I. Abstract of the Paper’s Core Research

In this work, MoS₂ thin films with three different thicknesses—10 nm, 50 nm, and 100 nm—were prepared by magnetron sputtering. An n‑MoS₂/p‑Si heterojunction was fabricated on a p‑type silicon substrate, and silver fork‑shaped electrodes were patterned via aerosol jet printing. Comprehensive characterization—including the film’s microstructure, optical bandgap, dark I–V characteristics, and photoelectric response under illumination—was systematically performed. The key findings of this study are as follows:

The thickness of MoS₂ determines the crystallinity and defect density of the thin film.

At 10 nm, the ultrathin film exhibits fine grain size and a surface roughness of only 1.08 nm, with the lowest Urbach energy, a bandgap of 1.6 eV, and a low density of interband localized defects. As the thickness increases to 50 and 100 nm, grain agglomeration and surface roughness rise, disordered defects become more prevalent, the electron–phonon coupling strength continues to increase, and radiative recombination of photogenerated carriers is exacerbated.

Thickness directly modulates the rectifying electrical properties of heterojunctions.

The 10-nm device exhibits an ideality factor of 1.13, a rectification ratio as high as 1.32×10³, uniform barrier profiles, and extremely low current‑carrying recombination losses; in contrast, for 50-nm and 100-nm films, the number of defects increases, leading to ideality factors that rise to 1.68 and 1.87, respectively, with elevated leakage currents and a marked deterioration in rectification performance.

Photovoltaic output performance decreases with increasing thickness.

Under AM1.5 standard illumination, the photoelectric conversion efficiency is 0.85% for a 10-nm device, 0.72% for a 50-nm device, and only 0.56% for a 100-nm device; numerous defects within the thick film trap photogenerated electrons and holes, leading to a substantial reduction in the short-circuit current.

Aerosol electrodes offer multiple advantages over vacuum-based processes.

Vacuum‑free, maskless digital direct‑write interdigitated electrodes with fine line features and reduced shading area significantly enhance device light‑absorption efficiency while lowering wafer‑fabrication costs and equipment investment.

Full Thickness – Optoelectronic Quantitative Correlation System

A comprehensive correlation model linking thin-film thickness, surface roughness, Urbach defects, rectification characteristics, and photovoltaic efficiency has been established, providing standardized data to support the selection of optimal film thicknesses for MoS₂‑based silicon photovoltaic devices.

II. Complete Preparation Procedure for MoS₂/p-Si Heterojunction Aerosols

Substrate Pre-treatment: P-type silicon wafers are cleaned, followed by magnetron sputtering to deposit a 200-nm-thick gold back electrode, and then subjected to rapid thermal annealing at 300°C to form an ohmic contact.

Magnetron Sputtering Deposition of MoS₂ Thin Films: High-purity MoS₂ target, with a substrate temperature of 600°C; film thickness is precisely controlled via sputtering time, offering options of 10/50/100 nm.

Aerosol ink formulation of commercial silver‑nanoparticle conductive paste, using the Optomec AJ5X system with a 300‑μm nozzle for direct‑write interdigitated electrodes.

The electrode was sintered on a hot plate at 200°C for 1 hour to remove the solvent and enhance the electrical conductivity of the silver film.

Complete characterization: XRD, XPS, and AFM were used to analyze the thin film’s structure and morphology; UV–vis–NIR spectroscopy was employed to measure optical absorption; and dark‑state and illuminated I–V curves were recorded to determine the diode’s rectification and photovoltaic parameters.

III. Five Core Process Advantages of Electrode Fabrication via Aerosol Jet Printing

Manufactured at ambient pressure without vacuum, significantly reducing capital expenditure on production-line equipment.

By eliminating the need for high‑vacuum chambers such as electron‑beam evaporation or thermal evaporation, desktop‑level aerosol‑based equipment can directly print metal electrodes, sharply reducing R&D costs for small and medium‑scale production runs.

Maskless digital direct writing eliminates the need for multiple photolithography and lift-off steps.

CAD‑based customization of interdigitated electrode patterns eliminates the need for custom photomasks, enabling rapid iteration of electrode structures with varying line widths and spacings.

Fine, narrow-line electrodes reduce light-blocking losses.

