Efficiency of Polymer Light-Emitting Diodes: A Perspective.
Bas Van der Zee1, Yungui Li1, Gert-Jan A H Wetzelaer1
1Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz, 55128, Germany.
Advanced Materials (Deerfield Beach, Fla.)
|November 17, 2021
Summary
Triplet-triplet annihilation (TTA) significantly boosts external quantum efficiency (EQE) in polymer light-emitting diodes (PLEDs). This study demonstrates TTA
Area of Science:
- Organic Electronics
- Materials Science
- Photophysics
Background:
- External quantum efficiency (EQE) in polymer light-emitting diodes (PLEDs) is determined by electrical efficiency, photoluminescence quantum yield (PLQY), and optical outcoupling.
- Existing PLED device models and optical simulations estimate EQE but do not fully account for observed efficiencies in fluorescent PLEDs.
- Discrepancies between measured and predicted EQEs, particularly in systems like super-yellow poly(p-phenylene vinylene) (SY-PPV) PLEDs, indicate missing factors.
Purpose of the Study:
- To investigate the discrepancy between measured and predicted external quantum efficiencies (EQEs) in fluorescent polymer light-emitting diodes (PLEDs).
- To determine the contribution of triplet-triplet annihilation (TTA) to the overall EQE in PLEDs.
- To refine the electrical device model for PLEDs by incorporating TTA mechanisms.
Main Methods:
- Utilized a numerical PLED device model to analyze electrical efficiency.
- Employed an optical model to simulate photon outcoupling efficiency in PLEDs.
- Integrated triplet-triplet annihilation (TTA) into the electrical PLED model to explain experimental observations.
Main Results:
- Measured EQEs in fluorescent PLEDs, such as SY-PPV, often exceed values predicted by standard models.
- Incorporating triplet-triplet annihilation (TTA) into the PLED model resolves the discrepancy between predicted and measured EQEs.
- Experimentally, TTA was found to contribute approximately 40% to singlet-exciton generation efficiency in SY-PPV PLEDs, increasing EQE to ~4% from an expected 2.5%.
Conclusions:
- Triplet-triplet annihilation (TTA) plays a crucial role in enhancing the external quantum efficiency (EQE) of fluorescent polymer light-emitting diodes (PLEDs).
- The inclusion of TTA in device modeling is essential for accurately predicting PLED performance.
- TTA provides a significant pathway for increasing singlet exciton generation, leading to higher EQEs in PLED devices.
