I. Abstract of the Paper’s Core Research

This work employs the honeycomb‑structured Mott insulator α‑RuCl₃ as the functional material and establishes a two‑step process comprising intercalation‑based electronic doping followed by megasonic exfoliation of nanosheets. Coupled with aerosol jet printing (AJP), this approach enables the fully printed fabrication of near‑infrared photodetectors featuring both electrodes and photosensitive channels. The materials are systematically characterized in terms of their crystal structure, nanosheet morphology, thin‑film electrical properties, and near‑infrared detection performance. The key findings are as follows:

Two‑step intercalation–based electronic doping调控 of the RuCl₃ band structure

Phase I: Electrochemical intercalation—three types of quaternary ammonium salts, THAB, TDAB, and TDDAB, are embedded into bulk RuCl₃. The larger intercalants expand the interlayer spacing, while the smaller molecules enable high‑level carrier doping. Phase II: Ultrasonic exfoliation—PVP undergoes secondary intercalation, further increasing the electron concentration, narrowing the optical bandgap, and achieving efficient near‑infrared light absorption at 1550 nm.

Preparation of Ultrathin, Printable RuCl₃ Nanosheets via Exfoliation

MHz‑frequency ultrasonic cavitation exfoliation yields thinner nanosheets compared with conventional ultrasound (the TDDAB system achieves an average thickness of only 2.24 nm); the IPA‑based eco‑friendly ink formulation contains no high‑residue CHP solvents, is compatible with stable aerosol atomization, and remains clog‑free over extended periods.

All-in-One Printed Optoelectronic Device Based on Aerosols

AJP sequentially prints graphene conductive electrodes and a RuCl₃ photosensitive channel, with the PI flexible substrate directly formed in a single step. By precisely controlling the number of printing layers, a film thickness of 3.5 μm—optimal for the photosensitive layer—is achieved, yielding the highest photocarrier transport efficiency.

Millisecond-level rapid near-infrared detection performance

Under a 1550 nm light source, the optimized TDDAB-based device achieves a responsivity of 244 mA/W—more than ten times that of conventional solution‑processed two-dimensional photodetectors. Its rise and fall times are as low as 160 ms and 130 ms, respectively, while maintaining stable photocurrent output even in low‑light conditions.

Transient photon annealing for low‑damage post‑processing

Millisecond‑pulse‑width xenon‑lamp annealing rapidly decomposes surface‑layer PVP residues while preventing RuCl₃ from losing activity due to dechlorination, thereby preserving a high dopant‑induced carrier concentration in the film and ensuring long‑term stability under ambient air conditions.

II. Complete Process Flow for Aerosol-Printed RuCl₃ Near-Infrared Detectors

Electrochemical Intercalation of Bulk RuCl₃: Three quaternary ammonium bromide salts (THAB, TDAB, and TDDAB) are intercalated into the crystal lattice, thereby expanding the interlayer spacing and achieving primary electronic doping.

Megasonic liquid-phase exfoliation: The DMF system is subjected to megasonic agitation for 2 hours, followed by a second intercalation step performed concurrently with PVP; the solvent is then replaced with isopropanol to prepare an aerosol‑compatible ink.

Aerosol Equipment Commissioning: Ultrasonic atomization system, with terpineol added to regulate the drying rate; nozzle diameter 200 μm; substrate maintained at a constant temperature of 45°C.

Layered printing: First, graphene interdigitated electrodes are fabricated via aerosol jet printing, followed by the printing of an RuCl₃‑based photosensitive active channel.

Photon Rapid Annealing: 2.0 kV pulsed xenon lamp, 1.36 ms short-term thermal treatment to remove surface PVP;

Complete characterization: XR/XPS/Raman analyses are used to characterize the intercalation‑doping structure; AFM measures the thickness of nanosheets; a 1550 nm infrared light source is employed to assess the photoelectric response; and scanning photocurrent mapping is utilized to evaluate device uniformity.

III. Five Core Process Advantages of Aerosol Jet Printing for Fabricating Optoelectronic Devices

All-device maskless digital integrated printing

The electrode and the photosensitive layer are fabricated in a single process step using the same equipment, eliminating the need for costly wafer‑level processes such as photolithography, metal evaporation, and lift‑off, thereby enabling rapid prototyping on flexible substrates.

Compatible with ultra-thin two-dimensional nanosheet inks, enabling controllable porosity in the formed films.

Low-velocity droplet deposition does not disrupt the layered structure of RuCl₃; the printed thickness can be linearly tuned by adjusting the number of deposition cycles, enabling precise matching to the optimal thickness for maximum light absorption.

Non-contact low-temperature forming compatible with flexible PI substrates.

The entire process is carried out at room temperature, with only a millisecond‑scale photonic annealing step performed afterward; no high‑temperature baking is required, ensuring that the polyimide film remains undeformed and uncarbonized.

Material utilization has improved significantly, resulting in substantial savings of precious-metal feedstock.

Site-specific, on-demand deposition of photosensitive and conductive inks significantly reduces R&D costs compared to the large-area waste associated with spin coating and vacuum deposition.

Compatible with multiple materials; graphene and two-dimensional halides can be printed simultaneously.

An aerosol-based system enables the hetero-integration of conductive electrodes and a semiconductor photosensitive layer, supporting the iterative development of various two-dimensional optoelectronic devices.

IV. Five Core Technological Innovations of This Study

Innovation 1: A Two‑Level Intercalation–Coordinated Electronic Doping System

First, an electrochemical layer‑growth step is performed, followed by simultaneous sonication and a second PVP‑based doping. This dual‑mode control of the RuCl₃ carrier concentration significantly enhances near‑infrared photovoltaic conversion efficiency.

