Soluble acetylenic molecular glasses based on dithienyldiketopyrrolopyrrole for organic solar cells

• Soluble acetylenic molecular glasses based on DT-DPP for OSCs have been reported.
• The optical absorption of the dye films was little affected by thermal annealing below Tg.
• The difluorenyl(2-naphthyl)amine endgroup contributes to increasing μhole and PCE.

We present the synthesis and photovoltaic response of soluble glass-forming molecules containing a dithienyldiketopyrrolopyrrole core and difluorenylarylamine endgroups, linked through an acetylene bond. Introducing the 2,6-naphthylene moiety vs. 1,4-phenylene leads to an increased glass transition temperature (Tg) and hole mobility. Thus, Tg = 107.7 °C, μh = 7.95 × 10−5 cm2 V−1 s−1 for the 1,4- phenylene compound, while Tg = 119.4 °C, μh = 9.17 × 10−5 cm2 V−1 s−1 for the 2,6-naphthylene compound. Thermal annealing the as-cast films of both compounds below Tg resulted in little change in optical absorption. The preliminary characterization of the bulk hetero-junction solar cells showed that the 2,6-naphthylene compound generally provides a higher power conversion efficiency than the 1,4-phenylene compound, due probably to its enhanced hole transport. The photoluminescence experiments show a weak exciplex emission around 880 nm for the blends containing the new dyes and PC61BM. The present work may be useful for further efforts toward high-performance cost-effective acetylenic organic semiconductors for organic solar cells with thermally stable morphology.

Introducing the 2,6-naphthyl moiety vs. 1,4-phenyl increases Tg and hole mobility, thus contributing to enhancing the power conversion efficiency.Figure optionsDownload as PowerPoint slide