Synthesis of Thiophene-Based π-Conjugated Polymers Containing Oxadiazole or Thiadiazole Moieties and Their Application to Organic Photovoltaics

Abstract

We report the synthesis, properties, and photovoltaic applications of new π-conjugated polymers having thiophene, 3,4-dihexylthiophene, and 1,3,4-oxadiazole (OXD) or 1,3,4-thiadiazole (TD) units in the main chain, denoted as P1 and P2. They were synthesized by the Stille coupling reaction of 2,5-bis(trimethylstannyl)thiophene and the corresponding monomers of 2,5-bis(5′-bromo-3′,4′-dihexylthien-2′-yl)-1,3,4-oxadiazole or 2,5-bis(5′-bromo-3′,4′-dihexylthien-2′-yl)-1,3,4-thiadiazole, respectively. The experimental results indicated that the introduction of an electron-accepting moiety of OXD or TD lowered the highest occupied molecular orbital (HOMO) energy levels, resulting in the higher the open-circuit voltage (Voc) values of polymer solar cells (PSCs). Indeed, the PSCs of P1 and P2 showed high Voc values in the range 0.80–0.90 V. The highest field-effect transistor (FET) mobilities of P1 and P2 with the OXD and TD moieties, respectively, were 1.41 × 10–3 and 8.81 × 10–2 cm2 V–1 s–1. The higher mobility ...