Switching charge-transfer characteristics from p-type to n-type through molecular "doping" (co-crystallization)

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Chemistry

Background:

• Organic semiconductors' charge transport is crucial for electronic devices.
• Tuning semiconductor properties often relies on molecular design or processing.
• Analogy to silicon industry's heteroatom implantation suggests molecular doping for organic materials.

Purpose of the Study:

• To investigate molecular doping (co-crystallization) as a method to switch charge transport in organic semiconductors.
• To synthesize and characterize a novel organic semiconductor and its doped complex.
• To explore the structural and electronic implications of co-crystallization.

Main Methods:

• Synthesis of 2,7-di-tert-butyl-10,14-di(thiophen-2-yl)phenanthro[4,5-abc][1,2,5]thiadiazolo[3,4-i]phenazine (DTPTP).
• Co-crystallization of DTPTP with tetracyanoquinodimethane (TCNQ).
• Single crystal X-ray diffraction analysis.
• Charge transport measurements.
• Theoretical electronic structure calculations.

Main Results:

• The pristine DTPTP exhibits p-type semiconductor behavior (0.3 cm² V⁻¹ s⁻¹).
• Co-crystallization with TCNQ (forming DTPTP₂-TCNQ) switches the material to n-type (3 × 10⁻³ cm² V⁻¹ s⁻¹ in air).
• X-ray studies reveal a 1D mixed π-π stacking in DTPTP₂-TCNQ, distinct from DTPTP's herringbone packing.
• Theoretical analysis indicates a quasi-2D electron transport network in the doped system.

Conclusions:

• Molecular doping via co-crystallization is a viable strategy to switch charge transport characteristics of organic semiconductors.
• The DTPTP/TCNQ system demonstrates a novel host-guest co-crystal engineering approach.
• This work provides a new pathway for designing organic electronic materials with tunable properties.