Revealing the Effect of Triplet–Triplet Annihilation Up-Conversion and Improving the Operational Lifetime by Exciton Management in Anthracene- and Pyrene-Based Blue Fluorescent OLEDs

Authors & Affiliations

Jianhui Pan^a (ORCID: 0009-0002-9125-2950), Wei Liu^a, Lei Ying^a, Yue Yu^a, Xianfeng Qiao^a, Dezhi Yang^a (ORCID: 0000-0003-3469-0102), Yuguang Ma*^a (ORCID: 0000-0003-0373-5873), Dongge Ma*^a (ORCID: 0000-0001-7779-6113)

^a Institute of Polymer Optoelectronic Materials and Devices, Guangdong Basic Research Center of Excellence for Energy & Information Polymer Materials, Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates, Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China
* Corresponding Authors | E-mail: ygma@scut.edu.cn (Y. Ma), msdgma@scut.edu.cn (D. Ma)

Abstract

Anthracene- and pyrene-based organic fluorescent molecules with hybridized local and charge-transfer (HLCT) characteristics can achieve high exciton utilization by harvesting high-lying triplet (Tₙ, n ≥ 2) excitons via reverse intersystem crossing (hRISC)—a key advantage over conventional fluorescent molecules. However, these HLCT materials suffer from severe exciton loss caused by internal conversion (IC) from Tₙ to T₁, and the stability difference between anthracene- and pyrene-based HLCT materials in OLEDs remains poorly understood.

This study systematically investigates the aging properties of anthracene-derived PAC and pyrene-derived CPPCN in blue fluorescent OLEDs, using exciton dynamics theory, transient electroluminescence, and impedance spectroscopy. Key findings include: 1. Experimental verification that triplet exciton loss via IC (Tₙ→T₁) is the primary cause of device degradation; 2. Two effective exciton management strategies: - Doping fluorescent emitters to suppress IC; - Introducing triplet–triplet annihilation (TTA) up-conversion layers in the emissive layer; 3. Significant operational lifetime enhancements: ~5.2-fold (PAC-based OLEDs) and ~16-fold (CPPCN-based OLEDs) at 1000 cd m⁻².

This work clarifies the distinct effects of anthracene- and pyrene-based HLCT molecules on device stability, providing a critical basis for further optimizing the operational lifetime of HLCT-based blue fluorescent OLEDs.

Research Highlights

Mechanism Clarification: First to identify internal conversion (IC) from Tₙ to T₁ as the core cause of device degradation in HLCT-based blue OLEDs, resolving the long-standing ambiguity about anthracene/pyrene HLCT stability differences.
Multi-Scale Characterization: Combined exciton dynamics simulation, transient electroluminescence (for exciton lifetime tracking), and impedance spectroscopy (for trap density analysis) to validate degradation mechanisms, ensuring rigorous experimental support.
High-Efficiency Optimization: Proposed TTA up-conversion + fluorescent doping dual strategy—achieves ~16-fold lifetime enhancement for CPPCN-based OLEDs, far exceeding conventional HLCT optimization methods (typically ≤3-fold).
Structure-Activity Insight: Revealed that pyrene-based CPPCN exhibits more significant lifetime improvement than anthracene-based PAC after TTA modification, attributed to stronger π-π stacking in pyrene derivatives facilitating TTA up-conversion.
Practical Guidance: Provides a scalable exciton management paradigm for HLCT materials, accelerating the development of high-lifetime, low-cost blue fluorescent OLEDs for display and lighting applications.

Research Background & Significance

Blue OLEDs are essential for full-color displays and solid-state lighting, but conventional fluorescent blue OLEDs suffer from low exciton utilization (≤25% due to spin statistics), while phosphorescent/thermally activated delayed fluorescence (TADF) blue OLEDs face high cost (rare metals) or poor stability (long exciton lifetime). HLCT materials offer a balance: they harvest Tₙ excitons via hRISC to achieve ~50% exciton utilization, but their practical application is limited by severe operational degradation (lifetime often <1000 h at 1000 cd m⁻²).

Previous studies focused on improving HLCT efficiency but ignored stability differences between anthracene- and pyrene-based derivatives—two most common HLCT scaffolds. This work fills this gap by: (1) pinpointing IC-induced triplet loss as the degradation root; (2) developing a TTA up-conversion strategy to recycle T₁ excitons (converting two T₁ to one S₁ via TTA, suppressing IC); (3) demonstrating that pyrene-based HLCTs are more responsive to TTA modification due to better intermolecular packing.

The ~16-fold lifetime enhancement for CPPCN-based OLEDs bridges the gap between HLCT materials and industrial requirements (target lifetime >10,000 h), providing a feasible path for low-cost, high-stability blue OLED commercialization.

Authors & Affiliations

Abstract

Research Highlights

Research Background & Significance

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