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Molecular Packing Dictates One-Step vs Two-Step Triplet Sensitization for Photon Upconversion at the Organic/2D
Min Xu1, Cheng Sun1, Guoyu Xiang1
1State Key Laboratory of Extreme Photonics and Instrumentation, Zhejiang Key Laboratory of Excited-State Energy Conversion and Energy Storage, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310058, China.
ACS Nano
|October 11, 2025
Summary
Molecular packing in organic/2D semiconductor heterostructures critically impacts near-infrared photon upconversion. Different packing structures dictate distinct triplet sensitization pathways, influencing efficiency for optoelectronic applications.
Area of Science:
- Materials Science
- Organic Electronics
- 2D Semiconductors
Background:
- Near-infrared (NIR) photon upconversion via triplet-triplet annihilation (TTA) is crucial for light harvesting and optoelectronics.
- Understanding triplet sensitization mechanisms at organic/2D semiconductor interfaces is vital but underexplored.
- The influence of molecular packing on these processes remains largely unknown.
Purpose of the Study:
- To investigate the role of molecular packing in rubrene/WSe2 heterostructures on NIR-to-visible photon upconversion.
- To elucidate the distinct triplet sensitization mechanisms and dynamics influenced by different rubrene phases (orthorhombic, monoclinic, amorphous).
- To establish design principles for optimizing solid-state photon upconversion.
Main Methods:
- Fabrication and characterization of rubrene/WSe2 heterostructures with varying rubrene phases.
- Ultrafast spectroscopy to probe triplet sensitization dynamics.
- Ultraviolet photoelectron spectroscopy (UPS) and optical measurements to analyze interfacial electronic structures.
Main Results:
- NIR-to-visible photon upconversion was observed in both orthorhombic (Orth) and monoclinic (Mono) rubrene/WSe2 heterostructures.
- Orth heterostructures exhibited a two-step indirect charge-transfer-mediated triplet sensitization (5.3 ps hole transfer, 67 ps electron transfer) with 86% triplet energy transfer (TET) quantum yield.
- Mono heterostructures showed a one-step direct Dexter energy transfer mechanism with a slower rate (20 ps) and 47% TET quantum yield.
- Interfacial band alignment, particularly the highest occupied molecular orbital (HOMO) level, was modulated by molecular π-stacking and intermolecular coupling, influencing the sensitization pathway.
Conclusions:
- Molecular packing is a critical, overlooked factor governing triplet sensitization pathways and efficiencies at organic/2D semiconductor interfaces.
- Different rubrene phases lead to distinct interfacial electronic structures and consequently, different photon upconversion mechanisms.
- This study provides fundamental insights and design guidelines for developing efficient solid-state photon upconversion devices.
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