To develop high-efficiency organic dyes for dye-sensitized solar cells (DSCs), a comprehensive understanding on the structure property relationship of metal-free organic photosensitizers is warranted. To address this issue, two organic dyes (M14 and M24) featuring, respectively, propyl chains and hexyl chains have been engineered. Interestingly, it is found that the length of alkyl chains has different effects on the performance DSCs with different electrolyte (e.g., iodine electrolyte and cobalt electrolyte). Herein, we scrutinize the effects of the length of alkyl chains in terms of light-harvesting, interfacial kinetic parameters, as well as their joint contribution to the photovoltaic performance. Furthermore, the dependence of conduction band shift and electron lifetime on the concentration of 4-tert-butylpyridine (TBP) in electrolyte is also investigated. (C) 2013 Elsevier B.V. All rights reserved.