Achieving a good life time in a vertical-organic-diode gas sensor

Area of Science:

• Organic electronics
• Chemical sensing
• Materials science

Background:

• Development of sensitive and air-stable gas sensors is crucial for environmental monitoring and industrial safety.
• Polythiophene-based diodes offer potential for low-cost gas sensing applications.
• Achieving long-term stability in ambient conditions remains a challenge for organic semiconductor sensors.

Purpose of the Study:

• To investigate the factors enabling sensitive ammonia detection with high air stability using a novel polythiophene diode architecture.
• To compare the performance and stability of two different polythiophene materials, P3HT and PQT-12, as active sensing layers.
• To demonstrate an improved storage lifetime for organic semiconductor-based gas sensors.

Main Methods:

• Fabrication of low-cost polythiophene diodes with a vertical channel and porous top electrode.
• Evaluation of poly(3-hexylthiophene) (P3HT) and poly(5,5'-bis(3-dodecyl-2-thienyl)-2,2'-bithiophene) (PQT-12) as active sensing layers.
• Two-dimensional current simulation to analyze device physics, specifically vertical nanometer junctions (VNJ).
• Ammonia sensing experiments to determine detection limits and assess air stability over time.

Main Results:

• The proposed device architecture, utilizing vertical nanometer junctions (VNJ), enables sensitive ammonia detection for both P3HT and PQT-12 diodes.
• Both PQT-12 and P3HT VNJ-diodes achieved a detection limit of 50-ppb ammonia due to de-doping reactions with ammonia molecules.
• The P3HT VNJ-diode lost stability after two days of air storage, while the PQT-12 VNJ-diode maintained its response to ammonia after 25 days of air storage.

Conclusions:

• The PQT-12 polythiophene material, when incorporated into a vertical channel diode structure, provides a pathway to highly stable and sensitive ammonia sensors.
• The VNJ architecture in polythiophene diodes is key to achieving low detection limits for ammonia.
• This study successfully demonstrates a significant improvement in the air storage lifetime of organic semiconductor-based gas sensors, paving the way for practical applications.