Fluorinated benzothiadiazole (BT) groups as a powerful unit for high-performance electron-transporting polymers

Area of Science:

• Materials Science
• Organic Electronics
• Polymer Chemistry

Background:

• Polymer solar cells (PSCs) have seen significant advances with fluorinated 2,1,3-benzothiadiazole (BT)-based polymers.
• These materials offer improved power conversion efficiency, but their charge-transport characteristics require further investigation.

Purpose of the Study:

• To synthesize and investigate new diketopyrrolopyrrole (DPP)-based polymers with single- and double-fluorinated BT units.
• To assess the influence of fluorinated BT units on charge-transport properties in organic field-effect transistors (OFETs).

Main Methods:

• Synthesis of PDPP-FBT and PDPP-2FBT polymers incorporating DPP and fluorinated BT units.
• Characterization using UV-Vis spectroscopy, cyclic voltammetry, and grazing incidence X-ray diffraction (GIXD).
• Charge-transport measurements in organic field-effect transistors (OFETs).

Main Results:

• The introduction of double-fluorinated BT (PDPP-2FBT) altered optical profiles and energy levels, resulting in a wider bandgap and deeper HOMO compared to PDPP-FBT and PDPP-BT.
• Both fluorinated polymers exhibited semicrystalline lamellar structures with edge-on orientations.
• Electron mobilities reached up to 0.42 cm² V⁻¹ s⁻¹ (PDPP-FBT) and 0.30 cm² V⁻¹ s⁻¹ (PDPP-2FBT), while hole mobilities remained above 0.1 cm² V⁻¹ s⁻¹.

Conclusions:

• Fluorinated BT blocks are a promising strategy for enhancing electron transport in polymers.
• This approach improves electron mobility in OFETs without negatively impacting hole mobility.
• The findings contribute to the molecular design of high-performance organic electronic materials.