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

Abstract

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 viaStille 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 × 10⁻³, 6.0 × 10⁻⁴, and 3.9 × 10⁻⁴ cm² V⁻¹s⁻¹ for PDTC, PDTSi, and PDTP, respectively. The combined high V_oc and good hole mobility enable bulk hetero-junction photovoltaic cells to be fabricated with relatively high power conversion efficiency (PCE as high as 3.74% for the PDTC-based device).