Researchers have created a high-performance hybrid LED (light emitting diode), comprised of both organic and QD-based (Quantum dot) layers. Until recently, however, engineers have been vexed by a manufacturing problem that hindered commercial development. An industrial process known as vacuum deposition is the common way to put the necessary organic molecules in place to carry electricity into the QDs. However, a different manufacturing process called spin-coating, is used to create a very thin layer of QDs. Having to use two separate processes slows down production and drives up manufacturing costs.
Multilayer, colloidal quantum-dot based light-emitting diodes that exhibit high brightness, solution processability, colour tunability and narrow emission bandwidth are reported. These devices consist of a quantum-dot emissive layer sandwiched between an organic hole transport layer and an electron transport layer of ZnO nanoparticles, all of which are deposited using a solution process. The devices have maximum luminance and power efficiency values of 4,200 cd m^−2 and 0.17 lm W^−1 for blue emission, 68,000 cd m^−2 and 8.2 lm W^−1 for green, and 31,000 cd m^−2 and 3.8 lm W^−1 for orange-red. Moreover, with the incorporation of the ZnO nanoparticles, these devices exhibit high environmental stability, and the unencapsulated devices have operating lifetimes exceeding 250 h in low vacuum with an initial brightness of 600 cd m^−2.
According to the Nature Photonics article, UF researchers overcame this obstacle with a patented device structure that allows for depositing all the particles and molecules needed onto the LED entirely with spin-coating. Such a device structure also yields significantly improved device efficiency and lifetime compared to previously reported QD-based LED devices.
Spin-coating may not be the final manufacturing solution, however.
“In terms of actual product manufacturing, there are many other high through-put, continuous “roll-to-roll” printing or coating processes that we could use to fabricate large area displays or lighting devices,” Xue said. “That will remain as a future research and development topic for the university and a start-up company, NanoPhotonica, that has licensed the technology and is in the midst of a technology development program to capitalize on the manufacturing breakthrough.”