Double Heterojunction Nanorods: From Light-Emitting Diodes to Advanced Display Concepts

P. Trefonas III, B.H. Kim, V. Kumar, S. Nam, M.S. Naughton, N. Oh, Y. Zhai, P.J.A. Kenis, J.A. Rogers, M. Shim, K. Deshpande, T. Ewers, K. Howard, J. Park, J. Zhang
Dow Chemical Company,
United States

Keywords: nanorods, LED

Summary:

Consumers are demanding ever increasing performance from electronic displays, including energy efficiency, brightness, color gamut, multifunctional user interfaces, lightweight thin design and reasonable cost economics. Many of these individual features have been demonstrated in single function devices, but combining them together often leads to undesirable performance and cost compromises. Integrating all of these features simultaneously with a simple materials design is a considerable challenge in materials sciences. Colloidal quantum dot (QD) light emitting diode (LED) displays readily lend themselves to an all-solution process design for the charge transporting and emitting layers. This simplicity should give a significant cost advantage over organic-LEDs (OLED) displays, which perform best when built using complex serial evaporative deposition steps. Advances in QD-LED have led to efficiencies and brightness rivaling evaporative those of OLED displays, however the spherical shape of core-shell QDs can place apparent upper limits on internal quantum efficiency (IQE) due to the light outcoupling issues. Here we discuss novel double-heterojunction nanorod (DHNR) LEDs which due to the shape anistropy and the propensity to assembly in an ideal planar alignment when deposited in a solution process. Moreover the ability to design near optimal band offsets assists in facile charge transport of both holes and electrons, with minimal interfacial resistance, giving excellent charge balance characteristics. We have demonstrated very low threshold voltage with high brightness (75,000 cd m-2) and efficiencies (EQE = 12%, current efficiency = 27.5 cd A-1, and power efficiency = 34.6 lm W-1). We will also describe the synthesis of nanocrystals in a continuous feed microreactor system, yielding a substantial material output with high consistency and lowered manufacturing costs. Aspects of the continuous flow feed design and results with the system will be discussed. One application we will highlight will be the development of highly novel display devices based upon semiconductor nanocrystal quantum dots and DHNRs which allow for novel electronic functionality that enhances the ability of the device to interface with external stimuli. These new display devices should allow for unique interfaces and interactivity with users leading to new functionality that could have commercial application in the design of future electronic devices for consumer and data markets. 1. Double-Heterojunction Nanorods, Nature Communications 5 3642 (2014) 2. High efficiency and optical anisotropy in double-heterojunction nanorod light-emitting diodes, ACS Nano 9 878 (2015) 3. High temperature flow synthesis of CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS nanocrystals, Nanoscale, 7, 15895 (2015).