Nanoscale phase separation control in rationally designed conjugated polymer solar cells processed using co-additives

Abstract

A conjugated polymer based on benzo[1,2-b:4,5-b′]dithiophene with a thiophene-conjugated side chain and N-alkylthieno[3,4-c]pyrrole-4,6-dione was synthesized. When shortening the alkyl to linear hexyl on thiophene, the polymer (PBDT2T6–TPD) still has good solubility in common solvents and the hole mobility is improved. By introducing two additives (1,8-diiodooctane and 1,6-dibromohexane) as co-additives in chlorobenzene solution, a nanoscale phase separation with excellent bicontinuous interpenetrating network and balanced hole mobility and electron mobility was obtained in the blend film of PBDT2T6–TPD and [6,6]-phenyl C61 butyric acid methyl ester. Combined with an appropriate side chain of polymer and post-processing of the device, the solar cells exhibit a power conversion efficiency of 6.73% with a remarkable short circuit current density of 12.91 mA cm⁻².