The role of the charge-transfer states in the ultrafast excitonic dynamics of the DTDCTB dimers embedded in a crystal environment

Photoinduced excitonic dynamics plays an essential role in the solar energy conversion of organic solar cells. Following our previous work [J. Phys. Chem. C 121 (2017) 27263] on the energy transfer of the 2-[[7-(5-N,N-ditolylaminothiophen-2-yl)-2,1,3-benzothiadiazol-4-yl]methylene]malononitrile (DTDCTB) dimer, we try to understand the role of the intermolecular charge-transfer (CT) electronic states in the excitonic dynamics. When the CT states lie higher than local excited (LE) states and the LE/CT couplings are weak, the CT state plays a minor role. When the LE/CT couplings are strong enough, the CT states start to be unneglectable. When the CT states show lower energies than LE states, the CT states become important. In addition, the near-resonance condition may appear in the excitonic dynamics, resulting in the low-frequency oscillation pattern in the time-dependent electronic populations. This work provides the interesting insight on the role of the CT states in the excitonic dynamics of organic photovoltaic systems.