Symmetrical squaraine (SQ) dyes with varying alkyl chain lengths have been synthesized towards their utilization as sensitizer for enhancing the photon harvesting in far-red region of solar spectrum. It has been observed that energy level of the SQ-dyes can be systematically tuned only by alkyl chain substitution. It has also been shown that SQ-dyes behave like p-type donors forming a p-n heterojunction with soluble fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) as n-type organic electron acceptor. Thin film organic photovoltaic p-n heterojunction devices have been fabricated using soluble SQ-dyes with PCBM without using any thermal evaporation technique for the active layers. A perusal of the photo-action spectra clearly corroborates that at least 0.25 eV energy barrier is necessary for the facile electron transfer from donor moiety to the acceptor after the photo-excitation. (C) 2012 Elsevier B.V. All rights reserved.