Synthesis, characterization, and solar cell and transistor applications of phenanthro[1,2-b:8,7-b′]dithiophene-diketopyrrolopyrrole semiconducting polymers

Synthesis, characterization, and polymer solar cell and transistor application of a series of phenanthro[1,2-b:8,7-b′]dithiophene-based donor-acceptor (D-A)-type semiconducting polymers combined with a diketopyrrolopyrrole unit are reported. The present polymers showed some unique features such as strong aggregation behavior, high thermal stability, and short π-π stacking distance (3.5-3.6 Å), which are suitable for high performance organic materials. In addition, they have a significantly extended absorption up to 1000 nm with a band gap of ca. 1.2 eV. However, such strong intermolecular interaction reduced their solubility and molecular weights, which resulted in low crystalline nature and moderate field-effect mobility of 0.01 cm² V^-1 s^-1. Furthermore, such strong aggregation behavior led to the large-scale phase separation in the blend films, which may prevent the effective photocurrent generation, limiting J_sc and power conversion efficiency of 2.0%.