The aerosol beam‑focusing precision is high, and the electrode lines are finer; compared with sputtering a continuous metal film, this significantly reduces the light‑blocking area and enhances the device’s light absorption.

Compatible with a variety of hard substrates, including silicon and glass, enabling conformal deposition without damaging the MoS₂ two-dimensional film.

Non-contact droplet deposition, with no mechanical stress, prevents scratching of the ultra-thin MoS₂ functional layer.

High consumable utilization and low precious-metal ink waste.

Precise silver‑line deposition in designated areas significantly reduces nano‑silver paste waste compared with full‑area sputtering, resulting in lower long‑term prototyping costs.

IV. Five Core Technological Innovations of This Study

Innovation 1: Aerosol‑Jet‑Deposited Silver Electrodes for MoS₂/p‑Si Heterojunction Devices

Breaking with the conventional approach to vacuum electrode fabrication for two-dimensional silicon-based optoelectronic devices, we demonstrate the feasibility of additive manufacturing of electrodes under ambient pressure.

Innovation 2: A Multi-Dimensional Quantitative Analysis System for Thin-Film Defects

The differences in thin-film disorder arising from thickness are quantitatively characterized using the Urbach energy, the steepness parameter, and the electron–phonon coupling coefficient as three complementary metrics.

Innovation 3: Ultra-thin 10 nm MoS₂—Optimal Device Window Clearly Defined

It is conclusively demonstrated that ultrathin, low-defect films can significantly reduce current‑carrying recombination, thereby simultaneously enhancing rectification characteristics and photoelectric conversion efficiency.

Innovation: Joint Modeling of Three I‑V Analysis Methods

By simultaneously extracting the barrier height and series resistance using the lnI–V, Norde, and Cheung models, the electrical parameters are calculated with greater accuracy and reliability.

Innovation 5 Thickness – Photoelectricity-Driven Database

Establish reusable thickness selection criteria to provide experimental evidence for the process optimization of two-dimensional silicon-based photodetectors and thin-film solar cells.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Conventional vacuum electrode fabrication equipment is costly, the associated lithography process is complex, and the prototyping cycle is lengthy.

✅ Aerosol-based, ambient-pressure maskless printing enables electrode fabrication on a single device, eliminating the need for vacuum deposition and photolithography.

Challenge 2: The metal electrodes deposited across the entire device surface cause severe light shading, resulting in low optical absorption efficiency.

✅ Aerosol‑printable ultrafine interdigitated electrodes with significantly reduced electrode shading area, enhancing the short-circuit current.

Challenge 3: Thick MoS₂ films exhibit numerous defects, leading to severe recombination of photogenerated carriers and a pronounced decline in optoelectronic performance.

✅The experiment defines an optimal thickness range of 10 nm for ultra-thin films, which exhibit low roughness and few defects, thereby suppressing carrier recombination.

Challenge 4: There is no quantitative benchmark for the thickness of two-dimensional films and their impact on device performance, leaving process optimization entirely reliant on trial-and-error.

✅Establish a comprehensive database linking film thickness, defects, rectification, and photovoltaic performance, enabling rapid identification of the optimal sputtering duration.

Challenge 5: Vacuum high-temperature coating can easily damage the ultrathin two-dimensional layered structure of MoS₂.

✅ Aerosol-assisted room-temperature deposition of electrodes, enabling low-temperature processing throughout the entire process without compromising the crystal structure of functional thin films.

VI. Future Diversified Industrial Application Scenarios

1 Silicon-based near-infrared miniature photodetector

10-nm MoS₂ combined with aerosol‑based fine electrodes enables low‑cost fabrication of miniature imaging and infrared‑sensing chips.

2 Small-Scale Two-Dimensional Silicon Thin-Film Solar Cells

Development of lightweight, flexible and rigid micro‑photovoltaic devices, along with the mass production of portable micro‑power sources.

3 MEMS Optoelectronic Sensor Array

Wafer-level batch printing of interdigitated electrodes and rapid prototyping of multi-channel optofluidic microchips.

4 High-Throughput R&D Platform for Two-Dimensional Material Devices in the Laboratory

Rapidly fabricate metal electrodes of various specifications and perform batch testing of MoS₂ devices with different thicknesses.

