Aerosol Jet Printing of the Active Layer in Polymer Solar Cells, ACS Applied Materials & Interfaces
Product Introduction
Equipment Parameters
I. Core Research Abstract
- Solvent Formulation Optimization : Single‑component dichlorobenzene (DCB) readily forms micron‑scale particle protrusions due to rapid solvent evaporation; incorporating a high‑boiling 1,8‑octanedithiol additive can significantly enhance polymer crystallinity without the need for thermal annealing, yielding P3HT‑based devices with a power conversion efficiency of 2.53% and a fill factor as high as 67%.
- Revolutionary Conclusions on the Annealing Process : The native thin film of the aerosol has completed molecular self-assembly; high‑temperature thermal annealing induces excessive phase separation in the active layer, leading to performance degradation. Only solvent vapor annealing can effectively optimize the charge‑carrier transport pathways in the PCBTDPP system. After annealing with a DCB/chlorobenzene mixed solvent, small‑area devices achieve an efficiency of 3.92%, while a 1 cm² large‑area module stably delivers 3.14%.
- Process Advantage Verification Aerosol printing is maskless, compatible with inks of a wide viscosity range, features an adjustable nozzle–substrate gap, and is resistant to clogging. It enables the continuous, large-area fabrication of uniform polymer active layers, demonstrating the technology’s potential for industrial-scale organic photovoltaics.
II. Complete Operating Principle of Aerosol Jet Printing
- Ultrasonic atomization generates microdroplets.
45W ultrasonic vibration at 30°C generates ultrafine aerosol droplets with a diameter of approximately 15 μm; nitrogen, used as the carrier gas (at 14–20 psi), transports these droplets to the printing nozzle.
- Sheath gas–airflow focused beam
The nozzle injects coaxial sheath gas at 8–12 psi, forming an annular airflow that encapsulates the aerosol plume and compresses and focuses the microdroplets. Its key advantage is fully addressing the persistent issue of nozzle clogging due to drying in inkjet printing, enabling long‑term continuous operation. The print head can be positioned 3–5 mm from the substrate, making it compatible with curved and uneven surfaces.
- Base deposition for film formation
The sample stage is maintained at a constant temperature of 40°C, and microdroplets are rapidly impacted onto the substrate to form a liquid film; the film thickness can be precisely controlled by adjusting the ink concentration, the pressure of the carrier/protective gas, the platform’s travel speed, and the number of printing passes.
- Post-processing molding
The printed thin film can be either used directly or subjected to solvent‑vapor annealing, after which a metal cathode is deposited via vacuum evaporation to complete the device. Unlike spin coating, this process requires no mask throughout; custom CAD‑designed patterns are digitally printed directly.
III. Key Technological Innovations of This Study
Innovation 1: High-performance devices achieved through annealing without thermal treatment, simplifying production-line processes.
Innovation 2: Precise Control of Film Crystallization via High-Boiling-Point Additives
Innovation 3: Mixed Solvents Compatible with the Narrow Bandgap PCBTDPP System
Innovation 4: Solvent annealing–specific optimization for large-area devices
Innovation 5: Wide viscosity compatibility and long-term printing stability
IV. Existing Technical Challenges and the Breakthrough Solutions Proposed in This Paper
Challenge 1: Single low-boiling-point solvent droplets evaporate rapidly during flight, leaving a thin film riddled with particle defects.
Problem: Solvents with boiling points below 180°C are unsuitable for aerosol‑based processing, and pure DCB–printed films exhibit micron‑scale surface roughness, resulting in a device efficiency of only 1.20%.
✅ Solution: The primary solvent is paired with 1,8-octanedithiol, which has an exceptionally high boiling point of 270°C, to slow down droplet evaporation, prevent premature solute precipitation, and ensure a smooth, particle-free thin film surface.
Challenge 2: The coffee-ring effect results in excessively thick and non-uniform edge regions of the thin film.
