Synthesis of polyindole nanoparticles and its copolymers via emulsion polymerization for the application as counter electrode for dye‑sensitized solar cells

Abstract

In this research, aniline–indole copolymer nanoparticles with different molar ratios were synthesized successfully by chemical oxidative polymerization, using ferric chloride ( FeCl3) as an oxidant agent in sodium dodecylsulfate (SDS) micellar solution. For comparison, pure polyindole and polyaniline nanoparticles were also prepared at the same conditions. The synthesized polymer powders were characterized using X-ray diffraction (XRD), UV–Vis absorption, thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FE-SEM). The XRD and FE-SEM results demonstrated that the polymers and copolymers have semi-crystalline structure with sub-nanoparticle sizes (< 100 nm) and almost the same morphology. After characterization, powders (polyindole, polyaniline, and their copolymers) were suspended in distilled water, then were deposited on the fluorine-doped tin oxide (FTO), by spin coating technique. The products were used as counter electrode (CE) for dye-sensitized solar cell (DSSC). Under simulated AM 1.5 G solar light (100 mW cm− 2), the cell with pure polyindole CE showed a low-power conversion efficiency of 0.79%. Adding much more aniline monomer to the copolymers, increased the efficiency of cells, gradually, so that the efficiency reached 5.60% for pure polyaniline CE-based DSSC. In addition, the results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel all proved that the catalytic performance of polyaniline CE is superior to the other CEs. The study provides evidence that the copolymer CEs can be good catalytic materials for fabricating flexible and inexpensive DSSCs at low temperatures.