Transient photocurrent in molecular junctions: singlet switching on and triplet blocking

Area of Science:

• Molecular electronics
• Photochemistry
• Quantum mechanics

Background:

• Understanding charge transport in molecular junctions is crucial for developing novel electronic devices.
• Photochromic molecules offer unique light-responsive properties for optoelectronic applications.

Purpose of the Study:

• To analyze the photocurrent of photochromic molecules under moderate light intensity using a kinetic approach.
• To derive analytical expressions for transient and steady-state current components.

Main Methods:

• Utilized a kinetic approach for charge transmission analysis in molecular junctions.
• Employed the Highest Occupied Molecular Orbital-Lowest Unoccupied Molecular Orbital (HOMO-LUMO) model for single-electron molecular states.
• Derived analytical expressions for sequential (hopping) and direct (tunnel) current components.

Main Results:

• Derived expressions for transient and steady-state photocurrent components.
• Identified conditions for achieving maximal current component values.
• Demonstrated the possibility of a large, peak-like transient switch-on photocurrent.

Conclusions:

• The kinetic approach provides insights into photocurrent behavior in photochromic molecular junctions.
• A significant transient photocurrent can arise when charge transmission rates are slower than excitation/de-excitation rates and triplet states act as traps.