Elementary steps in electrical doping of organic semiconductors

Area of Science:

• Organic electronics
• Semiconductor physics

Background:

• Fermi level control via doping is fundamental in inorganic semiconductors and applied to organic semiconductors.
• Molecular doping in organic semiconductors, crucial for OLEDs, remains poorly understood, with empirical material design and debated elementary steps.

Purpose of the Study:

• To quantitatively investigate the mechanism of molecular doping in organic semiconductors.
• To resolve the discrepancy between efficient carrier release and the presumed large Coulomb barrier.

Main Methods:

• Modeling doping as a two-step process: single-electron transfer and subsequent dissociation of the integer-charge transfer complex (ICTC).
• Incorporating energetic disorder into the semiconductor model.

Main Results:

• Carrier release via ICTC dissociation has a low activation energy (tens of meV) despite high Coulomb binding energy (hundreds of meV).
• Energetic disorder is key to overcoming the Coulomb barrier.
• The extended semiconductor model explains the observed doping behavior, including the reserve regime.

Conclusions:

• Molecular doping is a two-step process involving ICTC dissociation, significantly influenced by energetic disorder.
• This work provides a quantitative understanding of carrier release in doped organic semiconductors.
• The findings offer a basis for improved, rational material design in organic electronics.