Collecting Plasmonic Near-Infrared Photons through a Schottky junction

Project Information

INFRALIGHT

Grant agreement ID: 101152448

DOI

10.3030/101152448

Project terminated on 30 November 2025

EC signature date 15 April 2024

Start date 1 September 2024

End date 31 August 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 172 750,08

Coordinated by

FONDAZIONE ISTITUTO ITALIANO DI TECNOLOGIA
Italy

Periodic Reporting for period 1 - INFRALIGHT (Collecting Plasmonic Near-Infrared Photons through a Schottky junction)

Reporting period: 2024-09-01 to 2026-08-31

Summary of the context and overall objectives of the project

More than one third of the solar energy reaching the Earth lies beyond the 1000 nm wavelength range. Efficient harvesting of infrared (IR) photons is therefore a critical and largely untapped opportunity for improving photovoltaic performance, photoelectric conversion efficiency, and next-generation imaging and communication technologies. Despite substantial progress in infrared optoelectronics, current IR detection and harvesting technologies remain constrained by material toxicity, high cost, and limited scalability. In recent years, colloidal quantum dots have emerged as a cost-effective alternative to conventional infrared semiconductors such as InGaAs, InSb, and HgCdTe. However, the vast majority of these approaches rely on toxic heavy-metal chalcogenides containing lead, cadmium, or mercury. This reliance poses serious environmental and regulatory challenges, particularly in the context of mass-market deployment. In line with the European Union’s Restriction of Hazardous Substances (RoHS) Directive (2002/95/EC), there is an urgent need to develop infrared optoelectronic technologies based on sustainable, heavy-metal-free materials that comply with environmental regulations while maintaining high performance. Doped metal oxide nanocrystals, such as tin-doped indium oxide (ITO), have recently gained attention as a promising class of heavy-metal-free plasmonic materials. Owing to their high free-carrier densities, these nanocrystals exhibit tunable localized surface plasmon resonances across the near-infrared (NIR) and short-wave infrared (SWIR) spectral regions. Importantly, doping-induced band bending at the nanocrystal surface enables efficient generation of plasmon-induced hot carriers under infrared excitation. While plasmonic materials have been extensively integrated with semiconductors for visible-light applications, their systematic exploitation in the infrared regime-particularly using heavy-metal-free plasmonic nanomaterials-remains largely unexplored. The INFRALIGHT project addresses this critical gap by introducing a new optoelectronic architecture based on a Schottky junction formed between semiconducting fluorographene and heavy-metal-free doped metal oxide nanocrystals (e.g. Sn-doped In2O3). This junction is designed to enable efficient extraction of plasmon-generated hot electrons under infrared illumination, even at zero external bias. By leveraging infrared plasmonic hotspots in the nanocrystals, the project aims to demonstrate a proof-of-concept self-powered photodetector operating in the NIR-SWIR range.
The overall objective of INFRALIGHT is twofold: (i) to establish fundamental understanding of infrared plasmon-charge-transfer processes at doped metal oxide/2D semiconductor interfaces (for example: fluorographene), and (ii) to translate this understanding into scalable, environmentally compliant optoelectronic devices. By moving beyond purely optical demonstrations and toward functional device integration, the project will open new pathways for sustainable infrared photodetection technologies. From an impact perspective, INFRALIGHT directly contributes to European strategic priorities in advanced materials, sustainable electronics, and green digital technologies. Scientifically, it will deliver new insights into infrared plasmonics and hot-carrier dynamics in hybrid nanostructures. Technologically, it will provide a platform for low-cost, heavy-metal-free infrared photodetectors compatible with large-area fabrication. In the longer term, the project’s outcomes are expected to support the development of environmentally responsible infrared technologies for sensing, energy harvesting, and communication, thereby strengthening Europe’s competitiveness in next-generation optoelectronics.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Scientific and Technical Details
The synthesized fluorographene was extensively studied to address its stability limitations. To improve stability, a graphene/fluorinated graphene heterostructure (Gr/F-Gr HS) was developed. The fluorination process and the resulting material properties were systematically investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). Raman spectroscopy provided initial evidence of the fluorination process through the emergence of sp³-related vibrational modes, indicating the conversion of sp2 carbon to sp3 bonding. This observation was further confirmed by X-ray photoelectron spectroscopy, where the appearance of a distinct F1s core-level peak unambiguously verified the presence of fluorine in the fluorinated graphene layer. Ultraviolet photoelectron spectroscopy measurements revealed that the fluorinated graphene exhibited insulating behaviour after fluorination. However, upon formation of the graphene/fluorinated graphene heterostructure, the electronic structure showed a restoration of conductivity, highlighting the beneficial role of the heterostructure configuration. Comprehensive analysis of the experimental results indicated the presence of electrostatic interactions between the graphene and fluorinated graphene layers. Due to these interactions, a fraction of fluorine atoms was found to bind to the top graphene layer. This phenomenon contributes to the stabilization of the heterostructure and is consistent with the defect passivation mechanism in fluorinated bilayer systems. In addition, ultraviolet-visible (UV-Vis) absorption spectroscopy was employed to examine the optical response before and after fluorination. A reduction in optical absorption was observed following fluorination, consistent with the transition toward an insulating state. Notably, the graphene/fluorinated graphene heterostructure exhibited an enhanced optical absorption, demonstrating the advantageous optical properties of the heterostructure architecture. The electrical properties of fluorographene system is also investigated and it is found that the Gr/F-Gr HS has better electrical properties than only F-Gr.
The synthesized Sn-doped In2O3 nanocrystals optical, structural, and electrical properties were investigated. The Sn-doped In2O3 nanocrystals exhibited a pseudo-spherical morphology with a well-controlled, monodisperse size distribution. Optical absorption measurements showed a pronounced absorption peak located within the target infrared wavelength region, confirming their suitability for infrared optoelectronic applications. The electrical properties of the Sn-doped In2O3 nanocrystals were systematically investigated to evaluate charge transport behavior and inter-nanocrystal interactions. The results demonstrated that thermal annealing significantly improves the electrical performance of the nanocrystal films by enhancing nanocrystal confinement and interparticle coupling, leading to improved charge transport characteristics. Finally, heterostructures composed of graphene (Gr), fluorographene (F-Gr), and graphene/fluorographene (Gr/F-Gr) were successfully integrated with Sn-doped In2O3 nanocrystals using a simple and scalable spin-coating technique, establishing the material platform required for subsequent optoelectronic device fabrication.
The main Achievement of INFRALIGHT
1. Successful synthesis and optimization of heavy-metal-free nanomaterials, including semiconducting fluorographene and Sn-doped In2O₃ nanocrystals, within the planned project timeframe.
2. Development of wafer-scale semiconducting fluorographene using a newly established plasma fluorination technique, extending beyond the initially proposed XeF2-based approach and enabling fabrication on rigid, transparent, and flexible substrates.
3. Demonstration of enhanced stability through graphene/fluorographene heterostructures (Gr/F-Gr), supported by comprehensive spectroscopic analysis (Raman, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy), revealing defect passivation and favourable electrostatic interlayer interactions.

