The Future of Fast & Affordable Infrared Sensors: Fully Printed PbS Nanocrystal Photodetectors

In the world of advanced electronics, the ability to "print" complex sensors is a game-changer for reducing costs and scaling production. A breakthrough study published in ACS Nano by YousefiAmin et al. demonstrates a significant leap forward: fully printed infrared photodetectors that are not only high-performing but also remarkably cheap and fast to manufacture.
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Why Printed Infrared Detectors Matter

Traditional infrared (IR) sensors often rely on expensive materials and complex manufacturing processes like optical lithography. This study introduces a method to create highly sensitive IR detectors using colloidal PbS (Lead Sulfide) nanocrystals through automated printing.

Key benefits of this approach include:

  • Ultra-Low Cost: Material consumption is less than 0.3 mg per detector, costing below 20 cents per square centimeter.

  • High-Speed Manufacturing: The automated printing process takes only 14 seconds per detector.

  • Exceptional Sensitivity: These devices achieve a specific detectivity ($D^*$) of $\sim10^{12}$ cm $Hz^{1/2}/W$, putting them on par with state-of-the-art IR photodetectors.

The Technology: Engineering the "Functional Ink"

The core innovation lies in the development of a specialized electronic ink. Standard PbS nanocrystals are typically capped with insulating oleic acid, which blocks electrical current.

To make them "printable" and conductive, the researchers:

  1. Replaced Ligands: They swapped oleic acid for perovskite-like methylammonium iodobismuthate ligands, which facilitate efficient charge transport.

  2. Optimized Solvents: A ternary solvent mixture (DMF/NMF/DMSO) was used to ensure smooth film formation and prevent cracking during drying.

  3. Added Polymers: By adding poly(vinylpyrrolidone) (PVP), the team improved the ink’s stability and eliminated the "fractal crack patterns" that usually ruin printed films.

Two Paths to a Fully Printed Device

The researchers explored two different printing architectures:

FeatureApproach (i): All-InkjetApproach (ii): Robot & 3D Printing
Method

Layer-by-layer inkjet printing.

 

3D-printed ABS frame + robotic droplet dispenser.

 

Speed

Relatively slow (3 mins per detector).

 

 

Extremely fast (14 seconds per detector).

 

Performance

Functional, but prone to nozzle clogging.

 

 

Superior stability, high detectivity, and scalable.

 


The final devices utilize printed silver (Ag) electrodes and a ZnO (Zinc Oxide) interlayer to prevent corrosion and reduce dark current, ensuring the sensors are both durable and accurate.

What’s Next?

While these specific sensors are designed for infrared detection, the "PVP-modified ink" strategy is expected to work for a wide range of materials. This paves the way for the low-cost production of solar cells, thin-film transistors, and wearable health monitors.

  • Source: YousefiAmin, A., et al. (2019). Fully Printed Infrared Photodetectors from PbS Nanocrystals with Perovskite Ligands. ACS Nano, 13(2), 2389-2397. [DOI: 10.1021/acsnano.8b09223]