Synthesis of n-type conjugated polymers for bulk heterojunction solar cells

Abstract

A new conjugated alternating donor-acceptor copolymer is synthesized from perylene diimide and the benzodithiophene derivative via the Suzuki reaction. Temperatures corresponding to the 10% weight loss of the copolymer in air and argon are 336 and 362°C. The copolymer is soluble in common organic solvents. The maxima of absorption spectra of the copolymer in chloroform solution and thin films are at 456 and 567 and at 444 and 567 nm, respectively. The optical band gap, as calculated from the onset of the absorption spectrum, is 1.74 eV, and the electrochemical band gap is 1.89 eV. The energies of HOMO and LUMO derived from the onset of the first oxidation and reduction potential of the cyclic voltamperogram are −5.97 and −4.08 eV. It is found that the solar cell with copolymer-to-poly(3-hexylthiophene) = 1: 1 features the best characteristics: The open circuit voltage is 0.54 V, the short circuit current is 0.976 mA/cm2, the fill factor is 0.397, and the efficiency is 0.14%. The conjugated polymer based on perylene diimide belongs to the class of n-type polymers and shows promise as an acceptor material for all-polymer bulk heterojunction solar cells.