In this study, we report improved power conversion efficiencies of various carbon based quasi-solid state electrolytes/DSSCs by optimising the thickness of TiO2 layer, incorporation of TiO2 scattering layer and application of dense compact surface layers of TiO2 on working electrodes. Single wall carbon nanotube (SWCNT) based quasi-solid state electrolytes showed increased power conversion efficiencies from 1.43% to 3.49%. For the mixture of graphene and SWCNTs the power conversion efficiencies improved from 2.50% to 2.93%. However, graphene based quasi-solid state electrolytes displayed small decreases in power conversion efficiencies from 2.10% to 1.96% due to the more viscous nature of this electrolyte. Electrochemical Impedance Spectroscopy (EIS) demonstrated that the addition of these various carbon based nanomaterials into PMII significantly decreases the charge transfer resistance at the counter electrode and hence the much better performance obtained with carbon based quasi-solid state electrolytes compared to pure PMII based DSSCs. (C) 2014 Elsevier Ltd. All rights reserved.