Functional Film with Electric‐Field‐Aided Aligned Assembly of Quantum Rods for Potential Application in Liquid Crystal Display

Abstract

conquered the large-area display market owing to its advantages such as higher resolution and longer lifetime, but faced challenges from OLED devices in terms of module thickness, response time, and vivid colors. [1] The traditional LCD technology uses blue light-emitting diodes (LEDs) coupled with a yellow phosphor to originate a white light which is transmitted through an assembly of devices comprising polarizers, thin-film transistor array, liquid crystals, and color filters. [2] However, the wide transmission through the color filters and broad emission spectrum of yellow phosphor practically inhibits the realization of wider color gamut in such LCD devices. [3] Semiconductor quantum rods (QRs), owing to their higher brightness, [4] color purity, [5] and polarized light emission [6] features, are lending prominent prospects for their application in display technology. The use of quantum dots in the backlight unit in the form of quantum-dot enhancement film has already been demonstrated [7] ; however, the emission from these spherical particles is isotropic. A unidirectional aligned array of QRs coupled with LCD backlight can be foreseen as a viable option to attain wider color gamut and light polarization. [8] A polarized blue light coming from either laminated conventional polarizer or in-cell coated polarizer can stimulate the QRs to provide narrow red and green polarized emission (Figure 1). This can result in reduced color crosstalk, and hence LCD with high color gamut and contrast ratio can be realized.The alignment of QRs is crucial to attain maximum polarized light emission. Several approaches have been demonstrated in the past on this pathway such as by utilizing photoalignment technology, [9] mechanical rubbing, [10] assembly in liquid crystal defects, [11] and solvent evaporation-assisted assembly. [12] Furthermore, QRs embedded in nanofibers sheets using electrospinning [13] and mechanical stretching of polymer film [14] have been reported with higher degree of alignment. The use of external electric field has been well known to arrange QRs as both parallel [15,16] and perpendicular [17] to the substrate. Herein, we report a simplistic approach for unidirectional alignment of CdSe/CdS QRs by utilizing external electric field after mixing in solvent-based reactive mesogen (RM). The QRs showed higher Harnessing the unique polarized light emission characteristic from semiconductor quantum rods (QRs) necessitates their large-area unidirectional alignment. Herein, the aligned assembly of CdSe/CdS QRs is demonstrated by fabricating a functional film on a micrometer-spaced interdigitated electrodes substrate over an area of ≈1.3 cm 2 . The external electric field is used to control the position and orientation of QRs which is later frozen by the polymerization of reactive mesogen under the exposure of UV light.Under the fluorescence microscope, a judicious change in the QRs emission intensity with the polarizer axis positioned parallel and perpendicular to the alignment direction suggests the optica...

Ordered polymer composite materials: challenges and opportunities

“…Furthermore, the well-ordered nanomaterial arrays can be further utilized as a template to regulate the alignment of other small molecules within the composite network in such a way that the properties of the small molecules (e.g., absorption and emission bands) can be controlled ( Figure 1c). 41 Applied electric fields 14,[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] have also been used to control the organization of nanocomponents with permanent or induced dipole moments by means of dielectrophoretic forces (DEP), 14,63,64,65 where the structure of the assembled nanocomponents can be manipulated by varying electrode geometry to create non-homogenous electric fields. As with magnetic field assembly, in-situ polymerization is usually carried out after forming ordered nanofiller structures to fix their positions within the polymer matrix ( Figure 2).…”

Efficient and Stable CdSe/CdS/ZnS Quantum Rods-in-Matrix Assembly for White LED Application

“…For this reason, the WLED application demands a narrow emitting phosphor in the red-light region. On the other hand, the display application also demands a narrow red emission peak to ensure high color purity and wide color gamut [13,23]. Commercial silicate or nitride-based red phosphors possess a broad emission peak that limits lighting and display applications.…”

“…This heterostructure endows the CdSe/CdS quantum rods (QRs) with a larger Stokes shift, intense polarized emission, faster radiative decay, and intrinsic charge separation [5][6][7][8]. These unique optical and electrical features make CdSe/CdS QRs promising for optoelectronic applications such as light-harvesting [7], biosensing [4], visible lighting communication [9][10][11], and light-emitting diodes (LEDs) [12,13]. Conventional CdSe/CdS QDs present a large overlap between the absorption and emission spectra that induces strong concentration quenching of QDs and a thermal issue in optoelectronic devices [14][15][16][17][18].…”

Multi‐Dimensional Quantum Nanostructures with Polarization Properties for Display Applications

“…In this regard, several strategies have been developed in the last decade . With the assistance of an external electric field, nanorods could self‐assemble along the direction of the field lines and got the polarization ratios of 0.48 . However, to align large areas, much higher electric fields were needed.…”