Development of s-tetrazine-based polymers for efficient polymer solar cells by controlling appropriate molecular aggregation

Abstract Two conjugated polymers PTTTz and PHTTz have been designed and synthesized by introducing s-tetrazine as electron-withdrawing moieties. Compared with PTTTz with 2-octyldodecyl-substituted tetrathiophene derivative as electron-donating moieties, PHTTz with hexyl- and 2-octyldodecyl-substituted hexathiophene derivative possesses relatively lower molecular coplanarity, larger stacking distance but more orderly molecular stacking, more red-shifted absorption, more suitable microphase separation, more efficient exciton dissociation, higher hole mobility, which lead to higher short-circuit current density (11.54 mA cm−2), fill factor (69.0%) and power conversion efficiency (PCE = 6.69%) values in PSCs. The PTTTz-based PSC shows an open circuit voltage of 1.02 V for its lower-ling HOMO energy level though the PCE of the PSC is only 5.16%. Moreover, the ternary PSC based PHTTz/PC71BM/ITIC exhibits a higher PCE value of 7.88% than the binary PSCs for more efficient exciton dissociation and complementary absorption spectrum in ternary blend film, which is one of the highest PCE values in s-tetrazine-based polymers.