Researchers have achieved a new level of control over the atomic structure of a family of materials known as halide perovskites, creating a finely tuned ‘energy sandwich’ that could transform how solar cells, LEDs and lasers are made.
Due to their remarkable ability to absorb and emit light, and because they are cheaper and can be configured to convert more of the solar spectrum into energy than silicon, perovskites have long been touted as a potential replacement for silicon in solar cells, LEDs and quantum technologies.
However, their instability and durability have, so far, largely limited perovskite devices to the laboratory. In addition, scientists have struggled to precisely control the thickness of perovskite films, and control how different perovskite layers interact when stacked together – an important step in building functional, multi-layered structures.
Now, a team of researchers led by the University of Cambridge has found a new way to grow ultra-thin layers of perovskite films so their atoms line up perfectly, which could enable more powerful, durable and efficient devices.
“We’ve reached a level of tunability that wasn’t even on our radar when we started,” said St John’s College Fellow Professor Sir Richard Friend from the Cavendish Laboratory, who co-led the research.
The researchers used a vapour-based technique to grow three-dimensional and two-dimensional perovskites one layer at a time, which enabled them to control the thicknesses of the films down to fractions of an atom. Their results, reported in the journal Science, could open the door to usable perovskite devices that can be produced at scale, using a process like that used to make commercial semiconductors.
Each layer in a semiconductor ‘sandwich’ does a different job in moving electrons and their positively-charged counterparts – called holes – around and determines how the semiconductors absorb or emit light. Together, the layers act like one-way streets that guide the electric charges in opposite directions, preventing them from bumping back into each other and wasting energy as heat.
In other widely used semiconductors, such as silicon or newer materials such as gallium nitride, the properties of the individual layers can be fine-tuned using various methods. But perovskites, despite their excellent performance, have so far proved difficult to control in layered devices, due in part to their ‘chaotic’ atomic structure.
“A lot of perovskite research uses solution processing, which is messy and hard to control,” said Professor Sam Stranks from the Department of Chemical Engineering and Biotechnology, who co-led the research. “By switching to vapour processing – the same method used for standard semiconductors – we can get that same degree of atomic control, but with materials that are much more forgiving.”
The researchers also found they could engineer the junctions between the layers to control whether electrons and holes stayed together or apart – a key factor in how efficiently a material emits light.
Sir Richard said: “We can now decide what kind of junction we want – one that holds charges together or one that pulls them apart – just by slightly changing the growth conditions.”
