Highly transparent poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT: PSS) films prepared by a facile spin-coating process were developed as counter electrodes for the configuration of bifacial dye-sensitized solar cells (DSSCs) with capability of utilizing the light from both sides. The used PEDOT:PSS films involved a pristine PEDOT:PSS film and ten modified PEDOT:PSS ones. The additives for preparing the modified PEDOT:PSS films were involved in iodine (IOD), dimethyl sulfoxide (DMSO), ethanol, acetone, glycerol, sorbitol and poly(ethylene glycol) (PEG) with different molecular weights (200, 400, 800 and 20,000). The UV-Vis spectra confirm that all the PEDOT:PSS films on fluorine-doped tin oxide substrates have excellent transparency with transmittance ranging from 78% to 83.5% at 550 nm. The bifacial DSSC using the pristine PEDOT:PSS film exhibits the efficiencies of 4.71% and 2.38% corresponding to the illuminations from the front and the rear sides, respectively. When the additives of IOD, DMSO and PEG200 are applied to modify the pristine PEDOT:PSS film, the corresponding device shows a significantly improved efficiency of 5.19%, 5.11% and 5.29% under the front illumination and an almost unchanged efficiency under the rear illumination, respectively. The strengthened efficiency is mainly attributed to the improved catalytic activity of the modified PEDOT:PSS films induced by the coarser surface and the lower sheet resistance. Moreover, the bifacial DSSCs with the three modified PEDOT:PSS films not only have a comparable front-illuminated efficiency to the conventional Pt based DSSCs but also possess a higher rear-illuminated efficiency than the latter cells. (C) 2015 Elsevier Ltd. All rights reserved.