Conjugated polymers based on C, Si and N-bridged dithiophene and thienopyrroledione units: synthesis, field-effect transistors and bulk heterojunction polymer solar cells

A series of low band-gap conjugated polymers (PDTC, PDTSi and PDTP) containing electron-rich C-, Si-, and N-bridged bithiophene and electron-deficient thienopyrroledione units were synthesized via Stille coupling polymerization. All these polymers possess a low-lying energy level for the highest occupied molecular orbital (HOMO) (as low as -5.44 eV). As a result, photovoltaic devices derived from these polymers show high open circuit voltage (V-oc as high as 0.91 V). These rigid polymers also possess respectable hole mobilities of 1.50 x 10(-3), 6.0 x 10(-4), and 3.9 x 10(-4) cm2 V-1 s(-1) for PDTC, PDTSi, and PDTP, respectively. The combined high Voc and good hole mobility enable bulk heterojunction photovoltaic cells to be fabricated with relatively high power conversion efficiency (PCE as high as 3.74% for the PDTC-based device).