Synthesis of new alternating conjugated copolymers consisting of tetrazine/carbazole or tetrazine/fluorene derivatives along with thiophene spacers for photovoltaic applications

In order to investigate the relationships between chemical structures of conjugated polymers and their properties with respect to photovoltaic applications, two new copolymers consisting of an electron-deficient tetrazine unit and either an electron-rich carbazole (PCTz) or fluorene (PFTz) along with thiophene spacers were synthesized. The estimated electrochemical bandgap and HOMO level of PCTz and PFTz were 2.23/−5.32 eV and 2.48/−5.60 eV, respectively. PCTz had a very high absorption coefficient, which was even higher than poly(3-hexyltiophene) in chloroform solution. The bulk heterojunction photovoltaic devices fabricated using PCTz and [6,6]-phenyl-C71-butyric acid methyl ester had a high open-circuit voltage (1.0 V) under AM 1.5 G illumination at 100 mW/cm2 with a power conversion efficiency of 2.13%.