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Thin Films: A Step Closer to Solar-Cell Windows
Posted on November 17th, 2017 by Chris Walker in Chemical Manufacturing Excellence
Thin films crop up all over the place in our daily lives. They appear as the antireflection coatings on our glasses, on CDs and DVDs, on magnetic tapes and in lasers. Life wouldn’t be the same without them. It’s semiconductor thin films, and the ability to grow them uniformly, that are behind the modern advances in transistor technology. These are the thin films responsible for you being able to read this article on a tiny computer in your palm.
Another set of materials we can’t escape from are oxides, oxygen-rich compounds used to make glass, ceramics, chalk and a whole host of other useful objects.
Where these two meet, things start to get exciting. Thin films of oxides are predicted to be as revolutionary as those made of semiconductors. This is where the future lies. The problem so far is that these films are extremely hard to grow in a controlled manner free from defects.
However, recently a team of researchers from the USA and Singapore have succeeded in growing thin films of a class of oxides known as perovskites, with minimal defect concentration and a high conductivity. These high-quality oxide films might just be the start of a revolution in the kind of materials we use to build modern electronics.
Thin Film Applications
Physicists and materials scientists have long been convinced that even the most familiar oxides can show surprisingly useful properties if formed in the right structures. Heterostructures, which are cake-like layers of thin films stacked on top of one another where each film is only about a few atoms thick, are what everyone is trying to reliably fabricate.
These versatile films (if the dimensions and growth parameters are just right) can exhibit properties such as interface superconductivity and magnetism, and are tuneable by applying voltages.
These phenomena are largely due to the oxygen present in these materials, which tends to draw electrons away from other atoms, leading to a local electric field in which the electrons can move and carry current. This can make the film conductive at the interface even when the film layers themselves are totally insulating. Such a film could be of great use for applications like solar cells, magnetic sensors and memory, as well perhaps leading to the engineering holy grail of room-temperature superconductivity.
The key to making oxide thin films with such a mobile electron layer is to create an atomically clean interface, which has no defects to scatter the electrons and reduce the ballistic nature of their movement. This is difficult because oxides often have complex crystal structures, and the film will not grow properly unless the right atoms are exposed on the top surface for making the correct chemical bond.
High-Conductivity Oxide Breakthrough
And so, the recent breakthrough in oxide thin film growth is so welcome. The perovskite thin films grown by the research team show great promise as transparent conductors. They have the potential to be used as electrodes in a solar cell, retaining transparency so sunlight can pass through them when placed on a large window or a display screen.
With the sheer volume of glass used in modern architecture, the opportunity in turning all of these surfaces into solar energy convertors is clearly huge.
Oxide heterostructures look like they’re here to stay, whether as a new class of electronics altogether, or as solar cells ushering a new era of energy generation. Either way, this marks another step forward into making their everyday use viable.
All opinions shared in this post are the author’s own.
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