Hot Charge-Transfer States Determine Exciton Dissociation in the DTDCTB/C60 Complex for Organic Solar Cells: A Theoretical Insight

• Published in: Journal of physical chemistry. C
• Main Authors: Shen, Xingxing, Han, Guangchao, Fan, Di, Xie, Yujun, Yi, Yuanping
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.05.2015
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp512574d

To understand charge-transfer (CT) processes at the donor/acceptor interface of DTDCTB/fullerene solar cells, we have investigated the electronic couplings and the rates for exciton-dissociation and charge-recombination processes based on two representative intermolecular geometries of the DTDCTB/C60 complex by means of quantum-chemical calculations. Consistent with the experimental measurements of the time scale of over subns or even ns for charge recombination (CR), the calculated CR rates are lower than 1010 s–1 and in most cases, below 109 s–1. The calculated rates for exciton dissociation into the CT ground state are mostly lower than 1010 s–1, which is, however, in sharp contrast with the ultrafast charge separation (∼100 fs) observed experimentally. Interestingly, our calculations point out that excitons are able to dissociate into a higher-energy excited CT state much faster, with the rates being as large as about 1012 and 1014 s–1 in all cases for excitons based on C60 and DTDCTB, respectively. Thus, exciton dissociation in the DTDCTB/C60 complex is determined by the hot CT states. As the excess energy of the excited CT state can facilitate the geminate electron and hole to further separate at the donor/acceptor interface, our theoretical results suggest that the high performance of the DTDCTB/fullerene-based solar cell can be mainly attributed to the fact that excitons dissociate via the hot CT states to effectively form mobile charge carriers.