Ladder-type heteroacenepolymers bearing carbazole and thiophene ring units and their use in field-effect transistors and photovoltaic cells

Abstract

A family of ladder-type π-excessive conjugated monomer (dicyclopentathienocarbazole (DCPTCz)) integrating the structural components of carbazole and thiophene into a single molecular entity is synthesized and polymerized by oxidative coupling to yield poly(dicyclopentathienocarbazole) (PDCPTCz). Moreover, through the careful selection of 2,1,3-benzothiadiazole unit as a π-deficient building block, the dicyclopentathienocarbazole-based donor–acceptor copolymer (poly(dicyclopentathienocarbazole-alt-2,1,3-benzothiadiazole) (PDCPTCz-BT)) is prepared by Suzuki polycondensation. The optical, electrochemical, and field-effect charge transport properties of the resulting polymers (PDCPTCz and PDCPTCz-BT) are not only characterized in detail but also their bulk-heterojunction (BHJ) solar cell in combination with PC₇₁BM are evaluated. The values of field-effect mobility (µ) for PDCPTCz and PDCPTCz-BT are 8.7 × 10⁻⁶ cm² V⁻¹s⁻¹ and 2.7 × 10⁻⁴ cm² V⁻¹s⁻¹, respectively. A power conversion efficiency (PCE) of 1.57% is achieved on the PDCPTCz-BT/PC₇₁BM device, implying that the push–pull copolymers based on ladder-type dicyclopentathienocarbazole as an electron-donating moiety are promising for organic electronic devices.