Hole-Transporting Poly(dendrimer)s as Electron Donors for Low Donor Organic Solar Cells with Efficient Charge Transport

摘要： Recent work on bulk-heterojunction organic solar cells has shown that photoexcitation of the electron acceptor followed by photoinduced hole transfer can play a significant role in photocurrent generation. To establish a clear understanding of the role of the donor in the photoinduced hole transfer process, we have synthesized a series of triphenylamine-based hole-transporting poly(dendrimer)s with mechanically flexible nonconjugated backbones via ring-opening metathesis polymerization and used them in low donor content solar cells. The poly(dendrimer)s were found to retain the hole transporting properties of the parent dendrimer, with hole mobilities of ～10?3 cm2/(V s) for solution processed neat films. However, when blended with [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM), the best performing poly(dendrimer) was found to form films that had balanced and relatively high hole/electron mobilities of ～5 × 10?4 cm2/(V s). In contrast, at the same concentration the parent dendrimer:PC70BM blend was found to have a hole mobility of 4 orders of magnitude less than the electron mobility. The balanced hole and electron mobilities for the 6 wt % poly(dendrimer):PC70BM blend led to an absence of second-order bimolecular recombination losses at the maximum power point and resulted in a fill factor of 0.65 and a PCE 2.1% for the devices, which was almost three times higher than the cells composed of the parent dendrimer:PC70BM blends.