Deposição assistida por micro-ondas de sulfeto de cobalto em superfícies eletrocatalíticas de contra eletrodo para células solares sensibilizadas por corante

Abstract

Dye-Sensitized Solar Cells (DSSC) are recently the subject of many studies for its simplicity, low cost, and promising availability. The high catalytic activity and low resistivity are two fundamental objectives for the counter electrode used in DSSCs. The present work has the purpose of gathering the desirable qualities of a counter electrode using cobalt sulfide (CoS) deposited on the fluorine-doped tin oxide (FTO) substrate by a microwave-assisted chemical bath and with the challenge of low-temperature heat treatment, in the range of 100–130 °C. This novel method of depositing CoS improves the electrocatalytic properties of Pt-free materials and offers to reduce numerous film-making steps by direct synthesis-deposition onto the FTO. A commercial Pt counter electrode was used as a reference parameter to evaluate the results obtained. Pt is widely used in counter electrodes because it has excellent catalytic properties, but it is a very expensive and rare material in nature. Characterizations by X-ray diffraction, scanning electron microscopy, X-ray dispersive energy, and optical transmission were performed to evaluate structural and morphological aspects of CoS films. Electrical characterizations were also carried out to assess electrocatalytic activities through Tafel curves, cyclic voltammetry, and electrochemical impedance spectroscopy. The characterization results served as a basis to affirm high catalytic and electrochemical activity of the CoS counter electrodes since these characteristics are significantly sensitive to particle size, crystal structure, morphology, porosity, specific surface area, and adhesion strength of the deposited films. The counter electrodes were evaluated in symmetrical dummy cells and tested in solar cells to determine photovoltaic parameters. The final result achieved with the CoS-110 counter electrode showed the lowest charge transfer resistance (0.37 cm2) and exhibited a photoconversion efficiency (PCE) of 8.39% against 7.88% of the commercial Pt, which demonstrates the promising use of a Pt-free counter electrode for high-performance DSSCs.