Synthesis and Properties of Alternating Copolymers Based on 4H-Cyclopenta[2,1-b:3,4-b']dithiophene and 4H-Dithieno[3,2-b:2',3'-d]silol

A number of copolymers based on 4H-cyclopenta[2,1-b:3,4-b']dithiophene and 4H-dithieno[3,2-b:2',3'-d]silol are synthesized via direct С–Н arylation and Suzuki cross-coupling, and their properties are compared. The chemical structure of the copolymers is investigated by ¹Н and ¹³С NMR spectroscopy, and their molecular-mass characteristics are determined by GPC. The study of absorption spectra of the copolymers in dilute solutions and thin films shows that they absorb light in a wide visible spectral range (300–800 nm). On the basis of the cyclic voltammetry data, the levels of boundary molecular orbitals—the highest occupied and the lowest unoccupied—are estimated and the width of the energy gap is shown to be in the range of 1.4–1.9 eV. Using the copolymers as donor components of the active layer, the samples of solar photocells are manufactured and their photovoltaic properties are investigated.