Comparison of thiophene- and selenophene-bridged donor–acceptor low band-gap copolymers used in bulk-heterojunction organic photovoltaics
作者:Hung-Yang Chen、Shih-Chieh Yeh、Chin-Ti Chen、Chao-Tsen Chen
DOI:10.1039/c2jm33735e
日期:——
We report a detailed comparison of absorption spectroscopy, electrochemistry, DFT calculations, field-effect charge mobility, as well as organic photovoltaic characteristics between thiophene- and selenophene-bridged donorâacceptor low-band-gap copolymers. In these copolymers, a significant reduction of the band-gap energy was observed for selenophene-bridged copolymers by UV-visible absorption spectroscopy and cyclic voltammetry. Field-effect charge mobility studies reveal that the enhanced hole mobility of the selenophene-bridged copolymers hinges on the solubilising alkyl side chain of the copolymers. Both cyclic voltammetry experiments and theoretical calculations showed that the decreased band-gap energy is mainly due to the lowering of the LUMO energy level, and the raising of the HOMO energy level is just a secondary cause. These results are reflected in a significant increase of the short circuit current density (JSC) but a slight decrease of the open circuit voltage (VOC) of their bulk-heterojunction organic photovoltaics (BHJ OPVs), of which the electron donor materials are a selenophene-bridged donorâacceptor copolymer: poly9-dodecyl-9H-carbazole-alt-5,6-bis(dodecyloxy)-4,7-di(selenophen-2-yl) benzo[c][1,2,5]-thiadiazole} (pCzSe) or poly4,8-bis(2-ethylhexyloxy)benzo[1,2-b;4,5-bâ²]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-di(selenophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pBDTSe), or a thiophene-bridged donorâacceptor copolymer: poly9-dodecyl-9H-carbazole-alt-5,6-bis(dodecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pCzS) or poly4,8-bis(2-ethylhexyloxy)benzo[1,2-b;4,5-bâ²]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pBDTS); the electron acceptor material is [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Judging from our device data, the potential SeâSe interactions of the selenophene-bridged donorâacceptor copolymers, which is presumably beneficial for the fill factor (FF) of BHJ OPVs, is rather susceptible to the device fabrication conditions.
我们报告了噻吩桥和硒吩桥桥供体-受体低带隙共聚物之间的吸收光谱、电化学、DFT 计算、场效应电荷迁移率以及有机光伏特性的详细比较。在这些共聚物中,通过紫外-可见吸收光谱和循环伏安法观察到硒吩桥联共聚物的带隙能量显着降低。场效应电荷迁移率研究表明,硒吩桥联共聚物空穴迁移率的增强取决于共聚物的增溶烷基侧链。循环伏安实验和理论计算均表明,带隙能量的降低主要是由于LUMO能级的降低,HOMO能级的升高只是次要原因。这些结果反映在其体异质结有机光伏(BHJ OPV)的短路电流密度(JSC)显着增加,但开路电压(VOC)略有下降,其中电子给体材料是硒吩-桥联供体-受体共聚物:聚9-十二烷基-9H-咔唑-alt-5,6-双(十二烷氧基)-4,7-二(硒酚-2-基)苯并[c][1,2, 5]-噻二唑} (pCzSe) 或聚4,8-双(2-乙基己氧基)苯并[1,2-b;4,5-b−2]二噻吩-alt-5,6-双(十二烷氧基)- 4,7-二(硒酚-2-基)苯并[c][1,2,5]-噻二唑} (pBDTSe),或噻吩桥供体-受体共聚物:聚9-十二烷基-9H-咔唑-alt-5,6-双(十二烷氧基)-4,7-二(噻吩-2-基)苯并[c][1,2,5]-噻二唑} (pCzS) 或聚4,8-双( 2-乙基己氧基)苯并[1,2-b;4,5-b-2]二噻吩-alt-5,6-双(十二烷氧基)-4,7-二(噻吩-2-基)苯并[c][ 1,2,5]-噻二唑} (pBDTS);电子受体材料为[6,6]-苯基-C61-丁酸甲酯(PCBM)。从我们的器件数据来看,硒吩桥联供体-受体共聚物潜在的 Se-Se 相互作用可能有利于 BHJ OPV 的填充因子 (FF),但它相当容易受到器件制造条件的影响。