OLEDs: Beware of Falling Prices
As you'll come to discover, one of the big topics we'll address on this blog is the cost of OLED technology; mainly, why it's currently so high and what innovators like ourselves are doing about it. We were alerted to yet another fantastic explanation on the "how" of OLED cost reduction, courtesy of @Mersive on Twitter. Be sure to read the entire article, but first, check out this interesting excerpt:
Most of my readers are familiar, at a high level, with the advantages of OLED – each element in an OLED emits it own light that can be switched on and off. This means better black levels, bright spatially localized color, and manufacturing advantages when you don’t have to include a backlight technology like LCD requires. For example, OLED can be built into curved displays.
However, the requirement for rare metals has kept costs high. Why the need for the metals? It turns out that my description of atomic emission is not yet complete. In order to decide if an atom will release a photon when the electron falls into place, the quantum spin of both the electron and the “hole” need to be taken into account. Spin is an atomic property that, at a marco level, gives rise to magnetism and, similarly, governs how very small things, like electrons, interact. Because an electron has two possible spin states, there are four possible spin combinations between an electron and the corresponding “hole” it falls into. Only one of these combinations will emit a photon, while the other three emits energy in the form of heat. Yes, you heard me right, left unchecked, your OLED TV would only transfer 1/4th of its energy into light and the rest would just warm your living room. In order to avoid this problem, the carbon molecules are combined with the hydrocarbon molecules to modify the spin states of the holes. Creating a statistically greater mix of states that will generate light. Very clever – but expensive.
The new research I mentioned is exciting in that it makes use of the fact that, if an electrically excited state is left that way long enough, the spin state will flip into a state that will always emit a photon. So, if a hole can be created but not filled for a few milliseconds, it is almost always going to be found in the correct (more energy efficient) spin state. This sounds like a short amount of time, but keep in mind that it typically takes on the order of nanoseconds for an electron to find and fall into an electron whole. The new approach under development, then focuses on ways to stall this process. The technique that they report in a paper in Angewandte Chemie uses peculiarly shaped organic molecules that are able to trap the free electron long enough that the spin state of the hole will have flipped prior to absorption. It’s very clever, and has great promise.
Head spinning? If you're not interested in the mechanics, just know that affordable OLED products on their way soon. Very soon.