Cellulose Nanocrystal:Polymer Hybrid Optical Diffusers for Index‐Matching‐Free Light Management in Optoelectronic Devices

Abstract

exploited for the purpose of uniform backlighting, brightness enhancement, efficiency improvement, and increased sensitivity in liquid crystal displays (LCDs), [1][2][3] light-emitting diodes (LEDs), [4][5][6] solar cells, [7][8][9] and photodetectors, [10][11][12] all via excellent light scattering properties of optical diffusers.As a nontoxic and biodegradable material, cellulose nanocrystals (CNCs) are environment friendly. They are directly extracted from natural resources such as wood and other fiber supplies available in plants. As a high-molecular-weight linear polymer formed of monomers linked together by glycosidic oxygen bridges, [13] they offer desirable bulk and nanoscale properties (e.g., high tensile strength, high surface area for interaction with surrounding species) [14] that make them suited for use as substrates in devices such as sensors, [15] solar cells, [16] LEDs, [17] and transistors. [18] In addition, recently, cellulose nanofiber (CNF)-based films and papers have attracted attention for their light scattering capabilities. [9,19,20] Both CNCs and CNFs are very similar in terms of chemical composition and can be derived from the same source but are morphologically different in that CNFs are long (in order of micrometers) and flexible composed of both crystalline and amorphous parts while CNCs are short rod-like crystals with lengths in the range of a few hundreds of nanometers. [21] Here, we propose, fabricate, and characterize a new class of optical diffusers based on CNP hybrid films. While some of the recently proposed volumetric diffusers are made of rare earth materials such as cerium [22] which can drive up the cost of fabrication, the proposed diffuser relies on a ubiquitous and environment-friendly material, cellulose, which is cost-effective to produce. Our hybrid diffuser achieves high haze values (up to 85%), which is significantly higher than cellulose nanofiber/ wood pulp diffusers, [9,20] while maintaining a high degree of transparency (≈85%). In addition, unlike previously reported cellulose nanofiber/wood pulp optical diffusers which require an additional index-matching layer between the diffuser and the device for efficient light coupling, [9,20] no index-matching is required for the diffuser here due to the hydrophobic surfaces A novel optical diffuser based on cellulose nanocrystals (CNCs) embedded in polydimethylsiloxane (PDMS) matrix, or cellulose nanocrystal:polymer (CNP) is reported. By offering simple low-cost fabrication process as well as compatibility with large-scale production, the proposed optical diffuser is a better choice for integration into optoelectronic devices for light management compared to other cellulose-based diffusers due to its physical durability and the lack of requirement for index-matching between the diffuser and the optoelectronic device thanks to the unique surface properties, mechanical flexibility, and optical transparency offered by PDMS as the matrix material. It is demonstrated that CNCs are an excellent filler material to pair up w...

An application‐oriented roadmap to select polymeric nanocomposites for advanced applications: A review

“…The extraction process of cellulosic fibers by either mechanically or chemically induced produces nanomaterials called CNFs and cellulose nanocrystals (CNCs), respectively. Although CNFs present high aspect ratio for flexible filaments, CNCs occur as rod-like [247] Natural rubber in latex form…”

“…Recent studies have started to focus also on the light scattering properties of CNCs. [247] The study presented in reference [244] provides a summary of almost 40 different polymer matrixes of CNC-based nanocomposites and the corresponding rheological properties. The important information on CNCs from the recent literature studies is collected and presented in Table 26.…”

Transparent nanocellulose metamaterial enables controlled optical diffusion and radiative cooling

“…In particular, the nanosized version cellulose nanofibrils (CNF) has been in the spotlight owing to its interesting combination of properties, including optical transparency, biocompatibility, low density, and high tensile strength. [1][2][3] These properties make CNF suitable for various electronic and bioelectronic applications, 1,2 and it has also been explored for optical applications in the areas of electronic displays, structural coloration and many other. [4][5][6][7][8][9][10][11][12][13] The ability to scatter light with minimal absorption losses enables a material to be used as optical diffuser.…”

“…[12][13][14][15][16][17][18][19][20][21] Motivated by major drawbacks of current diffuser technologies, such as high processing costs and low transmission efficiency, nanocellulose-based systems have been proposed and investigated as promising alternatives. 3,4,12,13 While transparent in the visible, cellulose instead provides strong absorption in the infrared due to molecular vibrations (e.g., C-O-H bending, C-O stretch, CH 2 wagging, and CQO stretch). 22,23 The corresponding high thermal emissivity makes cellulose-based materials suitable for passive radiative cooling, which so far was only sparsely reported 24 and to our knowledge not previously investigated for nanocellulose composites.…”

Unveiling the Photophysical Properties of Boron Heptaaryldipyrromethene Derivatives

“…Organic optoelectronic materials are of great interest for organic light‐emitting diodes (OLEDs), organic field‐effect transistors (OFETs),, as well as nonlinear optical (NLO) devices, because of their relatively low cost, tunable emission wavelength and efficiency, ease of fabrication and integration into devices, fine‐tuned chemical structures . On the other hand, the continuous performance improvement for these applications strongly correlates with the enhancement of optoelectronic property in such materials ,. Consequently, increasing research activities and much effort has been made to discover novel compounds with the desirable performance …”