Problem: During the drying of single-component inks, radial flow transports solutes toward the edges, leading to significant variations in film thickness and resulting in performance variability across large-area devices.
✅ Solution: Employ a blended solvent system to modulate the solvent evaporation gradient, suppress internal convection within the droplets, and enhance film uniformity.
Challenge 3: High-temperature thermal annealing disrupts the native morphology of aerosols.
Issue: Post‑printing high‑temperature annealing induces excessive fullerene aggregation, disrupts phase separation, increases series resistance, and degrades device performance.
✅ Solution: Select post‑processing strategies based on the polymer system: the P3HT system requires no annealing; the PCBTDPP system employs mild solvent‑vapor annealing, with no high‑temperature steps throughout.
Challenge 4: Poor compatibility between narrow‑band polymers and high‑boiling‑point additives.
Problem: The solubility of PCBTDPP plummets in long-chain, high-boiling-point additives, leading to phase-separation defects in the thin film.
✅ Solution: Abandon high-boiling-point additives and adopt a DCB/chlorobenzene mixed solvent to balance dissolution and drying rates, thereby optimizing both film morphology and light absorption.
Challenge 5: Printing efficiency drops significantly over large areas.
Problem: The morphology of small-area samples is easy to control, but when the area is scaled up to 1 cm², the leakage current increases and the fill factor decreases.
✅ Solution: Optimize the printing travel speed and employ multi-layer stacking, combined with solvent vapor annealing to reconstruct charge transport pathways, thereby narrowing the efficiency gap between small- and large-scale devices.
V. Future Application Prospects of Aerosol-Printed Organic Photovoltaics
1. Flexible wearable photovoltaic devices
2. Building-integrated curved photovoltaic systems
3. Low-cost, large-area roll-to-roll mass production
4. Expansion of Layered Organic Photovoltaics
5. Specialized Micro-Optoelectronic Devices
Figure 1. Schematic diagram of aerosol jet printing, the chemical structures of the materials used in the experiment, and the device architecture. An aerosol generated by ultrasonic treatment of a solution is conveyed from above into the print head under the propulsion of nitrogen (N₂); a sheath gas is introduced laterally into the print head, enveloping the atomized microdroplets to form a fine stream. As numerous microdroplets coalesce, they give rise to a thin liquid film, which subsequently dries on the substrate surface to yield a solid thin film.
Figure 2. Optical microscopy images of thin films fabricated by aerosol jet printing, using: (a) dichlorobenzene; (b) a mixture of dichlorobenzene and 1,8-diiodooctane (at 2 vol %); and (c) a mixture of dichlorobenzene and 1-chlonaphthalene (at 5 vol %). The black dots represent particulate protrusions on the film surface, with dimensions of approximately 1 μm, consistent with the size of microdroplets in the atomizing gas. Scale bar: 10 μm.
Figure 3. Absorption spectra of P3HT:PC60BM blend films prepared by aerosol jet printing (hollow circles indicate the case with DCB as an additive; solid lines indicate the case with 1,8-octanedithiol added at a volume fraction of 2%).
Figure 4. J–V curves of a P3HT:PC60BM device fabricated by printing from a DCB solution, with 1,8-octanedithiol added at a volume fraction of 2%, under AM1.5G illumination (100 mW/cm²). The inset shows an optical microscopy image of the printed film, with a scale bar of 10 μm.
Figure 5. UV–vis absorption spectra of PCB-TDPP in CB and DCB solutions, as well as in thin films prepared by aerosol jet printing from CB- and DCB-based polymer solutions. The polymer concentration in the solutions is 11 μg/mL.
Figure 6. J–V curves of PCBTDP:PC70BM devices with solvent‑annealed active layers under AM1.5G illumination (100 mW/cm²). The inset shows an optical microscope image of the film, with a scale bar of 10 μm.
Table 2. Summary of Typical Device Characteristics for PCBTDP:PC70BM Devices with Active Layers Printed Using Different Solutions, with or without Solvent Annealing
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