Design, synthesis and photovoltaic properties of a new D–π–A polymer with extended π-bridge units
作者:Xia Guo、Maojie Zhang、Lijun Huo、Feng Xu、Yue Wu、Jianhui Hou
DOI:10.1039/c2jm32931j
日期:——
New low band gap copolymers PBDTTâDTTBT and PBDTTâDTBT using BDT-T and BT as donor and acceptor, with different Ï-bridge units thieno[3,2-b]thiophene and thiophene, respectively, were synthesized. The absorption spectra, electronic energy levels, and photovoltaic properties of the polymers were characterized. PBDTTâDTTBT and PBDTTâDTBT films show broad absorption in the visible range with an absorption edge at over 751 nm, and possess relatively low-lying HOMO levels at â5.11 eV and 5.15 eV. A high hole mobility of 1.97 à 10â3 cm2 Vâ1 sâ1 was recorded for PBDTTâDTTBT, that is two orders of magnitude higher than PBDTTâDTBT (1.58 à 10â5 cm2 Vâ1 sâ1), which is ascribed to the application of thieno[3,2-b]thiophene as Ï-bridge units. The PCE of the PSC device based on PBDTTâDTTBT/PC70BM (1â:â1, w/w) reached 6.03% with a Jsc of 12.46 mA cmâ2, a Voc of 0.78 V and a FF of 0.62, while PBDTTâDTBT/PC70BM (1â:â1, w/w) only has a PCE of 2.34% with a Voc of 0.82 V, a Jsc of 5.78 mA cmâ2 and a FF of 0.495 under the illumination of AM 1.5 G, 100 mW cmâ2. These results indicate that PBDTTâDTTBT is a promising photovoltaic material. Furthermore, it can be concluded that extending the conjugation of the backbone units, as demonstrated in this work, has little influence on the molecular energy levels, but can be seen as a feasible strategy to improve the photovoltaic properties of DâÏâA conjugated polymers by enhancing intermolecular interactions.
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