Tunable Novel Cyclopentadithiophene-Based Copolymers Containing Various Numbers of Bithiazole and Thienyl Units for Organic Photovoltaic Cell Applications

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• 作者：Kuang-Chieh Li ; Jen-Hsien Huang ; Ying-Chan Hsu ; Po-Ju Huang ; Chih-Wei Chu ; Jiann-T’ ; suen Lin ; Kuo-Chuan Ho ; Kung-Hwa Wei ; Hong-Cheu Lin
• 刊名：Macromolecules
• 出版年：2009
• 出版时间：June 9, 2009
• 年：2009
• 卷：42
• 期：11
• 页码：3681-3693
• 全文大小：442K
• 年卷期：v.42,no.11(June 9, 2009)
• ISSN：1520-5835

文摘

Six novel conjugated copolymers (P1−P6) containing coplanar cyclopentadithiophene (CPDT) units (incorporated with bithiazole/thienyl-based monomers) were synthesized and developed for the applications of polymer solar cells (PSCs). Copolymers P1−P6 covered broad absorption ranges from UV to near-infrared (400−800 nm) with narrow optical band gaps of 1.70−1.94 eV, which are compatible with the maximum solar photon reflux. Partially reversible p- and n-doping processes of P1−P6 in electrochemical experiments were observed. Compared with those previously reported CPDT-based narrow band gap polymers, the proper molecular design for HOMO/LUMO levels of P1−P6 induced relatively high photovoltaic open-circuit voltages in the PSC devices. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed highly self-assembled π−π stackings. Under 100 mW/cm² of AM 1.5 white-light illumination, bulk heterojunction PSC devices containing an active layer of electron donor copolymers P1−P6 blended with electron acceptor [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) in the weight ratio of 1:1 were explored, and the external quantum efficiency (EQE) measurements showed a maximal quantum efficiency of 60%. The PSC device containing P4 in the weight ratio of 1:2 with PCBM gave the best preliminary result with an overall power conversion efficiency (PCE) of 3.04%, an open-circuit voltage of 0.70 V, a short-circuit current of 8.00 mA/cm², and a fill factor of 53.7%.