Controlling Blend Film Morphology by Varying Alkyl Side Chain in Highly Coplanar Donor鈥揂cceptor Copolymers for Photovoltaic Application

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• 作者：Yaowen Li ; Yujin Chen ; Xing Liu ; Zhong Wang ; Xiaoming Yang ; Yingfeng Tu ; Xiulin Zhu
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：August 23, 2011
• 年：2011
• 卷：44
• 期：16
• 页码：6370-6381
• 全文大小：1178K
• 年卷期：v.44,no.16(August 23, 2011)
• ISSN：1520-5835

文摘

A series of varied length alkyl substituted donor鈥揳cceptor (D鈥揂) conjugated copolymers with benzo[1,2-b:4,5-b鈥瞉dithiophene (BDT) as donor and thiophene rings attached to both sides of the benzothiadiazole (TBT) moieties as acceptors were designed and synthesized. The optical and electrochemical properties showed that the absorption spectrum, the band gaps, and the energy levels of the copolymers were not affected by the varied substituted alkyls, and all these copolymers showed low band gaps around 1.75 eV. In addition, the morphologies of the blend film between copolymers and PCBM can be fine-tuned by increasing the length of substituted alkyl of the copolymers, changing from pea-like aggregation to interpenetrating network to grain-like aggregation. Bulk heterojunction photovoltaic devices were 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 showed the stable open-circuit voltage (V_oc) in the range of 0.68 to 0.74 eV, and dramatically increasing short circuit current density (J_sc) by optimizing the blending morphologies of copolymer and PCBM films. The optimized photovoltaic performance with a V_oc of 0.70 V, J_sc of 7.19 mA/cm², a fill factor (FF) of 0.52, and a power conversion efficiency (PCE) of 2.88%, was obtained by the copolymer PBDT-TBT-C8 (PBDT-TBT-C8:PC₆₁BM, 1:3 w/w, in CB solution). This is due to its low band gap and interpenetrating network morphology of PBDT-TBT-C8:PC₆₁BM blend film. The photovoltaic device based on PBDT-TBT-C8:PC₇₁BM showed a J_sc of 8.6 mA/cm² and a PCE of 3.15%.