方酸菁分子中烷基取代基碳链长度对光伏器件活性层形貌的影响

Influence of the length of alkyl substituents on the morphology of the active layer of photovoltaic devices using squaraine as electron donor

以2,4-双[4-(N,N-二苯氨基)-2,6-二羟基苯基](SQ-H)方酸菁为骨架,通过向氮原子上所连接的4个苯基上引入不同长度的烷基取代基(甲基、乙基、正丁基和正己基),合成了分子SQ-C1/C2/C4/C6,并研究了其分子结构与光电性能的构效关系.研究结果显示,对于基于该骨架的化合物而言,烷基链的增加会使分子的摩尔消光系数降低,同时,分子与PC_(71)BM共混膜的粗糙度及相分离程度逐渐增加.接触角测试结果表明,这一形貌变化的本质是由于随不同长度烷基链(疏水性不同)的引入,改变了原有分子骨架的表面能,从而导致其与受体材料间的表面能差异改变所致.

A series of squaraine dyes bearing similar molecular skeleton of 2-[4-（N,N-diphenylamino）-2,6-dihydroxyphenyl] squaraine, but different alkyl groups （methyl, ethyl, n-ethyl and n-hexyl） on their nitrogen atoms （SQ-C1/C2/C4/C6）, have been designed and synthesized, and the relationship between molecular structures and photovoltaic properties of these dyes was investigated. The results revealed that with increasing alkyl chain length, the molar extinction coefficient of the squaraine compound deceases, while the roughness hence the extent of phase separation of squaraine-PC71BM blend film increased gradually. Water contact measurement results indicated that these morphological changes could be attributed to the change in the surface energy of the squaraine compounds upon different alkyl substitution （i.e., different hydrophobic interaction）, which resulted in the change in the difference of surface energy between donor and acceptor materials.