Bulk charge carrier transport in push-pull type organic semiconductor.

Area of Science:

• Organic electronics
• Materials science
• Solid-state physics

Background:

• Charge transport properties, particularly charge carrier mobility, are key metrics for organic electronic and optoelectronic devices.
• Mobility is influenced by molecular structure, crystal packing, and film fabrication methods, affecting anisotropy and order.
• The study focuses on a highly efficient small-molecule organic semiconductor with a push-pull structure.

Purpose of the Study:

• To investigate the charge transport properties, molecular packing, and film morphology of a specific organic semiconductor.
• To understand the relationship between structural phases and charge carrier mobility.
• To provide insights for developing advanced organic photovoltaic materials and devices.

Main Methods:

• Time-of-flight (TOF) technique to measure charge carrier mobility.
• Grazing incidence X-ray diffraction (GIXRD) to analyze molecular packing and film morphology.
• Investigation of different structural phases (isotropic and polycrystalline) and their impact on transport properties.

Main Results:

• In the isotropic phase, the material exhibits ambipolar charge transport with mobilities of 1.0 × 10(-3) cm(2)/(V s) (electron) and 6.5 × 10(-4) cm(2)/(V s) (hole) at 210.78 °C.
• Crystallization into an anisotropic triclinic phase below 210 °C increases hole mobility by tenfold, limited by side-chain interactions.
• Faster cooling below 90 °C results in more isotropic crystalline domains, yielding higher hole mobilities up to 2 × 10(-2) cm(2)/(V s) at 25 °C.

Conclusions:

• Film fabrication and resulting structural order significantly impact charge carrier mobility in organic semiconductors.
• Understanding structure-property relationships is crucial for optimizing performance in organic photovoltaic devices.
• The findings guide the design of new organic semiconductor materials with enhanced charge transport characteristics.