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

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journal contribution
posted on 17.04.2020, 15:11 by Wei Jiang, Martin Stolterfoht, Hui Jin, Paul L. Burn
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.