Low bandgap polymers with low HOMO level for bulk heterojunction organic solar cells

The recent development of conjugated polymers for bulk heteroj unction organic solar cells was reviewed. Bulk heteroj unction of donor and acceptor materials with phase separation at nanometer scale can dramatically increase the efficiency via the improvement on excitons´ diffusion, separation, and the charge transport as well. Bandgap and HOMO level of the polymers as the donor are the main factors to determine the performance of organic solar cells with PCBM acceptor. To the bulk heteroj unction solar cells based on polymer/PCBM blend, the perfect polymer should bear low bandgap and low HOMO level simultaneously, thereby collaboratively increase the short circuit current and the open circuit voltage. Various promising conjugated polymer materials with low bandgap and low HOMO level are summarized, and the synthesis methods of the polymers are also introduced.