Researchers from the University of British Columbia, led by Shoumik Debnath, have recently published a study in the journal “ACS Photonics” that explores ways to improve the efficiency of lead-free perovskite light-emitting diodes (PeLEDs) for near-infrared (NIR) applications. The team, which includes Sudipta Saha, Khondokar Zahin, Ying Yin Tsui, and Md. Zahurul Islam, focuses on optimizing these materials for use in wearable and flexible optoelectronic devices.
The study centers on CsSn$_x$Ge$_{1-x}$I$_3$ perovskites, which are promising for next-generation NIR emitting PeLEDs due to their tunable bandgaps and stability. However, these materials currently suffer from poor light extraction efficiency, and there is a lack of accurate composition-specific optical data. To address these issues, the researchers developed a framework that combines density functional theory (DFT) calculations with finite-difference time-domain (FDTD) simulations.
First, the team performed DFT calculations to obtain composition-specific complex refractive index and extinction coefficient values for different compositions of CsSn$_x$Ge$_{1-x}$I$_3$ (where x ranges from 0 to 1). They found that the bandgap increased from 1.331 eV for CsSnI$_3$ to 1.927 eV for CsGeI$_3$ as the germanium content increased, while the refractive index ranged from 2.2 to 2.6 across the different compositions.
Using these optical constants, the researchers then conducted FDTD simulations of a PeLED structure with optimized gold/silica (Au/SiO$_2$) core-shell nanorods for plasmonic enhancement. They achieved a significant 12.1-fold Purcell enhancement for the CsSn$_{0.25}$Ge$_{0.75}$I$_3$ composition, while the light extraction efficiency reached 25% for CsSn$_{0.5}$Ge$_{0.5}$I$_3$. Additionally, they observed a light extraction efficiency enhancement of 36% for CsSnI$_3$ and a spectral overlap between the emitter and plasmon resonance of up to 96% for tin-rich compositions.
The design guidelines derived from this study suggest that CsSn$_{0.5}$Ge$_{0.5}$I$_3$ offers the best balance of extraction efficiency (25%), Purcell enhancement (5.3 times), spectral overlap (93%), and oxidation stability for wearable and flexible optoelectronic applications. On the other hand, CsSn$_{0.25}$Ge$_{0.75}$I$_3$ is recommended for applications that prioritize spontaneous emission rate.
For the energy sector, particularly in the development of advanced lighting and display technologies, this research offers practical applications by providing a pathway to enhance the efficiency of lead-free perovskite LEDs. The insights gained from this study can help in designing more efficient and stable NIR emitting devices, which are crucial for various optoelectronic applications, including sensing, communication, and medical devices. The optimization of these materials can contribute to the development of more energy-efficient and sustainable lighting solutions.
This article is based on research available at arXiv.