Planar alternating copolymer of benzodithiophene and bisthiophenephthalimide:Synthesis and photovoltaic properties

A new planar alternating D-A copolymer of benzodithiophene (BDT) and bisthiophene-phthalimide (PhBT), PBDTPhBT, was synthesized by Stille coupling reaction. The polymer possesses high thermal stability, good solubility in common organic solvents and strong absorption in the wavelength range of 380~580 nm. The results of molecular simulation indicate a planar main chain of the polymer. The optical bandgap of PBDTPhBT is 2.10 eV, its HOMO energy level measured by electrochemical method is -5.23 eV. Bulk-heterojunction polymer solar cells (PSCs) were fabricated, based on PBDTPhBT as donor, PC 70 BM as acceptor (D/A weight ratio of 1: 1) and Ca/Al as negative electrode. Under the illumination of AM1.5, 100 mW cm -2 , the PSC displayed an open circuit voltage of 0.79 V, a short circuit current of 5.63 mA cm -2 , and energy conversion efficiency of 1.76%.