Comparison of solar cell performance of conducting polymer dyes with different functional groups

Abstract

Conductive polymer precursors, including carboxylic acid, cyano groups, amino groups, 5,2′:5′,2″-terthiophene–3′-carboxylic acid (TTCA), 3′-cyano-5,2′:5′,2″-terthiophene (CTT), and 3′,4′-diamino-2,2′:5′,2″-terthiophene (DATT) are synthesized. Electrochemically polymerized films of the precursors on a nanocrystalline TiO2 layer are examined as photo sensitizers, and the cell performance is compared. The photovoltaic cells are assembled with a polymer-coated TiO2 layer treated with TiCl4 as an anode and a Pt layer as a cathode in a propionitrile solution containing an iodide ion-based redox electrolyte. The charge-transfer processes of polymer-dyed cells are studied using impedance spectroscopy. The polymer dyes on the TiO2 surfaces are characterized by scanning electron microscope (SEM), atomic force microscope (AFM), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). XPS results show that the conducting polymer dye, bearing a carboxylic acid group, is more strongly bound to the TiO2 layer in comparison with other groups. Various experimental parameters affecting the cell efficiency are optimized, including the scan rate, number of potential cycles, and terthiophene monomer concentration. Of these polymers, the best cell efficiency is attained for poly-TTCA containing a carboxylic acid group. The optimized cell with the poly-TTCA dye shows a short-circuit current of 6.78mAcm−2, an open-circuit voltage of 0.54V, and a fill factor of 63.6. An energy conversion efficiency of 2.32% is obtained with a cell area of 0.24cm2 under an air mass 1.5 solar simulated light irradiation of 100mWcm−2.