Properties of a counter electrode with cobalt silicides in a dye sensitized solar cell

Cobalt silicide was used as a counter electrode to replace the Pt catalytic layer of a dye-sensitized solar cell (DSSC) device. 100 nm Si/ 100 nm Co on quartz was formed by sputtering and cobalt-silicides were formed by vacuum heat treatment at 500°C and 700°C for 30 min, respectively. Field emission scanning electron microscopy (FE-SEM) was used to analyze the surface microstructure. X-ray diffraction (XRD) and Auger electron spectroscopy (AES) depth profiling analysis were used to confirm the phases. Also, cyclic-voltammetry (CV) analysis was employed to confirm the catalytic activity and photovoltaic properties were confirmed using a simulator and potentiostat. The microstructure analysis indicated that the 500°C and 700°C silicidation led to a uniform planar layer and island-like agglomerates, respectively. In the XRD and AES results, those phases were structures of quartz/CoSi/Co and quartz/dot-(CoSi₂/Co). CV analysis showed that Si/Co and CoSi/Co exhibited catalytic activity, while dot-(CoSi₂/Co) did not show catalytic activity due to the isolated dot structure. The energy conversion efficiencies of DSSCs with CoSi/Co and dot-(CoSi₂/Co) were 3.75% and 0%, respectively, while that of Pt employed DSSC was 5.13%. Our result implies that using the nano-thick CoSi as a reduction catalytic layer may be an effective replacement for Pt.