Probing Charge Transfer in Organic Photovoltaic Cells by Directly Exciting Single Electron

Abstract

In this paper, we use the first principle quantum chemistry method to calculate the electronic structures of the charge transfer excited state in P3HT/PC₆₀BM heterojunction and amphiphilic oligothiophene-C60 dyad (AMPHI). With the separation distances smaller than 4.0 Å, when PC₆₀BM molecule is placed in the middle of poly(3-hexylthiophene) (P3HT) oligomer chain hole distributes at the bridge electronic state; if the PC₆₀BM molecule is then shifted to the side of P3HT chain, electron resides at the bridge electronic state. When the separation distances are larger than or equivalent to 4.0 Å, the bridge electronic state disappears. The bridge electronic state doesn’t occur either in AMPHI probably because of the large separation distance between donor and acceptor in this molecule. The calculated maximum binding energy of the charge transfer state in P3HT/PC₆₀BM heterojunction is about 0.4 eV, in good agreement with experiments.