A Low-Bandgap Semiconducting Polymer for Photovoltaic Devices and Infrared Emitting Diodes

A novel low-bandgap conjugated polymer (PTPTB, Eg=~1.6 eV), consisting of alternating electron-rich N-dodecyl-2,5-bis(2'-thienyl)pyrrole (TPT) and electron-deficient 2,1,3-benzothiadiazole (B) units, is introduced for thin-film optoelectronic devices working in the near infrared (NIR). Bulk heterojunction photovoltaic cells from solid-state composite films of PTPTB with the soluble fullerene derivative [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as an active layer shows promising power conversion efficiencies up to 1 % under AM1.5 illumination. Furthermore, electroluminescent devices (light-emitting diodes) from thin films of pristine PTPTB show near infrared emission peaking at 800 nm with a turn on voltage below 4 V. The electro luminescence can be significantly enhanced by sensitization of this material with a wide bandgap material such as the poly(p-phenylene vinylene) derivative MDMO-PPV.