Quantifying the Localization of Charges Generated upon Molecular Doping of Conjugated Polymers

Area of Science:

• Materials Science
• Organic Electronics
• Semiconductor Physics

Background:

• Understanding charge carrier states (localized vs. mobile) is crucial for organic semiconductor doping mechanisms.
• Quantifying these states typically requires complex Hall effect measurements or specialized equipment.
• Molecular doping is a key technique for tuning organic semiconductor properties.

Purpose of the Study:

• To develop and validate a straightforward method for quantifying mobile and localized charge concentrations in molecularly doped conjugated polymers.
• To compare charge transport characteristics in two different polymer systems doped with F4TCNQ.
• To provide explicit parameters governing charge transport, including carrier concentration, mobility, and mobile fraction.

Main Methods:

• Spectroelectrochemical calibration was employed to quantify mobile and localized charge concentrations.
• Results were cross-validated using X-ray photoemission spectroscopy and Hall effect measurements.
• Established transport models, including the semilocalized transport (SLoT) model, were fitted to the data.

Main Results:

• In poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), only ~10% of carriers became mobile at high doping levels.
• In the (poly(bithiophene-thienothiophene) derivative modified with a triethylene glycol side chain (Pg2T-TT), over 50% of carriers were mobile at similar doping levels.
• SLoT model fitting indicated delocalized transport in Pg2T-TT and localized transport in PBTTT.

Conclusions:

• Spectroelectrochemical calibration offers a direct platform for quantifying charge localization in doped conjugated polymers.
• The polymer structure significantly influences the mobile fraction of charge carriers after molecular doping.
• This work provides essential parameters for understanding and optimizing charge transport in organic electronic devices.