Correlating crystalline structure with charge mobility in conjugated statistical copolymers for field-effect transistors

Abstract

Since thiophene and selenophene have comparable molecular structures and possess individual remarkable optoelectronic characteristics, crystals comprising both units may exhibit improved charge mobility than their respective homopolymers due to the synergy. This, however, has yet to be largely utilized in statistical copolymers. In this study, a series of poly(3-butylthiophene)-stat-poly(3-hexylselenophene) (P3BT-stat-P3HS) statistical copolymers with variable molar ratios of thiophene to selenophene were synthesized and investigated in respect of thermal, crystalline, and charge transport properties. All three P3BT-stat-P3HS copolymers were found to well crystallize in an edge-on configuration in spite of their random arrangement of thiophene and selenophene units along the main backbones. Consequently, high-performance organic field-effect transistors (OFETs) were achieved in as-cast P3BT-stat-P3HS crystals, surpassing those of P3BT, P3HS and P3BT/P3HS blend. After 150 °C thermal annealing, the charge mobilities of these statistical copolymers were further slightly enhanced due to the improved crystallinities as well as more ordered crystalline structures. This work shows the improved field-effect mobilities in conjugated polymer-based statistical copolymers due to the synergy of thiophene and selenophene units. Such P3BT-stat-P3HS crystals may be used in diverse printable flexible electronics owing to their excellent charge mobilities and annealing-free properties.