Inverted Solution-Processed Quantum Dot Light-Emitting Devices with Wide Band Gap Quantum Dot Interlayers
Mohsen Azadinia1, Tyler Davidson-Hall1, Dong Seob Chung1
1Department of Electrical and Computer Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
ACS Applied Materials & Interfaces
|May 4, 2023
Summary
Adding a quantum dot interlayer to inverted quantum dot light-emitting devices (IQLEDs) with polymeric hole transport layers (HTLs) significantly boosts efficiency and device lifetime by addressing electron leakage and exciton quenching.
Area of Science:
- Materials Science
- Optoelectronics
- Nanotechnology
Background:
- Polymeric hole transport layers (HTLs) are beneficial for device fabrication in inverted quantum dot light-emitting devices (IQLEDs).
- However, their use often results in poor device performance due to issues at the HTL interface.
- Previous assumptions attributed poor performance to solvent damage, which this study refutes.
Purpose of the Study:
- To identify the primary causes of poor performance in IQLEDs utilizing polymeric HTLs.
- To develop a strategy to mitigate interface-related issues and enhance IQLED performance.
- To gain deeper insights into charge injection mechanisms and their dependence on quantum dot (QD) properties.
Main Methods:
- Investigated the role of a wider band gap QD interlayer (IL) between the HTL and emission material layer (EML).
- Fabricated and characterized IQLEDs with and without the IL, measuring efficiency and operational lifetime.
- Conducted single-carrier device measurements and ultraviolet photoelectron spectroscopy (UPS) to analyze charge injection and energy levels.
Main Results:
- The IL effectively facilitates hole injection, suppresses electron leakage, and reduces exciton quenching at the HTL interface.
- IQLEDs with the IL showed a 2.85× increase in efficiency (3% to 8.56%) and a 9.4× improvement in lifetime (1266 to 11,950 h).
- Charge injection analysis revealed that electron injection is easier with smaller band gap QDs, while hole injection becomes more difficult, correlating with QD band alignment.
Conclusions:
- The primary cause of poor performance in polymeric HTL-based IQLEDs is interface-related issues, not solvent damage.
- A wider band gap QD interlayer is a simple yet effective method to significantly enhance IQLED performance.
- The study provides crucial insights into QD band gap-dependent charge injection and HTL interface properties in different device architectures.
