Novel Small Four-armed Molecules with Triphenylamine-bridged Structure for Organic Solar Cells Featuring High Open-circuit Voltage

In view of few attention on star-shaped molecules containing triphenylamine(TPA)unit asπ-linker,a series of small four-armed molecules,consisting of octyloxy-substituted 2,1,3-benzothiadiazole(DOBT)or 4-octyl-2-thienyl functionalized DOBT as the core,TPA asπ-bridge and 4-methylphenyl or 4-methoxyphenyl groups as terminal units,was designed and synthesized.The effects ofπbridges and substitute groups on molecular photoe-lectric performance and photovoltaic performance were fully explored.With the help of the additional thiophene-linkers incorporation,3-octylthienyl substituted molecule with end-capping 4-methylphenyl(T-BTTPAM)and 3-octylthienyl substituted molecule with end-capping 4-methoxyphenyl(T-BTTPAOM)showed stronger and broader absorption,as well as higher charge mobilities compared to the molecules without thiophene-linkers(BTTPAM and BTTPAOM).Additionally,changing substitute groups from methyl to methoxy helped BTTPAOM and T-BTTPAOM achieve better absorption properties than BTTPAM and T-BTTPAM,respectively.When paired with PC61BM as the electron acceptor to fabricate solution-processed photovoltaic devices,the four materials gave high open-circuit voltage(Voc)values over 0.90 V.These results demonstrate that our materials are promising candidates as donor materials for organic solar cells(OSCs),and further device optimization is in progress in our laboratory.