That's a Stretch

To date, flexible displays have, by and large, proven to be more hype than reality. Sure, there are a number of flexible displays on the market, but they come with limitations related to display quality, expense, and wear and tear that have kept them from widespread adoption. These problems stem from current methods used to manufacture LEDs.

Both organic and inorganic LEDs are commonly used in displays, with each bringing its own set of tradeoffs. Organic LEDs are inexpensive and flexible, however, they have a short life span, and do not perform especially well. Inorganic LEDs, on the other hand, perform very well, but are expensive and inflexible. By themselves, neither option is particularly well suited for the development of flexible displays.

A team from Washington University in St. Louis found a way to get the best of both worlds, by creating LEDs that are organic-inorganic hybrids. They did this by embedding stiff, inorganic perovskite crystals into an organic, stretchable polymer matrix. The perovskite crystals can be used to make perovskite LEDs, which are made flexible by the substrate that they are deposited on.

To make the LEDs functional, it was necessary to create a sandwich of materials. In addition to the perovskite layer, a pair of electrode layers, as well as a buffer layer, were incorporated into the design. This was a bit tricky to pull off successfully, because the perovskite layer must not be allowed to mix with the adjacent layers. With much experimentation, the researchers were able to find a material to fill this requirement, by siting between the perovskite and other layers, that offered the optimal mix of performance and protection.

Not content to just develop novel, stretchable LEDs, the team also designed a more efficient manufacturing process for their production. Layers of perovskite are traditionally manufactured by dripping liquid perovskite onto a spinning substrate. As it spins, the perovskite spreads out and covers the entire surface in a thin layer. Creating a sheet of perovskite in this way can take upwards of five hours.

Given that the perovskite is in a liquid form during application, the researchers thought to use an inkjet printer to apply it to surfaces. Not only does this process modification allow for precision allocation of the perovskite, but it also reduces fabrication time to less than 25 minutes. A further benefit of the technique is that it can apply material to substrates that may become unstable while spinning, such as rubber, which increases the areas for application of the technology.

The researchers believe that their contribution could be the first step in an electronics revolution. They envision a whole new class of wearable devices and interactive environments being enabled. Only time will tell if these dreams are able to pan out in the real world.