Molecular Engineering of Copolymers with Donor鈭扐cceptor Structure for Bulk Heterojunction Photovoltaic Cells Toward High Photovoltaic Performance

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• 作者：Yaowen Li ; Bin Xu ; Hui Li ; Weidong Cheng ; Lili Xue ; Feipeng Chen ; Hongguang Lu ; Wenjing Tian
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：February 10, 2011
• 年：2011
• 卷：115
• 期：5
• 页码：2386-2397
• 全文大小：1285K
• 年卷期：v.115,no.5(February 10, 2011)
• ISSN：1932-7455

文摘

A series of donor鈭抋cceptor (D鈭扐) conjugated copolymers with benzo[1,2-b:4,5-b鈥瞉dithiophene (BDT) as donor and two different electron-accepting groups bithiophenevinyl-2-pyran-4-ylidenemalononitrile (TVM) and benzothiadiazole (BT) moieties as acceptors is designed and synthesized. The optical and electrochemical properties show that the band gaps of the copolymers are in the range of 1.70鈭?.84 eV, and the HOMO and LUMO energy levels can be tuned effectively by controlling the varied ratios between TVM and BT because of the change of the ICT interaction between donor and acceptor, the electron delocalization degree, and the electron cloud density distribution of the copolymers. Bulk heterojunction photovoltaic devices are fabricated by using the copolymers as donors and (6,6)-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) or (6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as acceptors. The optimized photovoltaic performances show that the open-circuit voltage (V_oc) was gradually increased from 0.7 to 0.94 V when decreasing the HOMO energy levels of copolymers, and the short-circuit current density (J_sc) is greatly improved by increasing the absorption spectrum in the visible region, increasing the hole mobility and optimizing the morphologies of blend films between copolymers and PCBM. The optimized photovoltaic performance with a V_oc of 0.78 V, J_sc of 5.47 mA/cm², fill factor (FF) of 0.40, and power conversion efficiency (PCE) of 1.67% under simulated AM 1.5 solar irradiation of 100 mW/cm² is obtained by the copolymer PM50 (PM50:PC₆₁BM, 1:3 w/w, in CB solution). This is due to its high hole mobility and interpenetrating network morphology of PM50:PC₆₁BM blend film. The photovoltaic device based on PM50:PC₇₁BM shows a J_sc of 8.32 mA/cm² and a PCE of 2.89%.