Novel NIR-absorbing conjugated polymers for efficient polymer solar cells: effect of alkyl chain length on device performance
作者:Wei Yue、Yun Zhao、Shuyan Shao、Hongkun Tian、Zhiyuan Xie、Yanhou Geng、Fosong Wang
DOI:10.1039/b818885h
日期:——
Three low bandgap conjugated polymers, i.e., PDTPBT-C8, PDTPBT-C6 and PDTPBT-C5, which consist of alternating N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole and 2,1,3-benzothiadiazole units and carry 1-octylnonyl, 1-hexylheptyl and 1-pentylhexyl as side chains, respectively, were synthesized. These polymers show strong absorption in the wavelength range of 600–900 nm with enhanced absorption coefficient as the length of alkyl chain decreases. The film morphology of the polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 (PCBM) blends is also dependent on the alkyl chain length. As the length decreases, the film becomes more uniform and the domian size decreases from 400–900 nm for PDTPBT-C8 to ∼50 nm for PDTPBT-C5. Bulk heterojunction photovoltaic solar cells (PSCs) were fabricated based on the blend of the polymers and PCBM with a weight ratio of 1:3. The device performance is dramatically improved as the length of the side chain decreases, due to enhanced film absorption coefficient and improved film morphology. With the polymer PDTPBT-C5, which carries the shortest alkyl chain, power conversion efficiency (PCE) up to 2.80% has been achieved. This result indicates that optimizing the structure of the solublizing alkyl chain is also crucial for the design and synthesis of high performance PSC polymeric materials.
合成了三种窄带隙共轭聚合物,即PDTPBT-C8,PDTPBT-C6和PDTPBT-C5,它们由交替的N-烷基二噻吩并[3,2-b:2',3'-d]吡咯和2,1,3-苯并噻二唑单元组成,并分别带有1-辛基壬基,1-己基庚基和1-戊基己基侧链。这些聚合物在600-900 nm波长范围内显示出强烈的吸收,并且随着烷基链长度的减少,吸收系数增强。聚合物和1-(3-甲氧羰基)丙基-1-苯基-[6,6]-C-61(PCBM)混合物的膜形态也取决于烷基链的长度。随着链长的减少,膜变得更加均匀,域尺寸从PDTPBT-C8的400-900 nm减小到PDTPBT-C5的约50 nm。基于聚合物和PCBM的混合物(重量比为1:3)制备了体异质结光伏太阳能电池(PSCs)。由于膜吸收系数的增强和膜形态的改善,随着侧链长度的减少,器件性能显著提高。带有最短烷基链的聚合物PDTPBT-C5,其功率转换效率(PCE)达到了2.80%。这一结果表明,优化溶解性烷基链的结构对于高性能PSCs聚合物材料的设计和合成也至关重要。