Ultrahigh-resolution, high-fidelity quantum dot pixels patterned by dielectric electrophoretic deposition

Abstract

The high pixel resolution is emerging as one of the key parameters for the next-generation displays. Despite the development of various quantum dot (QD) patterning techniques, achieving ultrahigh-resolution (>10,000 pixels per inch (PPI)) and high-fidelity QD patterns is still a tough challenge that needs to be addressed urgently. Here, we propose a novel and effective approach of orthogonal electric field-induced template-assisted dielectric electrophoretic deposition to successfully achieve one of the highest pixel resolutions of 23090 (PPI) with a high fidelity of up to 99%. Meanwhile, the proposed strategy is compatible with the preparation of QD pixels based on perovskite CsPbBr₃ and conventional CdSe QDs, exhibiting a wide applicability for QD pixel fabrication. Notably, we further demonstrate the great value of our approach to achieve efficiently electroluminescent QD pixels with a peak external quantum efficiency of 16.5%. Consequently, this work provides a general approach for realizing ultrahigh-resolution and high-fidelity patterns based on various QDs and a novel method for fabricating QD-patterned devices with high performance.

Fig. 1. Dielectric electrophoretic deposition process.

Schematic diagrams of a the polarization of PEGDA-QDs under an electric field, b the conventional electrophoretic deposition, and c the dielectric electrophoretic deposition (DED) process of QDs. Fluorescence microscopy images of QD patterns under various electric field frequencies of d 10 kHz, e 100 kHz, and f 1 MHz, respectively

Fig. 2. Template-assisted DED process.

a Schematic diagram of the stripe template-assisted DED process. b Scanning electron microscopy (SEM) image of the stripe templates and fluorescence microscopy images of QD patterns on the templates c without and d with the electric field (4 V mm⁻¹, 100 kHz). Dynamic secondary ion mass spectrometry (SIMS) of the elements of Pb, Cs, and Si in the areas of the e groove and f edge on the templates. g Fluorescence microscopy images of QD patterns with the QDs concentrations at 20 (top) and 15 (down) mg mL⁻¹, respectively

Fig. 3. QD pixel fabrication.

Schematic diagram of the template-assisted QD pixel deposition process successively driven by a X- and b Y-axis electric field, c QD pixel patterns after the orthogonal electric field, and d–f the corresponding scanning electron microscopy (SEM) images of the square grooves after applying the electric field (inset: the groove depth along the dotted line characterized by a step profiler). Fluorescence microscopy images of g the CsPbBr₃ QD pixels and the h enlarged view of the rectangular area in (g), i red CdSe QD pixels. j–l Different QD pixel resolutions fabricated by the proposed strategy with around 23, 14, and 0.8 μm in length for the QD resolutions of 705, 1162, and 23,090 PPI, respectively

Fig. 4. Device performance.

a–d Schematic of the fabrication process of QD pixel-based QLEDs, and e the device structure. Illustration of the leakage current without (f) and with (g) PDMS. h The current density–voltage (J–V) curves of the devices with and without PDMS. The device performances: i current density–luminance–voltage (J–L–V) and j efficiency–current density (EQE–J) curves. k The normalized EL spectra under different voltages (inset: the picture of the device during the test)