The effect of transition metal ions (M2+=Mn2+, Ni2+, Co2+, Cu2+) on the chemical synthesis polyaniline as counter electrodes in dye-sensitized solar cells

The effect of transition metal ions (M²⁺=Mn²⁺, Ni²⁺, Co²⁺, Cu²⁺) on the chemical synthesis of polyaniline (PANI) used as a platinum-free counter electrode (CE) in dye-sensitized solar cells (DSSCs) was investigated. PANI was synthesized by co-polymerization of aniline in the presence of different transition metal ions by using potassium dichromate in acidic medium. It was found that the ion doping of PANI showed a certain catalytic activity for the regeneration of traditional iodide/triiodide (I^-/I₃ ^-) redox couples. The power conversion efficiency (η) of PANI CEs doped with Mn²⁺, Ni²⁺, Co²⁺ (4.41%, 2.36% and 2.10%, respectively) were higher than 1.94%, the value measured for PANI CE without doping. Doping with Ca²⁺ decreased the power conversion efficiency of PANI CE (PANI-Ca²⁺ η=1.41%). The electrical properties of the PANI, PANI-Ni²⁺, PANI-Co²⁺, PANI-Mn²+ and PANI-Ca²⁺ were studied by cyclic voltammetry (CV), impedance (EIS), and Tafel polarization curve. The experimental results confirmed that PANI was affected by the doping of different transition metal ions (M²⁺=Mn²⁺, Ni²⁺, Co²⁺, Ca²⁺). These results indicate a potential application of ion doped PANI as counter electrode in cost-effective DSSCs.