Heterogeneous Integration of Three-Primary-Color Photoluminescent

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Surfaces, Interfaces, and Applications

Heterogeneous Integration of Three-primary-color Photoluminescent Nanoparticle Arrays with Defined Interface Zeying Zhang, Meng Su, Qi Pan, Zhandong Huang, Wanjie Ren, Zheng Li, Zheren Cai, Yifan Li, Fengyu Li, Lihong Li, and Yanlin Song ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b16884 • Publication Date (Web): 12 Dec 2018 Downloaded from http://pubs.acs.org on December 12, 2018

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ACS Applied Materials & Interfaces

Heterogeneous Integration of Three-primary-color Photoluminescent Nanoparticle Arrays with Defined Interface Zeying Zhang†,1,2,Meng Su†1*, Qi Pan,1,2 Zhandong Huang,1 Wanjie Ren,1,2 Zheng Li,1,2 Zheren Cai,1,2 Yifan Li,1,2 Fengyu Li,1 Lihong Li,1 Yanlin Song1,2* 1

Key Laboratory of Green Printing, CAS Research/Education Center for Excellence in

Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China. 2

University of Chinese Academy of Sciences, Beijing 100049, P. R. China

†

These authors contributed equally to this work.

*Corresponding

author. Email: [email protected] (M.S.), [email protected] (Y.S.)

KEYWORDS: Heterogeneous, Integration, Three-primary-color, Arrays, Defined interface

ABSTRACT

Minimized photoluminescent devices require both high-density fluorescent arrays and minimal cross-talk between neighboring pixels on the limited area. However, the challenges to achieve

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the overall integration of nanomaterials-based devices hinder the development of microscale fullcolor displays, including micro/nanoarray density, orientation control, multimaterials interface morphology and uniform colors. Here, we report a heterogeneous integration approach to control the orientation, combination and density of fluorescent micro/nanoarrays on flexible substrates. Through controlling the defined interface and critical shrinkage width of liquid bridges, the width of three-primary-color micro/nanolines reaches 100 nm. The interval between two parallel luminous lines is down to 40 μm, and the optical cross-talk effect is remarkably reduced. This work provides a facile approach to prepare high performance micro-photoluminescent and imaging arrays for next-generation flexible display and lighting technology.

1. INTRODUCTION Minimized optoelectronic devices are intensively pursued owing to their unique optical properties1,2 and the promising applications in photodetectors,3 sensors,4 waveguides,5 lasers6 and displays.7 These multilayer photoluminescent devices require high-density and minimal optical cross-talk effect between neighboring luminous pixels.8 It is critical to regulate wellordered micro/nano architectures with controlled morphology,9 clearly defined interfaces10,11 and designed functional components.12 Over decades, many versatile methods for the fabrication of photoluminescent devices have been developed, including photolithography,13 soft lithography14 and laser-induced thermal imaging.15 These methods usually require UV light exposure or thermal sintering,16 which are difficult to produce heterogeneous integration of different functional components on flexible substrates.17 In recent years, the solution self-assembly technology with self-assembly of nanomaterials has been developed,18-20 which is a directpatterning way for high throughput and various materials.21 Moreover, 1D nanoparticle-


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assembled architectures with different morphologies have been achieved via the printing method.18 However, it is still a challenge to precisely control the multimaterials interface at the microscale during the continuous self-assembly process.22,23 Another difficulty is how to eliminate the blurs and errors in the overlapping and crossing definition of different interfaces,24 which exacerbate the cross-talk effect.25,26 Here, we proposed a facile printing approach for heterogeneous integration of various fluorescent nanoparticles-based micro/nanoarrays with controllable multilayer orientation, combination and density. By controlling the height of the liquid bridges, the multiassembly micro/nanolines covered the previous printed arrays at a contrasting equal width. Heterogeneous integration would be achieved in crossing micro/nanoarrays by the successive printing processes of different fluorescent nanoparticles. The characteristic dimension of these micro/nanoarrays can be down to 100 nm, while the single pixel at the cross point is 445 nm. After precisely registering disparate elements from different solutions, three-primary-color arrays with defined interface are achieved to promote the luminescent color purity and reduce the cross-talk effect. 2. RESULTS AND DISCUSSION 2.1 A Schematic of the Full Printing Strategy Used to Fabricate Three-primary-color Micro-photoluminescent Arrays. As shown in Figure 1, different fluorescent nanoparticles can be integrated by successively printing with retention of their individual photoluminance intensity, which has the excellent processing compatibility with lightweight, flexible plastic substrates. Printing templates are independently adopted during the first, second and third printing processes, while nanoparticlesbased micro/nanoarrays show clearly defined interfaces between two different color lines. Three-


