Efficient carbazole-based small-molecule organic solar cells with an improved fill factor.

In this study, a new acceptor-donor-acceptor (A-D-A) small molecule, DI3TCz, with carbazole as the central unit and 1,3-indanedione as the end group, was designed and synthesized for application in organic solar cells. In contrast to the molecule DR3TCz with rhodanine as end groups, DI3TCz exhibited deep a LUMO energy level and a nearly unchanged HOMO energy level with a narrow optical band gap of 1.75 eV and red shifted absorption. Compared with DR3TCz, the DI3TCz device showed a PCE of 6.46% with a remaining high V oc value of 0.97 V, improved J sc of 10.40 mA cm -1 and a notable FF of 0.65, which is the highest PCE value reported to data for carbazole-based small molecules OPVs.