In a remarkable advancement poised to reshape the landscape of short-wavelength infrared (SWIR) detection, researchers at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, have unveiled a novel organic semiconductor material that dramatically extends light absorption into the SWIR region. This breakthrough addresses a long-standing challenge in the field: engineering organic photodetectors (OPDs) capable of efficient and broad SWIR response, a feat traditionally dominated by high-cost inorganic semiconductor technologies such as InGaAs. Through meticulous molecular design and innovative end-group chemistry, the team, led by Professor Jun Liu, successfully harnessed J-aggregation to push the absorption spectrum significantly beyond typical organic limits, heralding a new era of flexible, cost-effective, and high-performance SWIR photodetection.
The significance of this achievement cannot be overstated. SWIR photodetection underpins critical applications ranging from non-invasive medical imaging and autonomous vehicle navigation to secure optical communications. While InGaAs and other III–V semiconductor-based photodetectors excel in performance metrics, their dependence on complex epitaxial manufacturing, high material costs, and inherent mechanical rigidity constrain their widespread adoption, especially in emerging fields demanding flexible and lightweight components. Organic photodetectors have long promised a solution, owing to their low processing costs, tunable optical properties, and mechanical flexibility. However, extending their response beyond approximately 1000 nm has remained an elusive goal, primarily due to the intrinsic limitations of molecular semiconductors in harvesting longer-wavelength photons.
Professor Liu and colleagues’ study presents a paradigm shift by exploiting a newly synthesized molecule named NBN-4, a thiophene-fused BODIPY tetramer equipped with meta-dicyanophenyl end groups that promote J-aggregation—a molecular packing motif characterized by head-to-tail arrangement of chromophores resulting in narrow, highly red-shifted absorption bands. This strategic cyanation end-group modification enhances the local dipole moment within the molecule to an impressive 7.64 Debye, markedly strengthening intermolecular electrostatic interactions. These interactions encourage robust J-aggregation, which cooperatively extends light absorption deep into the SWIR region, precisely measured at an absorption peak of 1205 nm. This elegant molecular engineering therefore overcomes a critical bottleneck in organic semiconductor photophysics.
Leveraging this molecular design, the NBN-4-based OPDs attain a peak responsivity of 0.15 A W⁻¹ and a specific detectivity nearing 4.78×10¹¹ Jones at 1200 nm—metrics that place these devices among the highest performing purely organic SWIR photodetectors reported to date. The superior detectivity reflects an optimized balance between light absorption, exciton generation, charge separation, and charge transport, all enabled by the tailored molecular structure. Such high detectivity in flexible and solution-processable materials offers immense potential for scalable manufacturing of infrared sensors beyond the confines of rigid, inorganic counterparts.
Delving deeper into the molecular phenomena underpinning this performance, the team applied a suite of computational and spectroscopic techniques. Density functional theory calculations revealed that the increased local dipole moment fostered tighter molecular packing within the solid-state film, facilitating efficient charge separation by mitigating recombination pathways. Ultrafast transient absorption spectroscopy further illuminated the photophysical dynamics, demonstrating a significantly accelerated exciton dissociation rate and more rapid hole transfer dynamics in the NBN-4 blend compared to control molecules lacking the end-group cyanation. These combined effects synergize to enhance charge carrier mobility and reduce loss mechanisms, crucial for achieving high responsivity under SWIR illumination.
This work not only spotlights the pivotal role of molecular end-group engineering but also emphasizes the power of J-aggregation in organic semiconductors for extending optical response. Unlike traditional strategies focusing solely on extending π-conjugation or altering backbone structures, the cyanation-induced J-aggregation accomplished here exemplifies a subtle yet highly effective tactic for modulating intermolecular interactions to tailor device-relevant properties. Professor Liu underscores this, remarking that “precisely engineered oligomer frameworks combined with tailored end-group chemistry represent a versatile and generalizable route to achieving J-aggregation, thereby enabling broadband organic semiconductor optical response well into the SWIR range.”
The implications of this breakthrough reverberate across numerous technological domains. The organic photodetectors built from NBN-4 exhibit not only outstanding SWIR sensitivity but also the intrinsic advantages of solution processability and mechanical flexibility. This positions them as frontrunners for integration into wearable electronics, biomedical monitoring devices requiring non-invasive infrared sensing, and artificial vision systems demanding lightweight and conformable photodetectors. Importantly, the material’s compatibility with scalable manufacturing methods like printing or coating advances the prospect of large-area flexible infrared sensor arrays at dramatically reduced costs.
Moreover, this innovation paves the way for future investigations into the design principles governing molecular aggregation and optical tuning within organic semiconductors. By elucidating how end-group modification impacts electronic dipoles and packing motifs, this study provides a blueprint for tailoring other classes of organic photonic materials toward customized spectral and electronic functionalities. The cyanation-driven J-aggregation concept may inspire new families of organic semiconductors extending beyond SWIR detection into applications like photovoltaics, photothermal therapy, and optoelectronic devices where precise control over absorption characteristics is paramount.
The researchers’ adoption of multifaceted experimental characterization complemented by theoretical modeling exemplifies a comprehensive approach to organic semiconductor research. This synergy between molecular synthesis, advanced spectroscopy, and computational chemistry continues to be instrumental in accelerating the discovery of high-performance materials with targeted optoelectronic properties. The insights gained here regarding local dipole enhancement and molecular packing effects can serve as guiding principles in the rational design of future organic materials with tailored functionalities.
In summary, the introduction of the NBN-4 molecule and its associated J-aggregation-induced spectral extension addresses one of the critical challenges limiting organic photodetectors’ applicability in the SWIR regime. Achieving peak responsivity and detectivity metrics rivaling those of established inorganic detectors, while maintaining the benefits of cost-effective, flexible, and lightweight devices, marks a significant milestone. As Professor Liu and the team look forward, they anticipate that this cyanation-driven aggregation strategy will catalyze the development of next-generation organic semiconductors fueling advances in infrared sensing technologies and beyond—opening new frontiers for wearable health monitoring, autonomous navigation, and secure communication systems.
This study, recently published in Science Bulletin, epitomizes the intersection of fundamental molecular science and practical device engineering, showcasing how subtle chemical design can unlock transformative functional properties in organic electronics. The promise of integrating these high-performance materials into flexible platforms stands to revolutionize the accessibility and application scope of SWIR photodetection, making it more ubiquitous and versatile than ever before.
Subject of Research: Organic semiconductors for short-wavelength infrared photodetection.
Article Title: Molecular Design Promoting J-Aggregation Enables Efficient Organic Photodetection at 1200 nm.
Web References: DOI: 10.1016/j.scib.2025.10.043
Keywords
Short-wavelength infrared; organic photodetectors; J-aggregation; molecular design; cyanation; BODIPY tetramer; dipole moment; exciton dissociation; charge separation; solution processing; flexible electronics; SWIR sensing
