Surface Ligand Engineering for a Lead-Free Cs₃Cu₂Br₅ Microcrystal-Based Humidity Sensor with a Giant Response.

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Traditional lead-based halide perovskites show promise for humidity sensing but suffer from instability and lead toxicity.
• Developing lead-free, stable perovskite materials is crucial for practical environmental sensing applications.

Purpose of the Study:

• To develop an environmentally friendly humidity sensor using lead-free Cs3Cu2Br5 perovskite microcrystals.
• To investigate the impact of surface ligands (OLA and OAm) on the humidity sensing performance.

Main Methods:

• Preparation of lead-free Cs3Cu2Br5 perovskite microcrystals passivated with oleic acid (OLA) and oleylamine (OAm).
• Fabrication of humidity sensors using the passivated perovskite microcrystals.
• Testing and analysis of sensor performance across a range of relative humidity (RH) levels (12-95%).

Main Results:

• Humidity sensors exhibited significant impedance variations: 10^6 Ω for OLA and 10^5 Ω for OAm.
• Both OLA and OAm passivated sensors demonstrated excellent repeatability, low hysteresis, and good stability.
• OLA promoted porous films with high water absorption, enhancing responsiveness, while OAm formed dense films, improving low humidity response.

Conclusions:

• Lead-free Cs3Cu2Br5 perovskite microcrystals are viable for eco-friendly humidity sensing.
• Surface ligand engineering (OLA vs. OAm) allows tuning of sensor properties like responsiveness and response/recovery times.
• OLA enhances overall responsiveness due to hydrophilicity and film porosity, whereas OAm improves low-humidity performance and speed.