No abstract

Since the discovery of carbon nanotubes, researchers have been fascinated by their mechanical and electrical properties, as well as their versatility for a wide array of applications. In this study, a carbon nanotube-polyelectrolyte composite multilayer thin film fabricated by a layer-by-layer (LbL) method is proposed to develop a multifunctional material for measuring strain and corrosion processes. LbL fabrication of carbon nanotube composites yields mechanically strong thin films in which multiple sensing transduction mechanisms can be encoded. For example, judicious selection of carbon nanotube concentrations and polyelectrolyte matrices can yield thin films that exhibit changes in their electrical properties to strain and pH. In this study, experimental results suggest a consistent trend between carbon nanotube concentrations and strain sensor sensitivity. Furthermore, by simply altering the type of polyelectrolyte used, pH sensors of high sensitivity can be developed to potentially monitor environmental factors suggesting corrosion of metallic structural materials (e.g. steel, aluminum).

An ultrathin skin-attachable display is a critical component for an information output port in next-generation wearable electronics. In this regard, quantum dot (QD) light-emitting diodes (QLEDs) offer unique and attractive characteristics for future displays, including high color purity with narrow bandwidths, high electroluminescence (EL) brightness at low operating voltages, and easy processability. Here, ultrathin QLED displays that utilize a passive matrix to address individual pixels are reported. The ultrathin thickness (≈5.5 µm) of the QLED display enables its conformal contact with the wearer's skin and prevents its failure under vigorous mechanical deformation. QDs with relatively thick shells are employed to improve EL characteristics (brightness up to 44 719 cd m at 9 V, which is the record highest among wearable LEDs reported to date) by suppressing the nonradiative recombination. Various patterns, including letters, numbers, and symbols can be successfully visualized on the skin-mounted QLED display. Furthermore, the combination of the ultrathin QLED display with flexible driving circuits and wearable sensors results in a fully integrated QLED display that can directly show sensor data.

Transparent displays lie at the heart of next generation optoelectronics [1,2] in the era of augmented reality (AR), wearable electronics, and internet of things (IoTs). [3][4][5][6][7] Being transparent for light-emitting diodes (LEDs) significantly expands their applications by displaying visual information on objects without affecting their original appearance and functionality. However, there has been a large gap in the electroluminescence (EL) performance between transparent displays and nontransparent counterparts, [8] due in large part to imbalanced injection of charge carriers into the emitter, unoptimized energy band alignment of the top electrode, and vulnerability of organic and/or polymeric light emitting materials during the deposition of transparent conducting oxide electrodes. [9][10][11][12] The previous progresses and unmet requirements for transparent displays are described in Section S2.1, Figure S1, and Table S1 of the Supporting Information. In addition, there has been much need to develop novel device architectures [13][14][15][16] that consider the carrier dynamics for high-performance transparent quantum dot light-emitting diodes (Tr-QLEDs).For high-quality transparent displays, first of all, high transparency is an absolute requirement. [17] The effect of transparency on visibility of background is examined on the university logo and a leaf (Figure 1a). For transparency below 70% (semitransparency), the color and contrast of objects behind the display are significantly deteriorated. In contrast, Tr-QLEDs of 84% transparency present clear background view in both cases. Secondly, high brightness and color purity are particularly important for vividness of "see-through" displays. The maximum brightness of conventional displays (e.g., smart phones and monitors) is around 600 cd m −2 . For see-through displays, however, the displayed information becomes blurred at this brightness (i.e., 600 cd m −2 ) because of photointerference with ambient light (Figure 1b; Figure S2a, Supporting Information). Therefore, significantly higher brightness is required to ensure clear and vivid displays (Figure 1b). In addition, chromatic aberrations can be minimized by employing engineered quantum dots (QD) emitters [18,19] that exhibit better color purity than organic and/or polymer emitters ( Figure S2b, Supporting Information). Lastly, integration of highly deformable Displaying information on transparent screens offers new opportunities in next-generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such "see-through" displays to show vivid images over clear background view. Here transparent quantum dot light-emitting diodes (Tr-QLEDs) are reported with high brightness (bottom: ≈43 000 cd m −2 , top: ≈30 000 cd m −2 , total: ≈73 000 cd m −2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplishe...