Photocurrent Saturation Mechanisms in Colloidal Quantum Dot Photodetectors

Area of Science:

• Optoelectronics
• Materials Science
• Nanotechnology

Background:

• Colloidal quantum dot photodiodes (QDPDs) are promising for infrared sensing, offering high detectivity and fast response times.
• A key limitation of QDPDs is their restricted linear dynamic range (LDR), where photocurrent saturates at moderate light intensities.

Purpose of the Study:

• To investigate the bottleneck limiting the linear dynamic range in lead sulfide (PbS)-based QDPDs.
• To identify the charge carrier dynamics responsible for photocurrent saturation in QDPDs.

Main Methods:

• Operando transient absorption spectroscopy was employed to study carrier recombination in QDPDs.
• Kinetic Monte Carlo simulations were used to model charge carrier behavior and loss pathways.

Main Results:

• Charge carrier recombination is significantly faster in QDPD films and device stacks compared to isolated quantum dots.
• Trion recombination, influenced by hopping and doping-induced charges, was identified as a major loss pathway.
• Photocurrent saturation occurs when trion recombination rates match charge separation rates.

Conclusions:

• The limited LDR in QDPDs is primarily due to accelerated recombination pathways.
• Variations in reported LDR values in literature likely stem from differing carrier extraction efficiencies.
• Enhancing carrier extraction rates is crucial for extending the linear dynamic range of QDPDs.