Self-assembled bulk heterojunctions from integral molecules with nonconjugately linked donor and acceptor units for photovoltaic applications

摘要： The bi-continuous interpenetrating network of donor/acceptor with suitable phase-separated domain size is crucial for highly efficient organic bulk heterojunction solar cells considering that it guarantees effective exciton dissociation and smooth charge transport. For traditional binary blend bulk heterojunction, the photoactive layer is a simple physical mixture of donor and acceptor, the size of phase separation is primarily determined by the aggregation characteristics of the donor and acceptor respectively, it is hard to control and stabilize. To solve this problem, a kind of donor-acceptor integral molecule with donor units and acceptor units linked by non-conjugated flexible linking units has been proposed. The energy levels and the absorption spectra of the integral molecules can be easily tailed by tuning the donor and the acceptor units. Furthermore, the integral molecules can form a microphase separated bulk heterojunction of donor phase and acceptor phase through a self-assembly process of the molecule, which is governed by the flexible linking unit, responsible for connecting the donor and acceptor units. Since the donor and acceptor units of the integral molecules are connected by the non-conjugated units, the scale of aggregation and the morphology stability could be easily controlled. In this review, we first introduce the unique characteristics of the three typical donor-acceptor integral molecules and then highlight their current developments. For each donor-acceptor molecule, we attempt to give a detailed summarization on their design and synthesis, and an in-depth understanding on the basic mechanism of molecular self-assembly and the performance comparison of SMSCs. In the end, the prospect and potential improvements of donor-acceptor integral molecule are addressed, and we believe that emerging donor-acceptor molecule provide great opportunities for efficient and stable organic solar cells.