A new cobalt-terpyridine redox shuttle ([Co(Cl-phenyl-terpyridine)(2)](2+/3+)) has been synthesized, characterized, computationally investigated and then tested in photovoltaic devices, in conjunction with the prototypical N719 and Z907 ruthenium dyes. Lower efficiencies compared to the reference [Co(bpy)(3)](2+/3+) redox couple were obtained, probably due to increased recombination processes. Improvements in the devices performances were obtained by using chenodeoxycholic acid as surface co-adsorbent and as an electrolyte additive. Moreover, to better rationalize the photovoltaic results, the effect of two different counterions (TFSI and PF6) has been investigated for the reference [Co(bpy)(3)](2+/3+) electrolyte, finding a reduced efficiency for the TFSI-based electrolyte. (C) 2013 Elsevier B.V. All rights reserved.