Space charge limited current measurements on conjugated polymer films using conductive atomic force microscopy

Area of Science:

• Materials Science
• Organic Electronics
• Nanotechnology

Background:

• Conjugated polymers are vital for organic electronic devices, including thin-film transistors and solar cells.
• Accurate characterization of charge carrier mobility is essential for optimizing device performance.
• Conductive atomic force microscopy (c-AFM) offers high-resolution measurements but can lead to mobility overestimation.

Purpose of the Study:

• To develop a method for accurate, local measurements of charge carrier mobility in conjugated polymer films.
• To address the discrepancy between c-AFM and macroscopic device measurements of mobility.
• To provide a reliable approach for extracting charge carrier mobility in organic semiconductors.

Main Methods:

• Measurement of space charge limited currents (SCLC) using c-AFM and macroscopic diodes.
• Application of the Mott-Gurney law for mobility estimation.
• Finite element simulations to model tip-sample geometry in c-AFM.
• Development and application of a semiempirical scaling factor for c-AFM data correction.

Main Results:

• c-AFM measurements showed significantly higher current densities than planar devices.
• Standard Mott-Gurney analysis of c-AFM data overestimated mobility by up to three orders of magnitude.
• Finite element simulations revealed the impact of tip-sample geometry on current measurements.
• A corrected method using a scaling factor yielded mobility values consistent with planar devices.

Conclusions:

• The proposed method accurately quantifies charge carrier mobility in conjugated polymers using c-AFM.
• Accounting for tip-sample geometry is critical for reliable c-AFM-based mobility measurements.
• This work enables more precise characterization of organic semiconductor materials for advanced electronic applications.