An A-D-D-A-type small-molecule electron acceptor with chlorine substitution for high-efficiency polymer solar cells

Chlorination is a very effective technique to adjust molecular energy levels, absorption spectra and intermolecular π–π stacking of small-molecule acceptors (SMAs). On this basis, a new acceptor-donor-donor-acceptor (A-D-D-A)-type SMA IDT2-IC-4Cl with chlorinated end units was developed. Compared with the unchlorinated counterpart (IDT2-IC), the IDT2-IC-4Cl exhibited an efficient absorption ability in the range of 550–900 nm region. Moreover, the blend films of PBDB-T:IDT2-IC-4Cl exhibited better charge generation properties and more balanced charge mobilities as compared to those of PBDB-T:IDT2-IC blend films. Polymer solar cells (PSCs) based on PBDB-T:IDT2-IC-4Cl exhibited a power conversion efficiency (PCE) of 12.53% with a short-circuit current (Jsc) of 22.22 mA cm−2 and a fill factor (FF) of 69.81, while the PBDB-T:IDT2-IC device yielded a PCE of 8.18% with a Jsc of 13.23 mA cm−2 and a FF of 65.71. The results show that chlorination is an effective way to obtain high-performance SMAs.