Enhanced Infrared Photodiodes Based on PbS/PbCl Core/Shell Nanocrystals

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Colloidal lead sulfide (PbS) nanocrystals are crucial for infrared photodetectors.
• Large-diameter nanocrystals present complex surface structures that hinder device performance.
• Effective passivation is essential for advancing short-wave infrared (SWIR) photodetector technology.

Purpose of the Study:

• To compare the performance of SWIR photodiodes fabricated with PbS/PbCl (core/shell) nanocrystals versus PbS-only (core) nanocrystals.
• To investigate the impact of shell chemistry on device performance by evaluating energy level offsets and interfacial chemistry.
• To elucidate the reasons for performance disparities between core-only and core/shell nanocrystal devices.

Main Methods:

• Fabrication and direct comparison of SWIR photodiodes using core/shell and core-only PbS nanocrystals.
• Evaluation of thickness-dependent energy level offsets between nanocrystal films and zinc oxide electron-transport layers.
• Analysis of interfacial chemistry, including native organic ligand removal and interface dipole formation.

Main Results:

• Core/shell devices exhibited significantly higher external quantum efficiencies and lower dark current densities compared to PbS-only devices.
• PbS-only devices suffered from shunting and inefficient charge extraction.
• Performance differences were attributed to unfavorable interface dipole formation and surface defect states in core-only films due to inadequate ligand removal.

Conclusions:

• The PbS/PbCl core/shell system provides a superior passivation strategy for large-diameter nanocrystals.
• This approach effectively manages nonpolar (100) surface facets that are poorly passivated by conventional halide treatments.
• Core/shell nanocrystals offer a promising route for developing high-performance SWIR photodetectors.