Enhancing the Overall Performances of Blue Light-Emitting Electrochemical Cells by Using an Electron-Injecting/Transporting Ionic Additive

Light-emitting electrochemical cells (LECs) have emerged as a promising emissive thin-film technology for next-generation solid-state lighting. However, blue LECs show low performances, which has remained a bottleneck for the fabrication of white LECs for lighting applications. Here, we demonstrate a remarkable enhancement of overall device performance for blue LECs by using an electron-injecting/transporting ionic additive, that is, [Zn­(bpy)₃]­(PF₆)₂ (bpy is 2.2′-bipyridine, PF₆^– is hexafluorophosphate). It is revealed that adding [Zn­(bpy)₃]­(PF₆)₂ into the active layers of blue LECs accelerates the device response, simultaneously enhances the brightness and efficiency, reduces the efficiency roll-offs, significantly improves the blue color stability upon the continuous electrical operation, and enhances the device operational stability at optimized conditions. The remarkable enhancement of the overall device performance upon adding [Zn­(bpy)₃]­(PF₆)₂ results from facilitated electron injection/transport and thus more balanced electron–hole recombination and more centered recombination zone, as well as the reduction of phosphorescence concentration quenching in the LECs. The work demonstrates for the first time that the use of electron-injecting/transporting ionic additives such as [Zn­(bpy)₃]­(PF₆)₂ is a facile yet effective strategy to remarkably boost the overall performances of blue LECs

Fitted curves of the spectrum from the 70° Bi₂Te₃ tip, with the fitted sub-peaks of tip plasmons (green), bulk/substrate emission (light blue), and edge plasmons (dark blue), respectively.

The fitted peak position of tip plasmons is 413.61 nm. (TIF)</p

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Bi2Te3, as a topological insulator, is able to support plasmonic emission in the visible spectral range. Thin Bi2Te3 flakes can be exfoliated directly from a Bi2Te3 crystal, and the shape of Bi2Te3 flakes can be further modified by focused ion beam milling. Therefore, we have designed a Bi2Te3 triangular antenna with distinct tip angles for the application of plasmonic resonance. The plasmonic emission of the Bi2Te3 triangular antenna is excited and investigated by cathodoluminescence in the scanning electron microscope. Enhanced tip plasmons have been observed from distinct tips with angles of 20º, 36º, 54º, 70º, and 90º, respectively. Due to the confinement of geometric boundaries for oscillating charges, the resonant peak position of tip plasmon with a smaller angle has a blue shift. Moreover, the dependence of plasmonic behavior on the excitation position has been discovered as well. This research provides a unique approach to fabricate Bi2Te3 nanostructures and manipulate the corresponding plasmonic properties.</div

Fitted curves of the spectrum from the 20° Bi₂Te₃ tip, with the fitted sub-peaks of tip plasmons (green), bulk/substrate emission (light blue), and edge plasmons (dark blue), respectively.

The fitted peak position of tip plasmons is 377.56 nm. (TIF)</p

CL spectra excited at four spots along the angle bisector of the 36° tip.

Excitation locations are shown in the inserted SEM image. The color of each curve matches with the color of excitation spots.</p

Fitted curves of the spectrum from the 54° Bi₂Te₃ tip, with the fitted sub-peaks of tip plasmons (green), bulk/substrate emission (light blue), and edge plasmons (dark blue), respectively.

The fitted peak position of tip plasmons is 401.58 nm. (TIF)</p

Schematic of the CL characterization process accompanied inside a SEM chamber.

Schematic of the CL characterization process accompanied inside a SEM chamber.</p

(a) EDX spectrum of the same Bi₂Te₃ flake; (b) CL spectra collected from the center of the Bi₂Te₃ flake and the substrate.

(a) EDX spectrum of the same Bi2Te3 flake; (b) CL spectra collected from the center of the Bi2Te3 flake and the substrate.</p

S1 File -

Bi2Te3, as a topological insulator, is able to support plasmonic emission in the visible spectral range. Thin Bi2Te3 flakes can be exfoliated directly from a Bi2Te3 crystal, and the shape of Bi2Te3 flakes can be further modified by focused ion beam milling. Therefore, we have designed a Bi2Te3 triangular antenna with distinct tip angles for the application of plasmonic resonance. The plasmonic emission of the Bi2Te3 triangular antenna is excited and investigated by cathodoluminescence in the scanning electron microscope. Enhanced tip plasmons have been observed from distinct tips with angles of 20º, 36º, 54º, 70º, and 90º, respectively. Due to the confinement of geometric boundaries for oscillating charges, the resonant peak position of tip plasmon with a smaller angle has a blue shift. Moreover, the dependence of plasmonic behavior on the excitation position has been discovered as well. This research provides a unique approach to fabricate Bi2Te3 nanostructures and manipulate the corresponding plasmonic properties.</div

(a) SEM image and (b-d) EDX maps of the Bi₂Te₃ triangular nanoflake with three different angles on a Si substrate.

(a) SEM image and (b-d) EDX maps of the Bi2Te3 triangular nanoflake with three different angles on a Si substrate.</p