# Harnessing Metallic Nanoparticle-Based Anodes for Red-Shifting and Reshaping Electroluminescence toward the Near-Infrared Region

## TL;DR

This paper introduces a method to create near-infrared OLEDs using silver nanoparticles and TiO2 coatings, enabling color-tunable light emission without needing specialized materials.

## Contribution

The study introduces a stacking coating technique that enables broad-wavelength NIR emission using Ag nanoparticle-based anodes.

## Key findings

- Ag nanoparticles showed stronger LSPR responses and greater color-tunability than Au nanoparticles.
- The overcoating method red-shifted the emission peak from 663 to 723 nm with 12.91% external quantum efficiency.
- TiO2 stacking produced a broad EL spectrum (643–842 nm) with a full width at half maximum of 199 nm.

## Abstract

Leveraging conventional red-emitting materials, a color-tuning
strategy is used to develop high-performance near-infrared (NIR) organic
light-emitting diodes (OLEDs). This study presents a practical approach
for achieving color-tunable optically impaired OLEDs through localized
surface plasmon resonance (LSPR), which extends the emission of red-emitting
materials into the NIR region, thereby eliminating the need for dedicated
NIR emitters. The method utilizes silver (Ag) and gold (Au) nanoparticle-based
anodes modified with titanium dioxide (TiO2) coatings under
various rapid thermal annealing (RTA) treatments (200 °C, 400
°C, and 600 °C). Three TiO2 coating techniquesovercoating,
stacking, and sandwichingwere compared in terms of their influence
on the LSPR behavior and electroluminescence (EL) spectra. UV–vis
spectroscopy, including transmittance and absorbance analyses, confirmed
that the different coating methods facilitated LSPR formation and
thus modulated EL characteristics and induced distinct spectral features.
Ag nanoparticles exhibited stronger LSPR responses and greater color-tunability
than Au nanoparticles. Scanning electron microscopy revealed that
RTA promoted island-like nanoparticle growth and minimized agglomeration,
while TiO2 coatings enhanced island formation, resulting
in well-defined and narrower absorbance peaks. The overcoating approach
successfully red-shifted the primary emission peak of red phosphorescent
OLEDs from 663 to 723 nm, achieving a maximum external quantum efficiency
of 12.91% and a low turn-on voltage (V
on) of 2.41 V. Furthermore, a broad EL emission spectrum (full width
at half maximum = 199 nm) spanning 643–842 nm was achieved
using the TiO2 stacking configuration. These findings highlight
the potential of Ag nanoparticle-based anodes for color-tunable NIR
OLEDs and introduce a stacking coating technique with potential for
broad-wavelength applications.