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primary-colors (red, green and blue) micro/nanoarrays are crossed to form yellow, cyan, magenta and white pixels at the integration sites for optical panchromatic micro-pallet with minimum cross-talk. The interval length (I) between two lines varied from 40 μm to 200 μm, while the line width (D) is varied from 100 nm to 4 μm, which can be well controlled by the printing templates and concentrations of the nanoparticles suspensions. Accordingly, the microarrays with a total of 93750 luminous cross points over an area of 1.5 cm2 are achieved. The length and the width of each primary color microline are 1.5 cm and 1 μm, respectively, with interval of 40 μm. The microarrays can be printed on a variety of rigid or flexible substrates. 2.2 Sequential Recording Optical Microscope Images of the Successive Printing Process. Self-assembly of functional nanoparticles in inks is an effective method for micro- and nanofabrication.

After

investing

the

Rayleigh-instability-induced

transformation

of

nanomaterials during the dewetting process, one dimensional nanowires can be successively processed.27,

28

In this case, green fluorescent nanoparticles in the printed ink were firstly

assembled on a glass substrate. The solid/liquid/gas three-phase contact line (TCL) could be manipulated by the pillar-patterned structures on the template (Figure S1),29 which provided regular confined space for different fluorescent nanoparticles self-assembling (Figure S2).30 The printing process was monitored in real time by video recording (Figure 2a-e). Then, the red fluorescent nanoparticles suspension (1-10 mg/ml) was filled in the gap between the substrate with previous printed microlines (green boxes in Figure 2a) and the printing template (yellow circles in Figure 2a). The first printed nanoparticles after 145 oC sintering in 45 mins were not impacted during the spreading process of the second dropping suspension. The sintered nanoparticles have strong adhesion among nanoparticles and the substrate. With the evaporation of water, the nanoparticle ink was separated into several liquid bridges by the curved solid-


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liquid-gas TCL. The hydrophilic pillars on the templates pinned the TCL, while the TCL could slide on the hydrophobic substrates. (Figure S3) Thus, liquid bridges were formed between the pillars on the template and the firstly printed green microlines on the substrate, which also provided separate confined space for nanoparticles assembling. (Movie S1) After the completed evaporation of water, the red nanoparticles self-assembled into the closepacked microlines. (Figure 2e and Movie S2) The cross points from the combination of green and red fluorescent nanoparticles can be used as micro-photoluminescent pixels with clearly defined interface. Figure 2f shows the single-nanoparticle width nanoline and nanoparticlesaggregated submicron line. Single pixel size is down to 445 nm from the heterogeneous integration of two micro/nanolines. The red nanoparticle microlines were also sintered to improve the adhesion on the substrate. Finally, three-primary-color microarrays were achieved by repeating above steps with the blue fluorescent nanoparticles. To achieve the defined interface, nanoparticles-based micro/nanolines have to be bonded together after the previous printing processes, which has the materials limitations in the practical application. 2.3. Morphology Diagram of Heterogeneous Integration of Cross Points. So far, the fabrication of three-primary-color micro-photoluminescent devices via the selfassembly of nanoparticles has been still a great challenge in the precise control of different functional layers interfaces.31 Blurs and errors in the overlapping and crossing definition of micro/nanoarrays would make photoluminescent arrays unclear and exacerbate the cross-talk effect.32 The second printing nanoparticles-based micro/nanolines covered the previous printed arrays at a contrasting equal width by controlling the height of the liquid bridge (H).33 (Figure 3a) When the contraction of the liquid bridge reaches a critical state and keeps in the


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equilibrium, the surface energy of the liquid bridges is the minimum. The geometric relationship of the menisci is dependent on the H, the critical shrinkage width (L), the contact angle (θ) and the radius of micropillars (r, which is the fixed value of 5 µm) as follows:

H=

𝐿𝑐𝑜𝑠 𝜃 + 4𝑟𝐿(1 ― 𝑠𝑖𝑛 𝜃) ― 4𝑟2(1 ― 𝑠𝑖𝑛 𝜃)2 2(1 ― 𝑠𝑖𝑛 𝜃)

（1）

The theoretical analysis indicates that the critical width increases with the height of the liquid bridge at the constant contact angle. (details in the Theoretical analysis in the Supporting Information) The influence of the contact angle on the critical shrinkage width was also investigated. The L will decrease when increase θ at the constant H, and the relationship can be obtained from the calculation. (Figure 3b) In order to form uniform micro/nanoarrays with the equal width, the substrate was treated at the medium contact angle (50°

Heterogeneous Integration of Three-Primary-Color Photoluminescent

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