A solution-processed tin dioxide film applicable as a transparent and flexible humidity sensor

Area of Science:

• Materials Science
• Nanotechnology
• Sensor Technology

Background:

• Developing efficient and cost-effective humidity sensors is crucial for environmental monitoring and industrial applications.
• Transparent and flexible humidity sensors are highly desirable for wearable electronics and smart windows.

Purpose of the Study:

• To develop an all-solution-processed, template-free transparent tin oxide humidity sensor on both rigid and flexible substrates.
• To investigate the effect of hot water treatment (HWT) on the sensing properties of tin oxide films.
• To elucidate the mechanism behind the humidity-sensing behavior.

Main Methods:

• Fabrication of transparent tin oxide (SnO₂) films on borosilicate glass and polyethylene terephthalate (PET) substrates using a spin-spray process.
• Post-deposition treatment using hot water treatment (HWT) at 100 °C.
• Characterization of film resistivity, semiconductor properties, and humidity sensing performance (sensitivity, response/recovery time).

Main Results:

• As-prepared SnO₂ films were insulators, but HWT transformed them into semiconductors with significantly reduced resistivity.
• Humidity sensitivity increased dramatically with increasing relative humidity (RH), with a 35.2-fold and 3.5-fold increase for glass and PET substrates, respectively, at 95% RH compared to 5% RH.
• The sensing mechanism was attributed to the formation of a hydroxyl layer and tin hydroxyl derivatives, providing mobile protons that respond to humidity changes.

Conclusions:

• The developed all-solution-processed SnO₂-based humidity sensors exhibit excellent sensing performance and potential for transparent and flexible applications.
• HWT is a critical step for activating the semiconductor properties and enabling humidity sensing.
• The proton conductivity mechanism offers a promising pathway for future humidity sensor development.