一系列单硅烷-寡聚噻吩共聚高分子膜中电荷载流子及其迁移率的研究

Charge Carriers and Their Mobilities in Films of a Series of Monosilylene-oligothienylene Copolymers

研究了一系列由单硅烷和寡聚噻吩组成的共聚高分子膜在较宽掺杂电位范围内的光谱电化学变化规律.用PSnT表示这一系列共聚高分子,其中n表示高分子链上寡聚噻吩单元中噻吩环的个数,n分别为5,7,8,10和14.结果表明在一定的掺杂电位范围内这些PSnT膜可以可逆地电致变色.PSnT膜的光谱电化学和循环伏安研究均表明在电化学掺杂过程中PSnT膜中的寡聚噻吩单元可被两步氧化.第一步氧化生成极子,极子可二聚形成π-dimers,两者之间存在着平衡.而第二步氧化生成双极子.双极子不能稳定存在于PS5T和PS7T膜中,但可稳定存在于其它具有更长寡聚噻吩单元的PSnT膜中.结合PSnT膜在不同电位下的表观迁移率数据讨论了膜中各种载流子对表观迁移率的影响.表明当掺杂电位低于两步氧化过程的平均电位Emean时,膜中表观迁移率的增加主要是由于π-dimers的形成及数量增加所引起的.随着寡聚噻吩共轭长度(n)的增加,π-dimers更易形成,因此PSnT膜中载流子的表观迁移率在更低的掺杂电位下开始增加并具有更大的增幅.

A spectroelectrochemistry study was carried out for thin films of a series of copolymers with repeat units consisting of monosilylene and oligothienylene （PSnT,π=5, 7, 8, 10 and 14, n denotes the ring number of an oligothienylene unit） over a wide window of doping potentials. It was found that the films of these PSnT samples showed reversible electrochromic change in a proper range of doping potentials. Both the spectroelectrochemistry and cyclic voltammetry studies of PSnT film indicate that during electrochemical doping the oligothienylene unit of each PSnT is oxidized in the first oxidation step to polaron in equilibrium with π-dimers, and in the second step to bipolaron. Bipolarons are not stable in PS5T and PS7T films, but can exist safely in other PSnT films with longer oligothienylene unit. The formation of π-dimers was found to be favored by extension of the oligothienylene unit in PSnT. Apparent mobilities for these copolymers with longer π-conjugation lengths started to rise at lower doping potentials and the mobility enhancement also followed an increasing order of the π-conjugation length.