Synthesis and Photovoltaic Properties of Silole-Containing Conjugated Polymers

Siloles are a group of five-membered silacyclics that possess a unique low-lying LUMO level associated with sigma*-pi* conjugation. Siloles exhibit high electron acceptability, unusual aggregation-induced emission (AIE) and have been utilized as light-emitting layers in the fabrication of electroluminescence devices. The incorporation of 2,3,4,5-tetraarylsiloles into the main chain of polymers is of interest and importance in chemistry and functionalities. Some optoelectronic properties, impossible for silole small molecules, may be realized with silole-containing polymers. In this paper, four donor-acceptor (D-A) conjugated polymers with electron-withdrawing silole units and electron-donating fluorene or silafluorene units have been synthesized and characterized by NMR, TGA, GPC, and elemental analysis measurement. The photophysical properties show that all the polymers exhibit broad absorption range covering the whole UV-vis spectral region of the sunlight. The HOMO energy levels of four polymers are lower than -5.2 eV and the LUMO energy levels of them are higher than -3.6 eV, so these polymers are promising candidates for the effective applications of polymer solar cells (PSCs). Therefore, the photovoltaic properties of the polymer as donor was investigated by fabricating the bulk-heterojunction (BHJ) solar cells with a typical structure of ITO/PEDOT:PSS/polymer:PC61BM/Al. As a preliminary result, the BHJ devices based on PF-HSTBT, PF-HOSTBT, PSiF-HSTBT, and PSiF-HOSTBT showed the power conversion efficiencies (PCEs) of 1.18%, 0.62%, 1.2%, and 0.83%, respectively. The short-circuit current density (J(sc)) and PCE values of PSCs based on PF-HSTBT and PSiF-HSTBT are higher than those of PF-HOSTBT and PSiF-HOSTBT because of the reduced steric hindrance and improved structural planarity.