Singlet/triplet exciton dissociation and charge recombination in donor-acceptor ThQs-C60 /PDIxCN2 complexes.

The donor-acceptor interface plays a critically important role in determining the power conversion efficiency of organic solar cells via controlling charge separation (CS) and recombination (CR) processes. Here, we combine the electronic structure calculations with electron transfer rate theory to clarify the CS and CR processes in ThQs-C60 /PDIxCN2 donor-acceptor complexes. The results reveal that in ThQs-PDIxCN2 the CS comes from both the dissociations of photo-induced singlet exciton and singlet fission-induced triplet exciton with a high efficiency, whereas in ThQs-C60 only the singlet exciton dissociation can take place because the triplet exciton lies below the charge-transfer exciton. However, very high CR rates in ThQs-PDIxCN2 obliterate the benefit of fast CS, inversely leading to the ThQ-C60 complex with a better cell efficiency. The present results are consistent with experimental observation and may furnish a possible patten to improve the overall conversion efficiency. © 2018 Wiley Periodicals, Inc.