5 Wearable Flexible Optoelectronic Sensing Patch

Conformal printing of conductive circuits using a flexible‑substrate, gel‑based ink; a device for monitoring weak physiological light signals.

Image and Text Guide

• (a) Process Route :p-Si substrate → sputtered Au back electrode (200 nm, 300 °C RTA for 1 min) → RF magnetron sputtering of MoS₂ films with varying thicknesses → AJP-printed Ag interdigitated electrode (Optomec AJ5X, 300 μm nozzle, 200 °C hotplate sintering for 1 h).
• (b) Device Parameters Device dimensions: 4.6 × 4.6 mm²; interdigitated electrode line width: 500 μm, pitch: 100 μm, finger length: 750 μm.
• The use of maskless, vacuum-free AJP for electrode fabrication can significantly reduce device manufacturing costs.

• All samples are in   2θ = 13.8°   A single diffraction peak appears, corresponding to the (002) crystal plane of the hexagonal molybdenum disulfide structure.
• As the film thickness increases, the intensity of the (002) peak increases—indicating improved crystallinity of the film.
• XRD results provide strong evidence for the formation of MoS₂ crystals in the sputtered thin film.

• The surfaces of the three‑thickness films are composed of grains with uniform size and consistent distribution.
• As the thickness increases, grains grow and coalesce into larger grains: the RMS roughness rises from 1.08 nm at 10 nm to 1.81 nm at 100 nm, while the grain size increases from 13.5 nm to 24.5 nm.
• A 10-nm-thick film with the lowest surface roughness exhibits reduced light scattering and high transmittance, which is more conducive to the performance of electro-optical devices.

• (a) Transmission spectrum : Within the 200–1100 nm range, the thicker the film, the lower its transmittance—thicker films exhibit stronger absorption of incident light.
• (b) Absorption spectrum : Absorption increases with thickness, consistent with the fact that longer optical path lengths and increased surface roughness allow more photons to enter the structure.
• (c–e) Tauc method : The optical bandgaps of the 10/50/100 nm thin films are, respectively,   1.60, 1.55, 1.50 eV — The thinner the film, the wider the bandgap, which is associated with reduced grain size and a lower local density of states.

• (a) : The Urbach energy Eᵤ is determined from the reciprocal of the slope of the lnα–hν plot; as the thickness increases, Eᵤ rises from 0.104 eV to 0.113 eV—indicating an increase in structural disorder and defect density.
• (b) : The steepness parameter σ decreases with increasing thickness (0.395 → 0.341), while the electron–phonon coupling energy Eₑ₋ₚ increases (1.687 → 1.956 eV)—a trend associated with the rise in defect-state density.

• (a) All devices exhibit pronounced rectifying behavior—the MoS₂/p-Si interface forms a well‑formed Schottky junction.
• (b) : Within the forward bias range of 0–1 V, three linear regions can be identified: Region I (0–0.1 V) is dominated by dark current; Region II (0.1–0.3 V) is dominated by recombination current; and Region III (>0.3 V) is dominated by series resistance.
• 10 nm devices deliver optimal performance. Rectification ratio   1.32×10³ , ideal factor  1.13 (Near-perfect diode); the rectification ratio decreases slightly with increasing thickness.

• (a) Norde function : The barrier height ΦB and the series resistance Rs are calculated from the minimum value of F(V).
• (b,c) Cheung function : ΦB and Rs are calculated from the slopes and intercepts of the straight lines obtained by plotting dV/dln(I)–I and H(I)–I, respectively; the results from the two methods are consistent.
• Series resistance: For 10-nm devices, it is approximately 20–25 Ω (Norde/Cheung); for 100-nm devices, it increases slightly to about 20–51 Ω; the barrier height is roughly 0.57–0.61 eV.

• Power conversion efficiency of devices with three different thicknesses: 10 nm 0.85%, 50 nm 0.72%, 100 nm 0.56% — Increasing the thickness, on the contrary, leads to a decline in photovoltaic performance.
• The Jsc reaches a maximum at 50 nm and then declines rapidly with increasing thickness—due to the increased defect density and recombination in thicker films, which impede carrier transport.
• Compared with conventional grid electrodes, AJP-printed electrodes exhibit reduced light shading and can further optimize the power conversion efficiency (PCE) by tuning the line width and pitch.