溶液浓度对聚(3-丁基噻吩)溶液聚集态和薄膜结晶结构的影响

Concentration Effect on the Solution-state Aggregation and Thin Film Crystalline Structures of Poly(3-butylthiophene)

共轭聚合物由于其特殊的力学、电性能或光电功能被广泛应用于各种器件中.在溶液加工过程中,其在溶液中的分子链构象和溶液聚集态会由于记忆效应传递到薄膜中,从而对薄膜凝聚态结构和性能产生重要影响.基于此,本文工作通过控制聚(3-丁基噻吩)(P3BT)的溶液浓度来调控P3BT在溶液中的链聚集态,进而深入研究溶液聚集态对P3BT薄膜的结晶结构包括晶型和结晶取向的影响,以及不同结晶结构和载流子传输性能的关系.结果表明,P3BT在低浓度的溶液中链聚集程度较弱,进而在薄膜中形成丁基侧链非交叉式排列的晶型Ⅰ结构,且以edge-on结晶取向为主;而在更高浓度的溶液中形成聚集更强的聚集体,在薄膜中形成丁基侧链交叉式排列的晶型Ⅱ结构,结晶取向为flat-on与edge-on共存.这些具有不同晶型和结晶取向的P3BT薄膜对有机场效应晶体管(OFET)的器件性能有直接影响.

Conjugated polymers have been widely applied in various optoelectronic devices because of their special mechanical,electric,and optoelectronic properties.Usually,the fabrication of conjugated polymers is based on solution processing,and the conformation and solution aggregation state of conjugated polymers can be transferred to the solid state due to the memory effect.Therefore,the solution-state aggregation of conjugated polymers has an important impact on their crystalline structure and thus property in the film state.In this work,the concentration of poly(3-butylthiophene)(P3BT)solution was adjusted to control the chain aggregation in the solution,which in turn influenced the crystalline structure including form and crystal orientation of P3BT in thin films.Moreover,the correlation between different crystalline structures of P3BT and their charge transport properties based on organic field-effect transistors(OFET)was revealed.It showed P3BT aggregated weakly in low concentrations of solutions and thus produced form I crystals in edge-on orientation in the films,which had non-interdigitated packing of alkyl side chains and a larger side-chain stacking distance.In contrast,stronger aggregation of P3BT chains was observed in the solutions with high concentrations and formⅡcrystals in the mixed flat-on and edge-on orientations were produced in the films.These P3BT formⅡcrystals had interdigitated side chains and a smaller side-chain stacking distance than that of formⅠ.These P3BT films with different forms and crystal orientations were closely related to their charge transport characteristics.