Degradation of a nano-thick Cu/Pt bilayered catalytic layer with an electrolyte in dye sensitized solar cells

This study examined the stability of a Cu/Pt bilayered counter electrode (CE) with the electrolyte and the energy conversion efficiency of dye-sensitized solar cells using a 0.45 cm² dye-sensitized solar cell (DSSC) device with a glass/FTO/blocking Iayer/Ti02/N719 (dye)/electrolyte/50 nm-Pt/50 nm-Cu/FTO/glass. For comparison, a 100 nm-thick Pt only CE DSSC was also prepared using the same method. The photovoltaic properties, such as the short circuit current density (J_sc), open circuit voltage (V_oc), fill factor (FF), energy conversion efficiency (ECE), and impedance, were checked using a solar simulator and potentiostat with time after assembling the DSSC. The microstructure of the Cu/Pt bilayer was examined by optical microscopy after 0∼30 minutes and 3 weeks. The ECE of the DSSC using the Pt only CE was 4.60 %, which did not show any time dependence. On the other hand, for the Cu/Pt CE DSSC, the ECEs after 0 minutes, 30 minutes, and 3 weeks were 5.72%, 5.03%, and 1.36%, respectively. Moreover, the interface resistance increased; 6, 7, and 40 Ω at 0 minutes, 30 minutes, and 3 weeks, respectively. The corrosion area of the Cu/Pt CE determined by an optical microscopy after 0 minutes, 30 minutes, and 3 weeks was 0, 23.40, and 51.35%, respectively. These results confirmed that the ECE and catalytic activity of Cu/Pt CE decreased drastically with time. Therefore, a DSSC using a Cu/Pt CE may be superior to the Pt only CE immediately after integrating of the device, but the performance of the former degrades drastically with time.