Electropolymerized polyaniline/graphene nanoplatelet/multi-walled carbon nanotube composites as counter electrodes for high performance dye-sensitized solar cells

Polyaniline (PAND/graphene nanoplatelet (GNP)/multi-walled carbon nanotube (MWCNT) composite films deposited on fluorine-doped tin oxide (FTO) substrates were successfully fabricated through electrochemical method without pre-treatment of GNP and MWCNT to provide a lower cost counter electrode (CE) for dye sensitized solar cells (DSSCs). By varying the contents of GNP and MWCNT in the PANI composite CE, the shortcircuit current density of DSSC was found to linearly relate to the reduction current density of I-/I3-redox couples measured by cyclic voltammetry. The open-circuit voltage (Voc) is also highly dependent on the reduction potential of redox couples. Besides, the charge transfer resistance at the electrolyte/CE interface measured by electrochemical impedance spectroscopy has an approximately linear relationship with the sheet resistance of PANI composite CE. Notably, the DSSC with the CE fabricated by the weight ratio of PANI/GNP/MWCNT at 1:0.003:0.0045 yielded the highest power conversion efficiency of 7.67 +/- 0.05%, which is comparable with the conventional Pt cell (7.62 +/- 0.07%).