Surface versus Bulk Currents and Ionic Space-Charge Effects in CsPbBr₃ Single Crystals.

Area of Science:

• Materials Science
• Solid-State Physics
• Device Physics

Background:

• Cesium lead bromide (CsPbBr3) single crystals possess excellent optoelectronic properties for ionizing-radiation detection.
• However, their mixed ionic-electronic conductivity leads to instability and hysteresis, limiting device longevity.

Purpose of the Study:

• To electrically characterize CsPbBr3 single crystals over extended operational periods (hours).
• To elucidate the transport mechanisms, including bulk and surface contributions, and their impact on device performance.

Main Methods:

• Fast time-of-flight measurements to determine bulk mobilities.
• Guard ring (GR) configuration to differentiate bulk and surface transport.
• Current transients and impedance spectroscopy to analyze space-charge-limited current (SCLC) regimes.

Main Results:

• Bulk mobilities of 13-26 cm2 V-1 s-1 were measured, exhibiting negative voltage bias dependency.
• Significant differences in transport properties were observed between bulk and surface regions using the GR method.
• Evidence suggests Poole-Frenkel-like mechanisms and ionic-SCLC as dominant transport modes.

Conclusions:

• Ionic-SCLC appears to be a critical operational mode in CsPbBr3 devices, even when ionic contributions seem minimal.
• Understanding these transport mechanisms is crucial for mitigating instability and improving long-term device operation in radiation detectors.