4. Establishment of tunable infrared plasmonic behavior in Sn-doped In2O3 nanocrystals, with controlled morphology, monodisperse size distribution, and optimized electrical properties via post-synthesis annealing.
5. Successful integration of graphene-based materials with Sn-doped In2O₃ nanocrystals through scalable spin-coating techniques, enabling the fabrication of hybrid heterostructures suitable for infrared optoelectronic device architectures.
6. Creation of a robust material and device platform for investigating plasmon-induced hot-carrier generation and charge transfer mechanisms in heavy-metal-free infrared optoelectronic systems.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The INFRALIGHT project has delivered several results that go beyond the current state of the art, advancing both fundamental understanding and technological capability in infrared optoelectronics based on heavy-metal-free materials. A major scientific and technological breakthrough achieved within the project is the development of wafer-scale semiconducting fluorinated graphene, realized through a newly established SF₆ plasma-based fluorination process. This result goes significantly beyond the originally proposed scope and represents a substantial innovation for semiconductor technology. Wafer-scale fluorinated graphene combines tunable electronic properties with improved material stability and compatibility with scalable fabrication processes, addressing key limitations of existing two-dimensional semiconductors. This advancement opens new opportunities for large-area, environmentally compliant infrared optoelectronic devices.
Another important result beyond the state of the art is the systematic investigation of stability enhancement through graphene/fluorinated graphene heterostructures (Gr/F-Gr). For the first time, transient absorption spectroscopy was employed to study charge-carrier dynamics in fluorinated graphene and Gr/F-Gr heterostructures. Remarkably, the heterostructure exhibited pronounced absorption in the short-wave infrared (SWIR) region, where the individual graphene and fluorinated graphene layers show limited optical response. This finding reveals a new pathway for infrared light–matter interaction in graphene-based heterostructures and represents a previously unexplored optical regime. In parallel, Sn-doped In2O3 nanocrystals demonstrated strong and tunable infrared plasmonic absorption, aligning spectrally with the SWIR response of the Gr/F-Gr heterostructures. The coexistence of infrared plasmonic hotspots in the nanocrystals and enhanced SWIR absorption in the heterostructure creates favorable conditions for plasmon-induced hot-carrier generation and extraction, a regime that has not yet been experimentally explored. This combined material system provides a unique platform for studying nanoscale infrared energy localization and charge transfer. Looking ahead, further uptake and exploitation of these results will benefit from advanced near-field characterization techniques, such as scanning near-field optical microscopy (SNOM), to directly probe infrared plasmonic hotspots and hot-carrier dynamics at the nanoscale. Additional research is required to translate these findings into fully functional device demonstrators, including optimization of interfaces, device architectures, and long-term operational stability. From a broader perspective, the results of INFRALIGHT position heavy-metal-free plasmonic nanomaterials and fluorinated graphene heterostructures as promising building blocks for sustainable infrared technologies, with strong potential for future commercialization following targeted device demonstration, intellectual property development, and alignment with regulatory and standardization frameworks.

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