Influence of Selenium on the Optoelectronic Properties of a Series of Structurally Simple p-type Polymers for Organic Thin-Film Transistors

Tremendous efforts have been dedicated to improving the performance of organic thin-film transistors (OTFTs) through careful polymer design. Sulfur-containing polymers have been studied in-depth; however, their selenium-containing analogs remain rarer. Herein, a series of polymers of low synthetic complexity with systematically increasing selenium content are presented. Three novel polymers FO6-Se, FO6-BS-T, and FO6-BS-Se are synthesized using a facile two-step protocol, combining combinations of selenophene, thiophene, benzothiadiazole (BT), and benzoselenadiazole (BS) units. The optical, electrochemical, and morphological properties of these polymers are comprehensively analyzed, revealing interesting structure-property relationships. Results show a significant bathochromic shift in absorption and emission spectra upon increasing Se content. Charge transport properties are evaluated in OTFTs, with FO6-BS-T exhibiting the highest hole mobility of 0.038 cm²V⁻¹s⁻¹ when annealed at 100 °C. Grazing-incidence wide-angle X-ray scattering (GIWAXS) studies reveal reduced crystallinity upon BS incorporation and density functional theory (DFT) calculations indicate increased backbone twisting upon BS inclusion compared to BT. This work demonstrates how systematic selenium incorporation alters polymer properties, particularly frontier molecular levels, and morphology, contributing to the understanding of selenium-containing scalable polymers for potential application in organic thin-film transistors.