Synthesis and photovoltaic properties of polythiophene stars with porphyrin core

Two novel porphyrin-polythiophene star-shaped polymer (P-bs1 and P-bs2) containing triphenylamine terminated poly(3′-hexyl-2,2′-bithiophene) and poly(3′-hexyl-2,2′-bithiophene) as four arms in the peripheral of porphyrin core were synthesized by Stille reaction. The thermal, photophysical, electrochemical and photovoltaic properties of the porphyrin-polythiophene derivatives were investigated. The porphyrin-polythiophene derivatives showed broad absorption in the region of 350 ∼ 650 nm. In particular, the absorption intensity at 450 ∼ 650 nm was greatly enhanced for the meso-substituted polythiophene derivatives, P-bs2. The photoluminescence spectra indicated that the emission peaks of porphyrin units were suppressed by the intensive emission of thiophene units. The electrochemical properties indicated that the porphyrin-polythiophene derivatives are potential electron-donor materials for bulk heterojunction solar cells and dye-sensitized solar cells (DSSCs). Polymer bulk heterojunction solar cells based on P-bs2 : PCBM (1 : 1, w/w) showed power conversion efficiencies (PCE) up to 0.61% under the illumination of AM 1.5, 100 mW cm−2, which increased by 69% compared to that of P-bs1 (0.36%). Meanwhile, higher PCE of 2.17% and 3.91% based on P-bs1 and P-bs2 polymer-sensitized solar cells were attained. The better photovoltaic properties benefited from longer arms of polythiophene derivatives.