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...