Peter Trefonas

Double-heterojunction nanorod light-responsive LEDs for display applications

Multifunctional displays As we head toward the “Internet of things” in which everything is integrated and connected, we need to develop the multifunctional technology that will make this happen. Oh et al. developed a quantum dot-based device that can harvest and generate light and process information. Their design is based on a double-heterojunction nanorod structure that, when appropriately biased, can function as a light-emitting diode or a photodetector. Such a dual-function device should contribute to the development of intelligent displays for networks of autonomous sensors. Science, this issue p. 616 A dual-function device capable of light harvesting and emission is demonstrated for intelligent displays. Dual-functioning displays, which can simultaneously transmit and receive information and energy through visible light, would enable enhanced user interfaces and device-to-device interactivity. We demonstrate that double heterojunctions designed into colloidal semiconductor nanorods allow both efficient photocurrent generation through a photovoltaic response and electroluminescence within a single device. These dual-functioning, all-solution-processed double-heterojunction nanorod light-responsive light-emitting diodes open feasible routes to a variety of advanced applications, from touchless interactive screens to energy harvesting and scavenging displays and massively parallel display-to-display data communication.

Multilayer Transfer Printing for Pixelated, Multicolor Quantum Dot Light-Emitting Diodes

Here, we report multilayer stacking of films of quantum dots (QDs) for the purpose of tailoring the energy band alignment between charge transport layers and light emitting layers of different color in quantum dot light-emitting diodes (QD LED) for maximum efficiency in full color operation. The performance of QD LEDs formed by transfer printing compares favorably to that of conventional devices fabricated by spin-casting. Results indicate that zinc oxide (ZnO) and titanium dioxide (TiO2) can serve effectively as electron transport layers (ETLs) for red and green/blue QD LEDs, respectively. Optimized selections for each QD layer can be assembled at high yields by transfer printing with sacrificial fluoropolymer thin films to provide low energy surfaces for release, thereby allowing shared common layers for hole injection (HIL) and hole transport (HTL), along with customized ETLs. This strategy allows cointegration of devices with heterogeneous energy band diagrams, in a parallelized scheme that offers potential for high throughput and practical use.

Region specific enhancement of quantum dot emission using interleaved two-dimensional photonic crystals

We demonstrate an approach in which visible-wavelength-emitting quantum dots (QDs) are integrated within a polymer-based photonic crystal (PC) and excited by an ultraviolet-emitting LED. The PC design incorporates two interleaved regions, each with distinct periods in orthogonal directions to enable simultaneous resonant coupling of ultraviolet excitation photons to the QDs and visible QD emission at two different wavelengths to efficiently extract photons normal to the PC surface. The combined excitation and extraction enhancements result in a 5.8X increase in the QD output intensity. Further, we demonstrate multiple QD-doped PCs combined on a single surface to optimally couple with distinct populations of QDs, offering a means for blending color output and directionality of multiple wavelengths.