Control of the active layer nanomorphology by using co-additives towards high-performance bulk heterojunction solar cells

In this work, two high boiling-point solvents (1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO)) were utilized as co-additives in ortho-dichlorobenzene (ODCB) and chlorobenzene (CB) solutions to fine tune the donor and acceptor domains in the bulk heterojunction (BHJ) of poly(benzo[1,2-b:4,5-b′]dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) and fullerene derivatives. A power conversion efficiency of 7.1% and a fill factor up to 70% were obtained for solar cells with active area of 1 cm2 when using [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) as acceptor, suggesting that an optimized morphology was achieved.

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► A fabrication process for high molecular weight PBDTTPD OPV devices was developed.
► A co-additives approach was developed to tune the nanomorphology of BHJ films.
► A PCE of 7.1% and FF of 70% were achieved on PBDTTPD and PC60BM based OPV cells.