Innovative 2 MHz ultrasonic exfoliation ink technology for ultra-thin nanosheets

Unlike conventional kHz‑ultrasonic methods, this approach yields few‑layer, high‑quality RuCl₃ with no interlayer stacking, and significantly enhances the stability of ink atomization.

Innovative New Paradigm for All-Printed Two-Dimensional Near-Infrared Detectors Based on Aerosol Technology

Achieve additive manufacturing of a complete device comprising an RuCl₃ photosensitive layer and graphene electrodes, overcoming the limitations of vacuum‑based fabrication equipment.

Innovative 4-millisecond photon-assisted low-temperature annealing process

Short‑time pulsed thermal treatment removes polymer residues, avoids high‑temperature dechlorination and decomposition of RuCl₃, and balances electrical conductivity with material stability.

Innovative 5 1550 nm Ultra-High-Response Photodetection Scheme for Printing

The TDDAB interlayer architecture achieves an ultra‑high near‑infrared responsivity of 244 mA/W, setting a new record for printed two‑dimensional photodetectors.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Conventional two-dimensional ink‑based materials exhibit thick layers and severe stacking, leading to substantial recombination losses of photogenerated carriers.

✅ High-frequency ultrasonic exfoliation yields ultrathin RuCl₃ nanosheets with a thickness of ~2 nm, featuring continuous conductive pathways in the thin film and a significant enhancement in photocurrent.

Challenge 2: Near-infrared two-dimensional materials (black phosphorus) are prone to oxidation in air, resulting in short device lifetimes.

✅RuCl₃ exhibits excellent chemical stability, with no degradation even after prolonged exposure to air, eliminating the need for encapsulation or protective packaging.

Challenge 3: The photolithography and evaporation processes are complex, resulting in high production costs for flexible infrared chips.

✅ Maskless direct writing of aerosols, one-click CAD switching to device layouts, and no need for custom masks in small‑batch R&D.

Challenge 4: High residual surfactant on the printed film surface increases interfacial contact resistance.

✅ Millisecond-scale photonic transient annealing rapidly decomposes the surface PVP layer without disrupting the internal doping structure of RuCl₃.

Challenge 5: Conventional solution‑processed devices generally exhibit insufficient near‑infrared responsivity, typically below 10 mA/W.

✅ Two‑stage intercalation narrows the bandgap, enhances 1550 nm light absorption, and improves responsivity by an order of magnitude.

VI. Future Diversified Industrial Application Scenarios

1 Flexible Fiber-Optic Communication Infrared Detection Array

Wearable communication module featuring a 1550 nm optical receiver chip, with a thin, curved‑surface integration that replaces rigid silicon‑based detectors.

2 Minimally Invasive Endoscopic Bioimaging Chip

Medical micro‑flexible probe, enabling non‑invasive near‑infrared imaging of biological tissues, with a significantly reduced footprint.

3 IoT Micro Infrared Sensing Node

Passive miniature photonic sensor, designed for distance sensing and ambient infrared monitoring, with ultra-low power consumption and capable of being mounted directly onto substrates.

4 Printing Flexible Optoelectronic Array Laboratory R&D Platform

Rapidly switch intercalation formulations and fabricate, in batch, RuCl₃‑doped photodetectors to accelerate the screening of two-dimensional optoelectronic materials.

5 Automotive LiDAR miniature photosensitive unit

1550 nm laser‑receiving microchip, a lightweight component for flexible circuits in automotive radar systems.

Image and Text Guide

• RuCl₃ is a Mott insulator (with a band gap of approximately 1 eV); intercalation-induced electron doping introduces new bands near the Fermi level, resulting in near-infrared light response.
• THAB exhibits the smallest interlayer spacing (d ≈ 20 Å) and the highest degree of doping, while TDDAB shows the largest interlayer spacing (d ≈ 34 Å) and the greatest expansion; XPS peak shifts and XRD‑derived expansion trends provide a complementary explanation for this trade-off.
• After intercalation, the antiferromagnetic coupling weakens as charge is injected (the Néel temperature decreases from 13.4 K to approximately 3.7 K).

• Compared with conventional liquid-phase exfoliation at the kHz level, megahertz‑level ultrasonic exfoliation yields more localized and stable cavitation, resulting in a higher yield of thin nanosheets.
• TDDAB exhibits the largest swelling, the lowest exfoliation energy barrier, and yields the thinnest nanosheets (2.24 nm) after mechanical exfoliation.
• PVP serves a dual role as both a stabilizer and a secondary intercalation–reduction agent: it intercalates into the interlayer spaces and coats the nanosheets, thereby providing additional electronic doping.

• The optimal photon‑annealing conditions are 2.0 kV/1.36 ms (1.87 J/cm²): this fully removes surface PVP to ensure percolative conductivity while preserving interlayer PVP to maintain doping.
• Excessively high energy density (2.33 J/cm²) causes dechlorination of RuCl₃ and a sharp drop in photocurrent; conversely, too low an energy density (1.47 J/cm²) results in insufficient removal of PVP.
• The peak of the SPCM photocurrent is located at the center of the channel, with negligible contributions from the contact regions, indicating an ohmic contact between graphene and RuCl₃.

• After MSE treatment, TDDAB‑intercalated devices exhibit the highest overall electronic doping; their responsivity at 1550 nm reaches 244 mA/W, surpassing that of previously reported solution‑processed 2D photodetectors by more than an order of magnitude.
• Sublinear power dependence (with a more negative γ) arises from charge trapping induced by the PVP; the responsivity increases as the light intensity decreases.
• The photocurrent increases with the number of printing passes and then reaches saturation; seven passes (≈3.5 μm), corresponding to the absorption path length, represent the optimal thickness.