidinium tin iodide (FaSnI₃). Previous work confirmed mixing FaSnI₃ crystals with fellow organic material phenylethylammonium (PEA) increased the stability of the material but reduced its photovoltaic efficiency.

A separate group at Groningen headed to the European Synchrotron Facility in Grenoble, France, and used x-rays to observe the formation of the perovskite film in a spin coating process. Their results were published in the paper Mechanism of Crystal Formation in Ruddlesden–Popper Sn‐Based Perovskites, in Advanced Functional Materials.

The Groningen team discovered the PEA additive formed an insulating layer which dramatically reduced solar cell performance when the additive was used in higher concentrations. The group concluded, avoiding the formation of such a layer was key to fabricating a stable tin-based perovskite and the researchers plan to investigate further tweaks to the additive process which could allow for higher concentrations of PEA without reducing efficiency.

Flexible perovskite modules

Polish tech company Saule has received €4.35 million from the country’s National Center for Research and Development to mass-produce flexible perovskite solar modules for internet-of-things applications. “Successfully finishing our first project with the launch of our pilot line has shown that we have an excellent team and technology,” said Saule chief technology officer Olga Malinkiewicz. “With this opportunity we are lunging towards the mass production of our devices.” Saule Technologies has been working on an inkjet printing process for the production of flexible perovskite solar modules since 2014. With the technology, the shape, color and size of modules could be adapted to customer requirements. The modules are stable and water resistant, Saule claims, and could be installed anywhere on a building envelope.

Oxide-ion conductivity

Scientists from the Tokyo Institute of Technology have discovered a layered perovskite which shows unusually high oxide-ion conductivity. Oxide-ion conductors built with the material could be used in fuel cells to convert clean fuel such as hydrogen into electrical energy, or in oxygen separation membranes which could be used for CO₂ capture.

Blue light

Researchers at Florida State University claim to have created a hollow nanostructure for metal-halide perovskites that would allow the material to emit a highly efficient blue light. The scientists used a metal-halide perovskite that exhibited pronounced quantum size effects. The new technology is said to offer strong potential for photon-related technologies such as light-emitting diodes and lasers.