Switching from Electron to Hole Transport in Solution-Processed Organic Blend Field-Effect Transistors

Area of Science:

• Organic electronics
• Materials science
• Semiconductor physics

Background:

• Organic semiconductors offer solution processability and large-area manufacturing advantages for electronic devices.
• Bulk heterojunctions (BHJ), blends of organic semiconductors, enable diverse applications like transistors, LEDs, and sensors.
• Controlling charge carrier transport in BHJ films is crucial for optimizing device performance.

Purpose of the Study:

• To investigate the influence of processing and post-treatment on charge carrier transport in BHJ films.
• To understand how thin film morphology affects the transition from electron to hole domination.
• To optimize BHJ film morphology for specific charge transport characteristics.

Main Methods:

• Fabrication of BHJ films using spin-coating of n-type PDI8-CN2 and p-type PBTTT-C14 blends.
• Systematic investigation of processing parameters: rotation speed, solution temperature, and thermal annealing.
• Morphological characterization using atomic force microscopy (AFM), scanning electron microscopy (SEM), and grazing incidence wide-angle X-ray scattering (GWAXS).

Main Results:

• Processing and thermal annealing were found to switch charge carrier transport from electron to hole domination.
• Thermal annealing induced a morphological transition from small, interconnected PDI8-CN2 crystals to large, planar PDI8-CN2 domains on the film surface.
• Morphological changes directly correlated with the observed shift in charge carrier transport dominance.

Conclusions:

• Thermal annealing is an effective post-treatment method to control BHJ morphology and dictate charge carrier transport.
• The study demonstrates a pathway to tune the electronic properties of organic BHJ films for specific applications.
• This work contributes to the advancement of solution-processed organic electronics, particularly for field-effect transistors.